Note: Descriptions are shown in the official language in which they were submitted.
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INTERFACE MEMBERS AND HOLDERS FOR MICROFLUIDIC
ARRAY DEVICES
Cross-Reference to Related Applications
This application claims the benefit of U.S. patent application Serial
No. 10/305,045, filed November 26, 2002, which is a continuation-in-part of
U.S.
patent application Serial No. 10/174,343, filed June 17, 2002 and is a
continuation-
in-part of U.S. patent application Serial No. 10/061,001, filed January 30,
2002,
which claims the benefit of U.S. patent application Serial No. 60/341,069,
filed
December 19, 2001, all of which are hereby incorporated by reference in their
entirety.
Technical Field
The present invention relates to microfluidic devices, and more
particularly, to microfluidic array devices that can be used to deliver one or
more
samples through one or more nozzles that are formed as part of the
microfluidic
array device. Exemplary interface members and holders for holding the
microfluidic device as the microfluidic device is used in a given application
are also
disclosed as well as exemplary uses for the microfluidic array devices. For
example, the microfluidic array device is suitable for operations designed for
lab-on-
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a-chip functions including analysis of components in the sample fluid by means
of
optical spectrometry, mass spectrometry, etc.
Back round
There has been a growing interest in the development and
manufacturing of microscale fluid systems for the acquisition of chemical and
biochemical information and as a result of this effort, microfluidics is
considered an
enabling technology for providing low cost, high versatility devices to
operations,
such as combinatorial chemistry for drug lead discovery and large-scale
protein
profiling to name a few. Generally, a microfluidic device (which is also often
referred to as a lab-on-a-chip device) is a planar device having one or more
micron
sized channels formed therein and can also include reservoirs, valves, flow
switches, etc. The microfluidic features axe designed to carry out complex
laboratory functions, such as DNA sequencing.
In the absence of using microfluidic devices, the above processes and
others are carried out in a manner that is very time intensive and thus,
costly. For
example, large-scale protein profiling is commonly carried out laboriously but
pervasively in the biotechnological and pharmaceutical industries. One
particular
application of microfluidic devices is to provide microfluidic channels that
represent
the means to separate analytes in a mixture using techniques, such as
capillary
electrophoresis and liquid chromatography.
Microfluidic devices have traditionally been fabricated from
substantially planar substrates with microfabrication techniques that have
been
borrowed from the electronics industry, such as photolithography, chemical
etching,
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and laser ablation techniques. When constructing the microfluidic devices in
this
manner, the microfluidic channels that are formed lie parallel to the surface
of one
planar surface of the substrate, and the channel is sealed by bonding a second
planar
substrate to the planar substrate containing the channel. The techniques for
detecting materials, such as analytes, that are disposed in the microfluidic
channels
have for the most part been mainly optical techniques. Fluid transport in the
microfluidic devices traditionally entails using electroosmotic,
electrokinetic and/or
pressure-driven motions of liquid and particles as the means for fluidly
transporting
such materials.
While the stacking of multiple layers of planar substrates to form a
microfluidic structure having layered microfluidic channels is possible in
terms of its
fabrication, the prevailing detection technology (optically based detection
technology) limits the practicality of fabricating such a structure since
parallel
operation of multiple layers of the planar substrates containing multiple
microfluidic
separation channels is not practical due to each microfluidic separation
channel
requiring its own light source and detector.
One detection technology that is fast becoming the detection
technique of choice in the biotechnology and pharmaceutical industries is mass
spectrometry (MS). Mass spectrometry provides more chemical information about
the material being tested (e.g., analytes) than other single detection
techniques. For
example, molecular weight and even chemical composition of the analytes from
small drug candidate molecules to large protein molecules can be successfully
analyzed by mass spectrometry (MS) and its related technique that is referred
to as
MS-MS. In MS-MS, a molecule is ionized and analyzed for molecular weight in
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the first stage of the mass spectrometer, and then the same molecular ion,
called the
"parent", is fragmented inside the mass spectrometer to produce "daughter"
ions
that are further analyzed to give the chemical composition of the parent
molecule.
While some progress has been made to interface microfluidic devices
with a mass spectrometer, there are still several shortcomings that must be
overcome in order to make this interfacing process more practical. For
example,
one technique that has been discussed involves drilling a small hole, large
enough to
accommodate a glass or quartz capillary, into the end of the microfluidic
channel
that is formed by glass substrates and a glass or quartz capillary is then
inserted into
the drilled hole to act as a nozzle for electrospray ionization. This approach
is
laborious and is impractical for high throughput operations where many such
holes
have to be drilled sequentially into the substrates.
In another technique that has been disclosed, a protrusion termed
"electropipette" extends from the edge of the substantially planar substrate.
The
microfluidic channel in this extended region is formed by two planar
substrates as in
the microfluidic channels that are formed in the rest of the microfluidic
device. The
outside dimensions of the tip structure include a thickness that is equal to
the
thickness of the two planar substrates. It has also been disclosed to
fabricate an
array of nozzles using microfabrication techniques, such as deep ion reactive
etching
on a silicon wafer. However, the use of silicon wafers as the substrates
greatly
limits the ability to individually activate each nozzle because of the
potential of
dielectric breakdown caused by the high voltage applied to the nozzle to
create the
electrospray conditions, and the volume behind the nozzle made by deep ion
reactive etching is extremely difficult to be accessed by conventional means
of liquid
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handling equipment. Integrating this silicon-based nozzle array to
microfluidic
devices, which are typically made of glass or polymers, is also extremely
difficult.
The cost of fabricating the nozzles on silicon is also very high.
While injection molding has been discussed as a process for forming
microfluidic devices, there are a number of limitations that have equally been
associated with such discussion of injection moldable microfluidic devices.
For
example, it has heretofore been discussed that there are limitations on what
size
dimensions can be formed when an injection molding process is used to form the
microfluidic features. Prior to the present applicant, there was a lack of
appreciation and understanding that an injection molding process can be used
to
form a microfluidic device having microfluidic features with dimensions less
than
100 ~,m. As a result, the use of injection molding as a fabrication process
was
limited since many rnicrofluidic applications require the microfluidic device
to have
microfluidic features (e. g. , channels) that have dimensions less than 100
~,m and
more particularly, less than 50 Vim.
It would therefore be desirable to provide microfluidic devices,
especially microfluidic array devices incorporating nozzles, that overcome the
deficiencies of the traditional microfluidic devices and more particularly,
the
deficiencies that are related to the techniques for fabricating these devices
and also
to the use of such devices.
Summary
The present application generally relates to microfluidic devices.
According to one aspect, a microfluidic device is provided and includes a body
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having a first surface and an opposing second surface. At least one channel is
formed through the body such that the channel extends from the first surface
to the
opposing second surface with the channel having an open reservoir section
formed
at the first surface. The micxofluidic device further includes at least one
nozzle that
is disposed along the second surface. The nozzle is in fluid communication
with one
channel such that each channel terminates in a nozzle opening that is formed
as part
of the nozzle tip. Unlike traditional microfluidic devices, the exemplary
microfluidic device has one or more channels that are open at each end and are
formed substantially perpendicular to both the first surface and the second
surface
where the nozzle is formed.
According to another aspect, the nozzle is conically shaped with the
channel extending therethrough and terminating at the nozzle opening. In one
exemplary embodiment, the nozzle opening has a diameter equal to or less than
100
~,m, preferably equal to or less than 50 p.m and more preferably, equal to or
less
than 20 Vim; and an outside diameter of the nozzle, as measured at a tip
portion
thereof, is less than about 150 ~,rn and preferably is equal to or less than
about 100
Vim, and more preferably equal to or less than 50 ~.m. In another aspect of
the
present application, the microfluidic nozzle array device is formed by an
injection
molding process that permits the microfluidic nozzle array device to have the
above
dimensions.
In yet another embodiment, a member for holding at least one
microfluidic device and providing an interface between the at least one
microfluidic
device and a second device is provided. The at least one microfluidic device
has a
plurality of reservoirs formed therein and the member includes a body having
an
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upper face and a lower face and a plurality of open well members formed
therein.
Each well member is defined by a well wall and includes a first end and an
opposing
second end, wherein the second end is configured and dimensioned for
frictionally
engaging the at least one microfluidic device such that at least some of the
open well
members and the reservoirs of the microfluidic device align with one another.
The
member thus not only represents means for retainingly holding the at least one
microfluidic device but it also represents means for increasing an effective
volume
of the reservoir of the microfluidic device since the open well members that
align
with the reservoirs receive sample that flows into the reservoirs and
ultimately, the
nozzles.
Moreover and according to another exemplary embodiment of the
present application, an apparatus for interfacing with a mass spectrometer to
perform a nanospray application is provided. The apparatus includes a
microfluidic
device having a body including a first surface and an opposing second surface.
The
body has at least one channel formed therein and extending through the body
from
the first surface to the second surface, wherein the channel has a reservoir
section
that is open at the first surface and at least one nozzle disposed along the
second
surface. The nozzle is in fluid communication with the channel such that one
end of
the channel terminates in a nozzle opening that is formed as part of a tip of
the
nozzle. The apparatus also includes a frame disposed around a periphery of the
microfluidic device such that the microfluidic device is securely held therein
and a
holder having first and second retaining members spaced apart a sufficient
distance
for the frame to be disposed between and held in place by the first and second
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retaining members, wherein in a retained position, the at least one nozzle is
positioned for spraying a sample into an inlet of the mass spectrometer.
In another embodiment, a shield is coupled to at least one of the
frame and the holder so that one face of the shield faces the second surface
of the
microfluidic device. The shield has at least one aperture formed therein which
is in
axially alignment with the tip of the at least one nozzle. The shield is
utilized as a
means for preventing or controlling the build-up of the electric field on the
polymeric nozzle array device. If the static electric fields are not drained
away
from the insulating polymer surface during the spray, the stray fields that
accumulate on the insulating surface will prevent the ions in the spray from
passing
into an inlet of an analyzer or the like. The above shield overcomes this
situation.
These and other features and advantages of the exemplary
embodiments disclosed herein will be readily apparent from the following
detailed
description taken in conjunction with the accompanying drawings, wherein like
reference characters represent like elements.
Brief Description of the Drawing Figures
The foregoing and other features of the exemplary embodiments will
be more readily apparent from the following detailed description and drawings
of
illustrative embodiments that are not necessarily drawn to show exact likeness
or
necessarily to scale in which:
Fig. 1 is a top perspective view of a microfluidic device having an
array of nozzles incorporated therein according to a first exemplary
embodiment;
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Fig. 2 is a cross-sectional view taken along the line 2-2 of Fig. 1;
Fig. 3 is a top plan view of the microfluidic device according to Fig.
1 illustrating placement of electrodes around the nozzles and the connections
between the electrodes and electrical contacts formed at one edge of the
microfluidic
device;
Fig. 4 is a top perspective view of a microfluidic device having an
array of nozzles incorporated therein according to a second exemplary
embodiment;
Fig. 5 is a cross-sectional view of the microfluidic device according
to Fig. 4;
Fig. 6 is a perspective view of an exemplary mold used to
manufacture the microfluidic device of Fig. 1;
Fig. 7 is a cross-sectional view of first and second dies in a closed
position that is used to manufacture the microfluidic device of Fig. 4;
Fig. ~ is a cross-sectional view of first and second dies of the mold
illustrating another embodiment where a gap is formed between a pin of the
first
mold and a nozzle forming feature of the second mold;
Fig. 9 is a cross-sectional view illustrating a mold arrangement for
fabricating a micron sized nozzle opening;
Fig. 10 is a top plan view of a tile arrangement formed of a number
of strips connected to one another with each strip including a nozzle array,
wherein
one of the strips is removed and placed in close proximity to a mass
spectrometer;
Fig. 11 is a cross-sectional view of one microfluidic channel/nozzle
arrangement wherein a sample reservoir is sealed by a member having a
polymeric
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cover sheet which is insertable and movable within the reservoir for
discharging the
sample through a nozzle opening;
Fig. 12 is a cross-sectional view of one microfluidic channel/nozzle
arrangement wherein a sample reservoir is sealed by a member having an elastic
sealing base which is insertable and movable within the reservoir for
discharging the
sample through a nozzle opening;
Fig. I3 is a cross-sectional view of one microfluidic channel/nozzle
arrangement where a sample reservoir is sealed by a piston device having a
bore
extending therethrough for injecting a fluid into the sample reservoir to
cause the
sample to be discharged through a nozzle opening;
Fig. 14 is a top plan view of an exemplary microfluidic nozzle array
device;
Fig. 15 is a cross-sectional view taken along the line 14-14;
Fig. 16 is a cross-sectional side elevational view illustrating the
microfluidic device of Fig. 5 being used in UV spectrophotometry;
Fig. 17 is a top plan view of a retaining base for releasably holding a
number of microfluidic nozzle subunit structures;
Fig. 18 is a cross-sectional view taken along the line 18-18 of Fig.
17;
Fig. 19 is a top plan view of a retaining base according to another
embodiment for releasably holding a number of microfluidic nozzle subunit
structures;
Fig. 20 is a cross-sectional view of an interface plate that can be used
to assemble at least one microfluidic device having an array of nozzles;
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Fig. 21 is a cross-sectional view of a microfluidic device having an
array of nozzles with open ended tubings attached to the reservoirs thereof;
Fig. 22 is a cross-sectional view of an interface plate according to
another embodiment that can be used to assemble at least one microfluidic
device
having an array of nozzles;
Fig. 23 is a top plan view of a mass spectrometer unit and an
apparatus for deploying a microfluidic device having an array of nozzles in
the mass
spectrometer unit independent of its make;
Fig. 24 is a front elevational view of the microfluidic device of Fig.
23;
Fig. 25 is a side elevational view of the microfluidic device of Fig.
23;
Fig. 26 is a top view of a holder for securely retaining the
microfluidic device of Fig. 24;
Fig. 27 is a side elevational view of the holder of Fig. 26;
Fig. 2~ is a top view of the holder of Fig. 26 with the microfluidic
device being securely held therein;
Fig. 29 is a side elevational view of a nanospray device interface in a
mass spectrometer unit;
Fig. 30 is a perspective view of a holder for securely holding a
microfluidic device and being coupled to an apparatus that has a degree of
movement to permit positioning of the microfluidic device with respect to a
mass
spectrometer unit;
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Fig. 31 is a front elevational view of a microfluidic device having an
array of nozzles and a plurality of electrodes formed thereon;
Fig. 32 is a sectional view through one nozzle and its associated
reservoir of a microfluidic device according to another embodiment and a
conductive capillary is provided;
Fig. 33 is a cross-sectional view through a microfluidic device to
illustrate a plurality of nozzle openings being fed from a single reservoir;
Fig. 34 is a front elevational view of a microfluidic device with frame
according to another exemplary embodiment;
Fig. 35 is a side elevational view of the microfluidic device and
frame of Fig. 34; and
Fig. 36 is a front elevational view of a microfluidic device with frame
according to yet another embodiment.
Detailed Description of Preferred Embodiments
Referring first to Figs. 1-2 in which an exemplary microfluidic device
10 according to one embodiment is illustrated. The microfluidic device 10 has
a
substrate body 20 that is formed of a polymeric material, as will be described
in
greater detail hereinafter, and has at least one microfluidic channel 30 that
is formed
in the substrate body 20. More specifically, the substrate body 20 has a first
surface
22 and an opposing second surface 24 with the microfluidic channel 30 being
formed between the first and second surfaces 22, 24 such that the microfluidic
channel 30 extends the complete thickness of the substrate body 20. The
microfluidic channel 30 is thus open at both a first end 32 at the first
surface 22 and
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a second end 34 at the second surface 24. The second end 34 of the
microfluidic
channel 30 is formed in a protrusion 50 that is formed on the second surface
24 of
the substrate body 20. According to one exemplary embodiment, the protrusion
50
has a tapered shape (inward taper) such that it forms a generally conical
structure
with the open second end 34 preferably being formed at an apex of the conical
structure. The tapered protrusion 50 serves as a nozzle that delivers a sample
(i.e.,
a liquid) that is loaded into the microfluidic device 10.
It will be appreciated that in contrast to traditional microfluidic
devices, the microfluidic channel 30'is formed in a perpendicular manner in
the
substrate body 20 in that the microfluidic channel 30 is preferably formed so
that it
is substantially perpendicular to the first and second surfaces 22, 24 of the
substrate
body 20. As illustrated, a predetermined number of microfluidic channels 30
and
nozzles 50 can be formed in one substrate body 20. The microfluidic channels
30
can be arranged according to any number of different patterns. For example and
as
illustrated in the exemplary embodiment of Figs. 1 and 2, which illustrate a
preferred arrangement, a plurality of microfluidic channels/nozzles are
arranged in
regular arrays having spacing that is identical to or similar to spacing of
microtiter
plates. For example, if 96 microfluidic channels/nozzles are desired, then the
96
microfluidic channels/nozzles are arranged in an 8x12 grid with spacing of
about 9
mm between each microfluidic channel/nozzle structure. For a 384 microtiter
array, the microfluidic channels/nozzles are placed in a 16x24 grid with
spacing of
about 4.5 mm. While not entirely to scale, Fig. 2 generally illustrates a
section of a
microfluidic channel/nozzle array having spacing of about 4.5 mm.
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According to the present exemplary embodiments, each nozzle 50 is
constructed so that its dimensions are measured in microns. The specific
configurations of the nozzle 50 and the microfluidic channel 30 are best shown
in
Fig. 2. As illustrated, the first end 32 of the microfluidic channel 30 is in
the form
of a reservoir 60 (i.e., an annular cavity) that tapers inwardly to an
intermediate
channel section 36. The intermediate channel section 36 also has a tapered
construction in that it tapers inwardly toward the second end 34 and the
nozzle 50
formed at the second surface 24 of the substrate body 20. Thus, the dimensions
of
the microfluidic channel 30 are greatest at the first end 32, where the
reservoir is
formed, and are at a minimum at the second end 34 at a tip portion 52 of the
nozzle
50. According to one exemplary embodiment, the open second end 34 of the
microfluidic channel 30 formed in nozzle 50 has an inside diameter of about
100 ~m
or less, preferably equal to or less than 50 ~m and more preferably, equal to
or less
than 20 ~,m; and an outside diameter of the nozzle, as measured at a tip
portion
thereof, is less than about 150 gm and preferably is equal to or less than
about 100
~,m, and more preferably equal to or less than 50 ~.m. The inside diameter of
the
microfluidic channel 30 opens gradually in a direction away from the nozzle 50
to
about several hundred ~m as the microfluidic channel 30 traverses through the
thickness of the substrate body 20 and eventually the microfluidic channel 30
is
formed to a diameter of about 1 rnrn to define the reservoir at the first end
32. The
length of the microfluidic channel 30 can be tailored to a given application
depending upon a number of factors, such as the desired volume of the
reservoir
defined at first end 32 and also the thickness of the substrate body 20.
According to
one exemplary embodiment, the microfluidic channel 30 has a length of about 3
mm
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or greater. However, the aforementioned dimensions are merely recited to
illustrate
one exemplary embodiment and it will be understood that the microfluidic
device 10
can be fabricated to have other dimensions.
The volume of the reservoir 60 should be such that it can hold an
amount of sample material that is typically used in the applications that the
microfluidic devices are designed for. For example, the sample volume that is
used
is from sub-microliter up to 10 microliters for mass spectrometer analysis
using
electrospray. As will be described in greater detail hereinafter, the sample
material
is held in the reservoir 60 and is then transported within the microfluidic
channel 30
to the nozzle 50 where the sample materials are finally discharged through the
open
second end 34. The outside diameter of the protruding nozzle 50 also
accordingly
increases in a direction away from the tip portion 52 thereof. By forming the
reservoir 60 or input port at the first surface 22 opposite to the second
surface 24,
where the nozzle 50 is formed, a sample can easily be fed into the
microfluidic
channel 30 by injecting or otherwise disposing the sample into one or more
reservoirs 50 and then transporting the sample through the associated
microfluidic
channel 30 using techniques described in greater detail hereinafter.
Turning now to Fig. 3, the microfluidic device 10 can be fabricated
so that it finds particular utility as a means for electrospray ionization of
analytes for
mass spectrometer analysis. Electrospray is achieved by subjecting the nozzle
50 to
a voltage so that liquid and analytes (the "sample") emerge to a high electric
field.
For this particular application, the microfluidic device 10 includes a
conductive
region 70 formed on at least a portion of the nozzle 50 and optionally, the
conductive region can extend onto the second surface 24. For example, the area
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around each nozzle 50 up to the extreme end of the nozzle 50 is metallized by
evaporation techniques, printing techniques, or other suitable techniques
known in
the art to form the conductive region 70. Because the nozzle 50 in the
illustrated
embodiment has a conical shape, the conductive region 70 takes the form of a
ring-
shaped metal layer with the nozzle 50 being in the center thereof. The
thickness of
the conductive region 70 can vary depending upon the precise application;
however,
the conductive region 70 should have a sufficient thickness so that when an
electric
voltage is applied to the conductive region 70, the sample material (i.e., a
liquid)
within the microfluidic channel vaporizes and therefore can be used in
electrospray
or nanospray applications, such as electrospray ionization of analytes for a
mass
spectrometer. The microfluidic device 10, in this example, provides a low
cost,
disposable electrospray interface capable of nanospray. This device can be
fabricated to accommodate more than one sample input in order to multiplex
several
separation instruments to a single mass spectrometer.
Each of the conductive regions 70 formed around the nozzles 50 is
connected to one or more electrical contacts 80 formed at one edge of the
substrate
body 20. More specifically, the electrical contacts 80 are preferably in the
form of
conductive pads (i.e., metallized tabs) that are formed on the second surface
24 of
the substrate body 20. Fig. 3 shows one exemplary method of electrically
connecting the conductive regions 70 with the electrical contacts 80. In this
exemplary arrangement, one conductive region 70 is electrically connected via
an
electrical pathway 90 to one electrical contact 80. The electrical pathway 90
simply
provides an electrical pathway between the conductive region 70 and the
electrical
contact 80 and is therefore formed of a conductive material (e.g., a metal).
For
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example, the electrical pathway 90 can be in the form of a thin conductive
film. By
reducing the outside diameter of the tip portion 52 of the nozzle 50 (e. g. ,
to about
50 ~.m to 80 Vim), the voltage required to generate the spray is lowered.
According
to one exemplary embodiment, the voltage used to form the spray is about 5-6
KV
for a tip portion 52 having an outside diameter from about 50 ~m to 80 ~.m. It
will
be appreciated that larger sized outside diameters can be used; however, this
will
require a greater voltage to be applied to the nozzle 50 in order to form a
spray.
It will be appreciated that more than one conductive region 70 can be
electrically attached to one electrical contact 80 using separate electrical
pathways
90 or using a network of electrical pathways or a complete metal film.
However, in
this embodiment, when an electric voltage is applied to the one electrical
contact 80,
the electric voltage is applied to each of the conductive regions 70 that is
electrically
connected to the one electrical contact 80. Thus, the electric voltage can not
be
selectively delivered to individual nozzles 50 in this particular embodiment.
Now referring to Figs. 4-5, an exemplary microfluidic device 100
according to a second embodiment is illustrated. The microfluidic device 100
is
similar in some respects to the microfluidic device 10 of Figs. 1-3. The
microfluidic device 100 includes a substrate body 110 that is formed of a
polymeric
material and includes a first face 120 and a second opposing face 130. Unlike
the
embodiment illustrated in Figs. 1-3, the first and second faces 120, 130 are
not
substantially planar surfaces but rather are non-planar in nature due to each
of the
faces 120, 130 having a number of recesses and protrusions formed therein.
The microfluidic device 100 has at least one microfluidic channel 140
formed therein between the first face 120 and the second face 130 such that
the
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microfluidic channel 140 extends completely through a thickness of the
substrate
body 110 from the first face 120 to the second face 130. The microfluidic
channel
140 is thus open at both a first end 142 at the first face 120 and at a second
end 144
at the second face 130. The first face 120 includes a first perimeter wall 122
that
extends around a perimeter of the microfluidic device 100 at the first face
120
thereof. In the exemplary embodiment, the microfluidic device 100 is generally
square shaped; however, this is merely one exemplary shape for the
microfluidic
device 100 as the microfluidic device 100 can assume any number of different
shapes. Within the boundary of the first perimeter wall 122, one or more
reservoir
walls 124 are formed with the number of reservoir walls 124 equal to the
number of
microfluidic channels 140 formed in the substrate body 110. Each reservoir
wall
124 partially defines a reservoir 160 that is designed to hold a sample
material and
the reservoir wall 124 therefore also defines the first end 142 of the
microfluidic
channel 140. Both the first perimeter wall 122 and the one or more reservoir
walls
124 extend above a generally planar surface 126 (i.e., a floor) of the first
face 120
in this embodiment. A substantial portion of reservoir 160, which is defined
at the
first end 142 of the microf~uidic device 140, is therefore formed above the
planar
surface 126.
The second end 144 of the microfluidic channel ,140 is formed in a
protrusion 170 that extends outwardly from the second face 130. As with the
prior
embodiment, the protrusion 170 preferably has a tapered shape (inward taper)
such
that it forms a generally conical structure with the open second end 144 being
formed at an apex of the conical structure. The tapered protrusion 170
therefore
acts as a nozzle that can discharge a sample that is loaded into the
microfluidic
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channel 140 (e.g., in the reservoir 160). The nozzle I70 is therefore part of
the
microfluidic channel structure since the microfluidic channel 140 is formed
therethrough and terminates at the nozzle opening.
The second face 130 is also not substantially planar but rather
includes a second perimeter wall 132 that extends at least partially around a
perimeter of the second face 130. The second face 130 does contain a floor 134
that
is substantially planar. Between the second perimeter wall 132, one or more
nozzle
base sections 180 are formed with the number of nozzle base sections 180 being
equal to the number of microfluidic channels 140. The nozzle base sections 180
are
integrally formed with and extend outwardly from the floor 134 and in the
illustrated embodiment, each nozzle base section 180 has a generally annular
shape.
However, the shape of the nozzle base section 180 is not limited to an annular
shape
and instead can have any number of shapes, including a conical shape or a
tapered
shape or any other regular or irregular shape. According to one embodiment, a
IS plane that contains the upper edge of the second perimeter wall 132
generally cuts
through the interface between the nozzle base section 180 and the nozzle 170.
The
nozzle 170 therefore extends beyond the upper edge of the second perimeter
wall
I32. According to one embodiment, the diameter of the reservoir 160 is about
equal to the outside diameter of the nozzle base section 180; and therefore,
an
outside diameter of the reservoir wall 124 is greater than the outside
diameter of the
nozzle base section 180.
The specific configurations of the nozzle 170 and the microfluidic
channel 140 are best shown in Fig. 5. As illustrated, the first end 142 of the
microfluidic channel 140 is in the form of the reservoir 160. A distal end of
the
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reservoir 160 has an inwardly tapered construction that leads to an
intermediate
channel section 146. A substantial length of the intermediate channel section
146 is
formed in the nozzle base section 180. The intermediate channel section 146
also
has a tapered construction in that it tapers inwardly toward the nozzle 170
defined at
the second end 144 of the microfluidic channel 140. Thus, the dimensions of
the
microfluidic channel 140 are greatest at the first end 142 and axe at a
minimum at a
tip portion 172 of the nozzle 170. In one embodiment, the microfluidic feature
formed in the device I00 beginning with the reservoir 160 and terminating with
the
nozzle 170 is generally cylindrical in shape along its length. According to
one
exemplary embodiment, the open second end 144 of the microfluidic channel 140
formed at the tip portion 172 has an inside diameter equal to or less than 100
~,m,
preferably equal to or less than 50 hum and more preferably, equal to or less
than 20
pm; and an outside diameter of the nozzle, as measured at a tip portion
thereof, is
less than about 150 ~,m and preferably is equal to or less than about 100 p,m,
and
I5 more preferably equal to or less than 50 ~,m. The inside diameter of the
microfluidic channel 140 varies along its length due to its tapered
construction. For
example, the inside diameter of the microfluidic channel 140 opens gradually
in a
direction away from the nozzle 170 to about several hundred gm as the
microfluidic
channel 140 traverses through the thickness of the substrate body 1I0 and
eventually, the microfluidic channel 140 is formed to a diameter of about 1.5
mm to
define the reservoir 160. The length of the microfluidic channel 140 can be
tailored
in view of the construction details of the microfluidic device 100 and the
potential
applications of the device 100. In one example, the length of the microfluidic
CA 02470847 2004-06-17
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channel 140 is about 3 mm; however, this will vary depending upon the
thickness of
the device 100, the amount of sample that is to be loaded into the device,
etc.
As with the first embodiment, the microfluidic channel 140 is formed
in a substantially perpendicular manner in the substrate body 110 since the
microfluidic channel 140 is formed substantially perpendicular to both the
first and
second faces 120, 130. While, the nozzle 170 extends beyond a plane containing
the distal edge of the second perimeter wall 132, the distal end of the
reservoir wall
124 preferably lies within the same plane that contains the distal edge of the
first
perimeter wall 122. This orientation permits a cover (e.g., thin polymeric
cover
sheet) or seal member to be disposed across the distal edge of the first
perimeter
wall 122 and the distal ends of the reservoir wall 124 to effectively seal the
sample
material within the reservoir 160, as will be described hereinafter.
One will appreciate that one of the advantages of the device 100 is
that it is formed as a one piece construction in contrast to conventional
devices
which have multiple layers bonded together. In these conventional devices, the
microfluidic channel is closed by the bonding of one layer over another layer.
In
other words, two separate layers are needed to define the complete channel.
Because the present device 100 is injection-molded, separate bonded layers are
not
required.
It will be understood that the present configurations that are
illustrated herein with reference to Figs. 1-5 are merely exemplary in nature
and are
intended to merely convey exemplary embodiments. Various modifications can be
performed to the microfluidic devices depending upon a number of different
considerations, including manufacturing considerations. For example, the
nozzle
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structures do not necessarily have to have conical shapes; however, for ease
of
manufacturing, a conical shape or the like is generally preferred
According to another aspect of the present application, various
manufacturing methods are disclosed herein for manufacturing the microfluidic
array devices illustrated in Figs. 1-5. In general terms, exemplary
manufacturing
processes disclosed herein permit microfluidic nozzle array devices to be
manufactured having microscale nozzle dimensions (e.g., a nozzle tip opening
having a diameter equal to or less than 100 Vim, preferably equal to or less
than 50
~m and more preferably, equal to or less than 20 Vim; and an outside diameter
of the
nozzle, as measured at a tip portion thereof, is less than about 150 ~m and
preferably is equal to or less than about 100 Vim, and more preferably equal
to or
less than SO ~,m) and also the present microfluidic array devices
are~particularly
suited to inexpensive fabrication methods. More specifically, the microfluidic
array
devices of the present application can be manufactured by injection molding a
suitable thermoplastic using conventional injection molding techniques.
Suitable
thermoplastics include polycyclic olefin polyethylene copolymers, poly methyl
methacrylate (PMMA), polycarbonate, polyalkanes, polyacrylate polybutanol co-
polymers, polystyrenes, and polyionomers, such as Surlyn~ and Bynel~.
Polycyclic
olefin polyethylene co-polymers are particularly suitable for use in an
injection
molding process. Various grades of such polymers are commercially available
from
Ticona under the trade name Topas~ (which is a polyethylene-polycyclic olefin
co-
polymer). Furthermore, polybutyl terephthalate (PBT) can be used, as well as
polyamides, such as nylons of different grades (nylon 6-6, nylon, 6 nylon 6-
12,
etc.); polyoxymethylene (POM) and other acetyl resins; and other resins with
melt
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viscosity comparable to PBT and other properties similar to the other suitable
polymers disclosed herein. Generally, polymers that are suitable for use in
the
present injection molding process include those thermoplastic polymers with a
relatively low melt viscosity and these polymers preferably also have a high
chemical purity (preferably the polymers are without more than a few percent
of
particulate additives and are chemically inert). Other suitable polymers
include
thermoplastics blended with a lubricant (e.g., liquid crystalline polymers)
added to
help the flow and therefore this additive acts as a processing aid and other
liquid
crystalline polymers containing polymers such as Zenite~ (DuPont Company) and
the like can be used and polymers (both commercially available and non-
commercially available) that have high chemical purity, high chemical
resistivity
and thermal stability are also suitable. In some applications, injection-
moldable
elastomers may also be suitable.
In order to manufacture the present microfluidic array devices using
injection molding techniques, a mold or mold insert must first be fabricated.
The
following description of the mold is merely exemplary for one type of mold
construction which is oversimplified in terms of its construction in order to
illustrate
certain details of overall molding process. However, one of skill in the art
will
appreciate that the mold structure is readily changeable and is dictated by
the desired
construction of the microfluidic device and more particularly, the desired
construction of the microfluidic channels based on the shape, dimensions and
other
properties thereof.
The mold typically is formed of several parts that mate with one
another to form an assembled mold. The mold or mold insert is typically formed
as
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a negative impression of whatever channel architecture or device features are
desired in the microfluidic array device. A polymeric material is injected
into the
mold and then the polymeric material is cured to form the microfluidic array
device
which is then removed from the mold. Typically, the mold is formed of two mold
dies that mate together in a sealed manner and therefore after the
microfluidic
device has been formed and is sufficiently cooled, the two mold dies are
separated
to permit access and removal of the microfluidic array device.
The mold (i.e., mold dies) or mold insert can be prepared from any
number of materials that are suitable for such use, such as metal, silicon,
quartz,
sapphire and suitable polymeric materials; and forming the negative impression
of
the channel architecture can be achieved by techniques, such as
photolithographic
etching, stereolithographic etching, chemical etching, reactive ion etching,
laser
machining, rapid prototyping, ink jet printing and electroformation. With
electroformation, the mold or mold insert is formed as a negative impression
of the
channel architecture by electroforming metal and the metal mold is polished
(preferably to a mirror finish).
For non-metallic molds for injection molding, the mold can be made
of a flat, hard material such as Si wafers, glass wafers, quartz or sapphire.
The
microfluidic design features can be formed in the mold through
photolithography,
chemical etching, reactive ion etching or laser machining (which is commonly
used
in microfabrication facilities). In addition, some ceramics can be used to
fabricate
the mold or mold insert.
Molds can also be fabricated from a "rapid prototyping" technique
involving conventional ink jet printing of the design or direct lithography of
resists,
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such as Su-~ or direct fabrication of the mold with photopolymers using
stereolithography, direct 3-dimensional fabrication using polymers, and other
similar or related techniques that use a variety of materials with polymers. A
resulting polymer-based mold can be electroformed to obtain a metallic
negative
replica of the polymer-based mold. Metallic molds are particularly appropriate
for
injection molding of polymers that require the mold itself to be heated. One
commonly used metal for electroforming is nickel, although other metals can
also be
used. The metallic electroformed mold is preferably polished to a high degree
of
finish or "mirror" finish before use as the mold for injection mold. This
finish is
comparable to the finish obtained with mechanical polishing of submicron to
micron
size abrasives (e.g., diamond particles). Electropolishing and other forms of
polishing can also be used to obtain the same degree of finish. Additionally,
the
metallic mold surface should preferably be as planar and as parallel as the
Si, glass,
quartz, or sapphire wafers. In one exemplary embodiment, the metallic mold is
polished to a highly polished finish by using 1 micron diamond particles to
provide a
finish that is close to a mirror-like finish.
The present applicant has discovered that injection molding
techniques using a mold fabricated of hardened steel or other metals can be
used to
manufacture polymeric microfluidic devices having an array of micron sized
nozzle
structures with a nozzle opening having a diameter equal to or less than 100
~.m,
preferably equal to or less than 50 ~,m and more preferably, equal to or less
than 20
Vim; and an outside diameter of the nozzle, as measured at a tip portion
thereof, is
less than about 150 ~,m and preferably is equal to or less than about 100 ~.m,
and
more preferably equal to or less than 50 ~,m. Fig. 6 is a perspective view of
a mold
CA 02470847 2004-06-17
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construction 200 that is constructed to injection mold a microfluidic nozzle
array
device, as shown in Fig. 1, having the aforementioned dimensions and
properties.
Once again, the mold 200 is formed as a negative impression of the
microfluidic
device that is to be formed. The mold 200 includes a first mold die or part
210 and
a second mold die or part 230 that are constructed so that they are
complementary to
one another and mate with one another to form an injection mold assembly that
is
used to form a microfluidic nozzle array device, similar to device 10
illustrated in
Fig. 1. The mold 200 is preferably formed by electric discharge machining
(EDM).
The first mold die 210 has a first face 212 that includes a
substantially planar surface. The first face 212 has a recessed section 214
formed
therein. The recessed section 214 generally defines the outer peripheral shape
of the
microfluidic device and also the depth of the recessed section 214 defines the
thickness of the microfluidic device (except in areas where the nozzles are
formed).
Because the microfluidic device typically has a square or rectangular shape,
the
shape of the recessed section 214 will be the same or similar. For example,
the
illustrated recessed section 214 is generally square shaped. The first mold
die 210
also includes a plurality of upstanding contoured pins 216 that are spaced
across a
floor of the recessed section 214. The shape of each pin 216 directly
corresponds to
the shape of the microfluidic channel that will be formed when the mold 200 is
closed and the polymeric material is injected. More specifically, a base
section 217
of the pin 216 corresponds to the reservoir of the microfluidic channel; an
intermediate section 218 corresponds to the intermediate section of the
microfluidic
channel and a conical tip section 219 of the pin 216 corresponds to the second
end
of the microfluidic channel that is formed in the tip portion of the nozzle.
As a
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result, the dimensions of the pin 216 are greatest at the base section 217 and
the pin
216 tapers inwardly to the conical tip section 219 thereof. The spacing of the
pins
216 directly correlates to the spacing of the microfluidic channel/nozzle
structure
and therefore, the pins 216 are preferably spaced in arrays.
Now referring to Figs. 6-7, the second mold die 230 has a first face
232 that mates with the first face 212 of the first mold die 210. The first
face 232 is
substantially planar with the exception that a plurality of apertures 234 are
formed in
the second mold die 230. The apertures 234 are arranged according to a
predetermined pattern that corresponds to the arrangement of the pins 216. The
apertures 234 are sized so that they receive at least a portion of the conical
tip
sections 219 (about 500 ~m in length in one embodiment) of the pins 216 when
the
first and second mold dies 210, 230 mate with one another. The apertures 234
are
themselves contoured so that the apertures 234 taper inwardly with a lower
portion
235 of each aperture 234 having a conical shape so as to form the conical
nozzle of
the microfluidic device. When the first and second molds 210, 230 mate
together
and the pins 216 are received in the apertures 234 according to one
embodiment, the
tip sections 219 of the pins 216 extend completely to the bottom of the
apertures 234
and contact the body of the second die mold 210 that defines the closed ends
of the
apertures 234. The mold 200 of Fig. 6 is constructed to generally produce the
microfluidic device 10 of Fig. 1.
Fig. 7 shows a cross-sectional view of a mold that is constructed to
produce the microfluidic device 100 of Fig. 4. For purposes of ease of
illustration
and simplification, the reference numbers of Fig 6 will be carried over to the
description of Figs. 7-9 since each of these illustrated molds includes first
and
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second mold dies. It will be understood that the features that are formed as
part of
the first and second mold dies 210, 230 dictate the dimensions and shape of
the
features of the resulting microfluidic device.
It will therefore be appreciated that after the first and second mold
dies 210, 230 are closed and any preparation steps that are necessary for the
injection molding process are taken, the first faces of the first mold die 210
and the
second mold die 220 seat against one another to effectively seal the recessed
section
214 and the polymeric material (typically a resin) is then injected into the
closed
space that is defined in part by the recessed section 234. Fig. 7 shows a
cross-
sectional view of the first and second mold dies 210, 230 in a closed position
with
the tip section 219 of one pin 216 received within the aperture 234 and more
specifically into the sonically shaped lower portion 235 of the aperture 234.
Because the first and second mold dies 210, 230 are negative impressions of
the
resultant microfluidic device, the microfluidic channel will take the form of
the pin
216 and the nozzle of the microfluidic device is formed by the sonically
shaped
lower portion 235. More precisely, the nozzle is formed by resin filling
completely
the space between the tip section 219 of pin 216 and the tip section of the
comically
shaped lower portion 235. As previously mentioned, in this embodiment, the tip
section 219 of the pin 216 and the tip of the second mold die 230 that is
formed in
the sonically lower shaped portion 235 are in contact with one another.
Mold 200 is intended to be used a number of times over a period of
time to produce a great number of microfluidic devices and therefore the
material
that is selected for the fabrication of the mold 200 should be done so
accordingly.
In other words, a material should be selected that permits microscale features
to be
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formed in the microfluidic device and also permits a great number of
microfluidic
devices to be formed using the mold 200. One material that is suitable for use
in
fabricating the mold 200 is hardened steel. With conventional machining
technologies, such as metal turning and electric discharge machining (EDM),
the
dimensions of the tip section 219 of the pin 216, which forms the nozzle
opening,
can be limited. For example, the dimensions (i, e. , the diameter and length)
of the
tip section 219 can be limited due to manufacturing considerations. The
available
manufacturing techniques permit the outside diameter of the nozzle to be
formed to
about 50 ~,m since it is possible to inject mold a resin into the space
between the tip
section 219 and the comically lower shaped portion 235. In some areas, this
space is
only on the order of about 15 gm due to the desired dimensions of the nozzle
and
the microfluidic channel.
While, the first mold die 210 is illustrated as having a square shape,
it will be appreciated that the first mold die 210 can be formed to have any
number
of different shapes so long as the shapes of the first mold die 210 and the
second
mold die 230 permit these two components to mate with one another.
However, there are techniques available to injection mold a nozzle
opening having smaller dimensions than the aforementioned dimensions. Fig. 8
illustrates one possible injection molding arrangement to accomplish this task
and
produce nozzles having nozzle openings that are even smaller than the tip
section
219 of the pin 216. In Fig. 8, there is a gap 240 between the tip section 219
and the
comically shaped lower portion 235 after the first and second mold dies 210,
230
have been assembled. When the polymeric material (e.g., a resin) is injected
(in a
molten state) into the comically shaped lower portion 235, the pressure of the
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CA 02470847 2004-06-17
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injected resin is adjusted such that the resin does not fill the entire space
in the gap
240 and an opening (space) remains at the tip of the resulting molded nozzle
since
sufficient pressure is not present to displace the resin to the lowermost
section of
portion 235. Using this technique, the diameter of the tip section 219 of the
pin 216
can be greater than 20 ~,m since the opening of the nozzle and the outside
diameter
of the nozzle are no longer defined by the dimensions of the corresponding
parts of
mold but rather are defined by a combination of mold dimensions, gap dimension
and injection pressure. In this manner, the pins 216 do not have to be
manufactured
to have a tip section 219 on the order of 20 ~,m in order to form a nozzle
opening of
the same dimension. Instead, the tip section 219 can have a diameter greater
than
the diameter of the nozzle opening that is ultimately formed in the nozzle as
a result
of the injection molding process.
Fig. 9 illustrates one exemplary method of overshooting the injected
resin into the gap 240 formed between the tip section 219 and the tip of the
sonically
shaped lower portion 235. The nozzle opening 215 is defined by pressure used
to
inject the molten resin and the dimensions of the gap 240. By controlling
these
parameters, the dimensions of the nozzle opening can be controlled.
Injection molding as a manufacturing technology for polymer parts is
low-cost at high-volume production. However, there is considerable cost
involved
in the production of the mold itself, especially for a microfluidic nozzle
design
which has micron sized features and therefore is a demanding design in terms
of
producing a mold. If the microfluidic nozzle array device is arranged to have
the
same pattern as the microtiter plate so that commercial robotic liquid
dispensing
equipment can be used to fill the reservoirs of the microfluidic channels with
CA 02470847 2004-06-17
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samples, then tiling or combining a number of smaller microfluidic nozzle
array
devices (i.e., subunits) to form a larger structure can be used since the
microtiter
plates consist of regularly spaced sample input points in a grid pattern. For
example, the microfluidic nozzle array devices can be formed and then combined
with one another to produce a structure that has the desired number of sample
reservoirs (also referred to as sample wells or sample inputs) to receive a
desired
number of samples. For example, some common microfluidic devices contain 96
sample reservoirs (8x12 grid); 384 sample reservoirs (16x24 grid); and 1536
sample
reservoirs (32x48 grid). The tiling can be done by number of known
conventional
means, including by permanently bonding adjacent tiles together by melt
bonding,
welding, gluing, etc. In other words, any suitable method or technique for
joining
polymer structures together can be used. The subunit structures can be formed
as
individual subunit tiles (see Figs. 17-18) or the subunit structure can be in
the form
of an elongated strip that includes a number of rows of nozzles. For example,
the
strip can be formed to include 2 rows of spaced apart nozzles.
Alternatively, the user can be supplied with a base plate that has a
number of features formed therein to permit nozzle subunit structures to be
inserted
into and retained by the base plate. For example, the base plate can contain
pre-
defined receptacles that receive the nozzle subunit structures in such a way
that the
nozzle subunit structures are securely held within the base plate and are
arranged
according to a desired pattern. One or both of the base plate and the nozzle
subunit
structures can contain interlocking features to provide an interlocking
connection
between the base plate and the nozzle subunit structures. In this embodiment,
the
base plate functions as a base on which the final microfluidic nozzle array
device
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can be constructed by arranging a number of nozzle subunit structures together
and
then securely holding these subunit structures within the base plate. One
exemplary
structure for releasably holding the nozzle subunits in an interlocked manner
is
illustrated in Fig. 17 and is discussed in greater detail hereinafter in the
discussion
of Example 3.
There are a number of advantages that are obtained by tiling or
otherwise combining a number of nozzle subunit structures into a microfluidic
nozzle array device of greater dimension. First, the cost of manufacturing the
mold
for the smaller nozzle subunit structure is substantially less than the cost
of
manufacturing a mold for the entire grid of the microfluidic nozzle. Also, the
cost
of mold replacement is also substantially reduced in the case that only one
pin in the
mold is damaged. Second, the utility of the nozzle array is made more
flexible. If
an experiment does not require all of the reservoirs (e.g., 96) of the
microfluidic
device to be filled, only the needed number of nozzles or a number close
thereto can
be inserted into the base plate. At the same time, this construction still
permits
robotic dispensing of samples. For example and according to one exemplary
embodiment, one nozzle subunit structure contains 4 reservoirs and therefore,
if the
experiment only requires 60 reservoirs, then only 15 nozzle subunit structures
are
inserted into the base plate. In this manner, the potential waste or
inefficiency
related to each microfluidic device is eliminated or greatly reduced because
the
number of unused reservoirs is greatly reduced or entirely eliminated.
Third, when the microfluidic nozzle array device is used for
electrospray or nanospray in front of a mass spectrometer inlet, a common
configuration is to have the nozzle spray "off axis", i.e., the nozzle sprays
in a
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direction perpendicular to the inlet. Since the nozzle has to be placed in
close
proximity to the inlet (e.g., typically within an inch), there is often times
not enough
room in front of the inlet to accommodate the entire microtiter plate. Fig. 10
illustrates how a tiled microfluidic nozzle array microtiter plate can be used
for
electrospray in the off axis configuration. A tiled microfluidic nozzle array
300
arranged in a 96 well microtiter plate format is broken up into strips 302
with two
rows of 12 nozzles 310 each. One of the strips 302 is broken away or is
otherwise
removed from the others and is transferred (as indicated by arrow 320) to a
nozzle
mount (not shown) in front of a mass spectrometer inlet 330 of a mass
spectrometer
340. The nozzle mount holds the strip 302 and has at least an x-y translation
stage
such that each of the nozzles can be placed in an optimal position with
respect to the
mass spectrometer inlet 330 for spraying of the sample material that is
contained
within the microfluidic channel associated with the selected nozzle. The
direction of
the spray is perpendicular to the mass spectrometer inlet 330. In schematic
drawing
of Fig. 10, the nozzles 310 are positioned below the centerline of the mass
spectrometer inlet 330 and the spray is in the direction out of the surface of
the
drawing figure. It will be appreciated that the strips 302 that are still in
tact can be
used in future applications either by using the entire structure of joined
strips 302 or
by detaching one or more strips 302 for use in a given application depending
upon
the precise application and what the requirements for the application are in
terms of
the number of nozzles 310 that is needed.
The microfluidic nozzle array devices disclosed herein are suitable
for use in a number of different types of applications.
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For purposes of illustration only, some of the exemplary applications
will be disclosed with reference to the microfluidic nozzle array device 100
illustrated in Figs. 4-5; however, it will be understood that any of the
devices
disclosed herein can be used in place of device 100.
The microfluidic nozzle array device 100 is particularly suited for use
in nanospray/electrospray applications. Electrospray is the technique that
enables a
liquid sample to be vaporized and ionized for mass spectrometry analysis. The
electrospray process takes place in ambient pressure. Conventional
electrospray
utilizes a capillary with a relatively large inside diameter (i.e., about 50
~,m) to
deliver the liquid sample to the entrance of the mass spectrometer. The liquid
that
is flowing out of the capillary is vaporized under the influence of an
electric field
generated by placing a high voltage (e.g., 4-5 KV) on a metallic conductor
close to
the capillary opening and a ground plane opposite the capillary opening, or
vice
versa. Dry nitrogen flows through concentric tubing to the capillary to help
nebulize the liquid flowing out of the capillary. The flow of the liquid
inside the
capillary is driven generally by a pump, such as a syringe pump.
For the nozzle array of the present microfluidic device 100 to be used
as individual nanospray sources, the reservoir 160 on the opposite side of the
nozzle
opening is filled with a sample to be sprayed. Before the spray, the reservoir
has to
be sealed so that the reservoir is liquid tight. In other words, the open end
of
reservoir 160 (i.e., the open first end 142 of the microfluidic channel 140)
must be
sealed. The sealing of the open end of the reservoir 160 can be accomplished
in a
number of different ways that each provides a satisfactory liquid tight seal
of the
reservoir and permits the sample to be transported within the channel 140.
Figs.
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11-13, illustrate a number of exemplary ways to provide the desired liquid
tight seal
of the reservoir.
For example, Fig. 11 illustrates a first sealing technique in which the
opening of the reservoir 160 (i. e. , the first end 142 of the microfluidic
channel 140)
is sealed with an elastic cover sheet 400. The elastic cover sheet 400 is
preferably
in the form of an elastic polymeric cover sheet. In the microfluidic nozzle
array
device I00, the polymeric cover sheet 400 is coupled to the reservoir wall 124
so
that the polymeric cover sheet 400 extends completely across the open end of
the
reservoir 160. A mechanical plunger 410 or the Iike can be used to apply a
force to
the polymeric cover sheet 400 to force the sample along the length of the
microfluidic channel 140 and ultimately out of the nozzle opening (second end
I44
of the microfluidic channel 140) in a continuous stream, generally indicated
at 430.
The discharged continuous liquid stream of the sample is then vaporized under
the
influence of an electric field. The general direction of movement of the
polymeric
cover sheet 400 and the plunger 410 is illustrate by arrow 420.
Another sealing technique is illustrated in Fig. 12. According to this
technique, a movable sealing member 400 is provided and is formed of a sealing
base 422 for sealing the opening of the reservoir and a rod or plunger 444
that is
attached to the sealing base 442. The dimensions of the sealing base 442 are
greater
than the dimensions of the open end of the reservoir 160 and therefore, the
sealing
base 442 seats against the reservoir wall 124 and completely extends across
the open
end of the reservoir 160. The sealing base 442 is formed of a suitable elastic
material to permit the sealing base to locally deform when a force is applied
thereto.
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This elasticity permits the sealing base 442 to act as a temporary diaphragm
that
seals the reservoir as the sealing base 442 is directed into the reservoir 160
itself.
When the sealing base 442 is pushed downward in the direction
toward the nozzle 170, the sealing base 442 deforms as it is forced into the
first end
of the rnicrofluidic channel 140 (which is also the entrance to the reservoir
160). In
the illustrated embodiment, the sealing base 442 includes a flange 446 that
has a
greater diameter than the diameter of the other portions of the sealing base
and
therefore, when the sealing base is inserted into the reservoir, the flange
446
intimately contacts the inner surface of the reservoir wall 124 and forms the
liquid
tight seal between the sealing base and the reservoir. As the sealing base 442
is
inserted into the reservoir 160 and travels therein toward the nozzle, the
sealing
base 442 effectively forces the sample toward the second end 144 of the
microfluidic
channel 140, causing the sample to be discharged through the nozzle opening
defined thereat. There may be an air gap between the sample (e.g., a liquid)
in the
reservoir 160 and the sealing base 442 or a vent (not shown) can be
incorporated
into the sealing base 442 for air to be pushed out of the reservoir 160 when
the
sample is forced through the microfluidic device by the sealing base 442. The
vent
can be fabricated using conventional vent technology in that the vent should
permit
air passage, while being impermeable to the flow of liquid so that the sample
is
prevented from flowing through the vent and out of the reservoir 160.
It will be appreciated that the plunger 444 can either be manually
operated or it can be part of an automated system including an actuator or the
like
which controls the movement of the plunger 444. All of the plungers 444 can be
linked to a common actuator or the link so that upon activation, the plungers
444 are
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all driven at the same time, resulting in the samples being concurrently
transported
through respective channels to respective nozzles.
Yet another sealing technique is illustrated with reference to Fig. 13
in which a fluid carrying member 450 is provided. The member 450 has a hollow
portion and is generally shaped to be complementary to the shape of the
reservoir
160 to permit the member 450 to seat against the upper edge of the reservoir
wall
124. The member 450 includes a distal end 452 which initially is positioned
proximate to the open end of the reservoir 160. At the distal end 452, a
gasket 460
is provided and in the illustrated embodiment, the gasket 460 is in the form
of a
sealing O-ring or the like. The gasket 460 serves to provide a seal between
the
distal end 452 and the reservoir wall 124 to prevent from escaping between
this
interface when the sample is transported in the following manner. Because the
member 450 is at least partially hollow, the gasket 460 is disposed around the
bore
that extends through the member 450.
In this embodiment, the sample is moved within the microfluidic
channel 140 by conducting a fluid through the member 450 (more specifically,
the
bore thereof) to effectively force the sample through the microfluidic channel
140 to
the nozzle 170 where the sample is discharged in continuous stream 430. The
fluid
is preferably a high-pressure gas, such as air or dry nitrogen gas that is
delivered
from a source that is in fluid communication with the piston bore. The flow
direction of the fluid is generally indicated at 470. In another embodiment,
the fluid
can be the liquid sample fed into the microfluidic channel 140 to continuously
push
liquid out through the nozzle.
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It will be appreciated that a protective cover (not shown) can be
placed at the distal end 452 of the fluid carrying member 450 to prevent
sample
from contacting the inner surfaces of the piston bore. The protective cover
must be
permeable to the fluid that flows through the bore and into the reservoir 160
to
transport the sample along the microfluidic channel 140. For example, the
protective cover can be in the formed of a thin polymeric film that is gas
permeable,
while at the same time being impermeable to liquid flow. In this manner, the
sample can not contact the bore itself. The use of such a protective cover is
not
required since the injected fluid that flows through the member 450 can push
the
liquid sample out by applying a force to the air gap between the sample and
the
surrounding structure.
A more conventional fluid delivery mechanism can be used with the
device 100. In this embodiment, a stopper is inserted into the reservoir 160,
with
the stopper having a bore formed therethrough which is in communication with
the
reservoir 160. A capillary is inserted through the bore and the liquid sample
is
injected into the reservoir through the capillary from a source external to
the
capillary. In this embodiment, the sample is not stored in the reservoir 160
but
rather is delivered to the channel 140 by being injected into the reservoir
160
through the capillary.
As previously mentioned, the front face of the nozzle array is made
electrically conducting by a thin film of metal or conducting polymer. When an
electric field of appropriate strength is applied to the nozzle (e.g., as by
the
arrangement illustrated in Fig. 3), the liquid and the analytes it carries
(i.e., the
sample) are vaporized as they are discharged through the nozzle opening.
Liquids
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that are suitable for use in electrospray mass spectrometry analysis include
but are
not limited to acetonitrile, methanol, ammonium acetate, and other volatile
liquids.
Since the inside diameter of the nozzle is less than about 20 ~,m, the amount
of
material flowing out of the nozzle to be vaporized is less than the amount
that is
typically used in a conventional electrospray operation. Also, the outside of
50 ,um
creates a strong enough electric field for vaporization with applied voltage
below
about 6 KV.
The use of a nebulizing gas to assist in the vaporization process is
therefore not needed; however, if nebulizing gas is needed, channels
conducting dry
nitrogen gas to the nozzle opening may be easily added in a polymer substrate
attached to the front of the nozzle array. Figs. 14-15 are a top plan view and
a
cross-sectional view, respectively, of a rnicrofluidic nozzle array device 500
in
combination with a substrate 510 having gas conduits 520 formed therein for
nebulization. The microfluidic nozzle array device 500 can be similar to or
identical to any of the exemplary microfluidic array devices disclosed
hereinbefore.
A gas outlet 522 is formed such that it is concentric with one nozzle 530. The
substrate 510 with the nebulizing gas channels can be fabricated by an
injection
molding process during the injection molding process that is used to the
nozzle array
device 500 itself or it can be fabricated first and then later attached to
(e.g., bonded)
the nozzle array device 500 as a separate component. The substrate 510 can be
attached in any number of different ways including but not limited to using an
adhesive or meltingly bonding the two members along a boundary zone.
In some instances, it may not be necessary to have the nozzle array
conform to the microtiter plate sample well format. For example, the sample
can be
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fed to the nozzle by the elutant of a high performance liquid phase gas
chromatography (HPLC) column. Since the reservoir size in the nozzle array can
be formed to arbitrary sizes, it can be formed so that the open end of the
reservoir
can receive one end of the HPLC column or any plumbing for splitting the HPLC
elutant for mass spectrometry analysis. The reservoir side of the nozzle array
can
also consist of injection molded features for splitting elutant for mass
spectrometry
analysis. The driving force for the liquid sample analytes to flow through the
nozzle
opening in this case is the pressure-driven liquid flow of the HPLC. Neither a
pressure diaphragm nor an external pressure-inducing mechanism is needed.
The microfluidic nozzle array devices disclosed herein are also
particularly adapted to be used as a nozzle array for optical spectrometry.
Since
each microfluidic channel in the nozzle array device terminates with a nozzle
opening having an inside diameter of 20 ,um or less and the substrate of the
nozzle
array device is formed of a polymeric material which is generally hydrophobic,
liquid inside the microfluidic channel does not drip or be discharged out of
the
nozzle without external force being applied thereto. When light, either
ultraviolet
or visible, is incident on the reservoir side of the array, the light will
come out of
the nozzle opening carrying the optical spectroscopic information of the
analytes
contained within the liquid in the microfluidic channel. The microfluidic
channel
and the nozzle opening thus provide an optical detection system without the
use of
optical windows. This is a significant advantage since the microfluidic nozzle
array
device does not have to be fabricated to incorporate optical windows made of
an
optical material in its design. This results in reduced structural complexity
for the
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microfluidic nozzle array device and also a reduction in both cost and
complexity
relative to the fabrication of the microfluidic nozzle array device.
A 96 microtiter nozzle plate filled with samples can be placed in an
ultraviolet reader for a 96 microtiter plate and spectrophotometric
information for
each sample can be obtained with the reader. A conventional microtiter plate
used
for UV spectrophotometry must have a sample well bottom made of a special UV
transparent material in order to hold the sample inside the well and transmit
UV
light at the same time or a microtiter plate made of quartz must be used. The
use of
a microtiter nozzle plate array plate according to one exemplary embodiment
thus
allows two detection techniques for the samples in the plate without having to
transfer the samples to other additional plates.
Fig. 16 is a cross-sectional view illustrating how the microfluidic
nozzle array device 100 can be used for UV spectrophotometry. Fig. 16
illustrates
the microfluidic nozzle array device 100 in partial section showing two nozzle
structures for purposes of illustrating the use of the microfluidic nozzle
array device
100 in UV spectrophotometry. In this exemplary arrangement, UV light is
emitted
from a source 540 and travels toward the microfluidic nozzle array device 100
and
is incident on the reservoir side 120. The UV light travels through the
reservoir
160 and continues to travel along the length of the microfluidic channel 140,
both of
which hold the sample (e.g., liquid and analytes). The UV light travels
through the
nozzle opening 144 to a detector 550 that is disposed such that it faces the
side of
the microfluidic nozzle array device that contains the nozzles 170. The UV
light
carries the ,spectrophotometric information of the analyte is detected by the
detector
550 of the UV reader. In this manner, the formation of perpendicular
orientated
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microfluidic channels provides advantageously permits UV spectrophotometry to
be
carried out in an easy and convenient manner since the microfluidic nozzle
array
device 100 can easily be disposed between a UV light source and the detector
550 of
the UV reader. Likewise, transmission fluorescence spectroscopy can be carried
out using the microfluidic nozzle array device 100.
Unlike conventional microfluidic devices where optical windows
formed of an optical material were fabricated in the devices, the substrate
body of
the present microfluidic nozzle array device does not have to be formed of an
optically transparent material. This reduces the complexity of the fabrication
process since this requirement is not present in the microfluidic nozzle array
device.
The present microfluidic nozzle array devices disclosed herein also
can be used in a wide range of other applications in which similar
conventional
devices have typically been used. For example, the microfluidic nozzle array
device
can be used for spotting DNA or protein array on a substrate instead of using
the
conventional capillary wicking methods that are now used with metallic
capillaries.
Presently, the DNA array spotting is primarily carried out by "wicking" DNA
fragments into an open split end of a metallic capillary. To spot in an array
format
on a glass slide, the split end of the capillary is pressed slightly onto the
glass slide
by a robotic arm or the like to facilitate the deposition of the DNA
fragments. On
being lifted from the glass slide, the metallic capillary has a tendency to
"spring"
off the glass slide. As a result of this phenomena and other factors, it is
common
that about 20 % of spots in the array are deficient in some way, e. g. ,
either the spot
is bare or an inadequate amount of material has been deposited. Spotting is
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typically carried out with a row of eight to twelve capillaries using an
expensive
machine and the capillaries are rinsed and reused for different DNA samples.
The present microfluidic nozzle array devices disclosed herein have
smaller nozzles openings (e.g., 20 ~,m or less) than conventional nozzle
constructions and a number of advantages can be realized using the present
microfluidic nozzle array devices in comparison to the conventional metal
capillaries. First, the injection-molded microfluidic nozzle array devices can
be
disposed of after each deposition. Thus, the time consuming rinsing process is
eliminated and there is no risk of cross-contamination since the devices are
not
reused. Second, DNA or protein molecules are not adsorbed on the walls of the
polymeric nozzle as they are adsorbed on metallic surfaces. The spotting is
therefore more complete when the molecules leave the polymeric nozzle to be
deposited on the glass slide. Third, a two dimensional nozzle spotter can be
manufactured inexpensively thereby greatly increasing the speed of the
spotting
operation. Fourth, the deposition of the DNA or protein molecules from the
polymeric nozzle can be assisted by pumping the molecules out of the nozzle
with
high pressure air using one of the aforementioned devices and/or with an
electric
field for electrospray.
The microfluidic nozzle array device can also be used for spotting the
plate for matrix-assisted laser desorption ionization (MALDI), replacing the
pipette
and capillary spotting methods. For matrix-assisted laser desorption and
ionization
mass spectrometry, a dominant analytical technique for protein molecules and
fragments of high molecular weight, the molecules to be analyzed are deposited
on a
layer of matrix material, usually LTV-absorbant molecules that can be
vaporized by a
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UV laser. The molecules of interest are thus carried into the gas phase and
are
ionized alongside the matrix molecules. Traditionally, the metallic (usually
aluminum) MALDI plate is spotted manually with the use of micropipettes and
more
recently with capillaries. The efficiency of the ionization process will be
enhanced
if the metallized polymeric nozzles are used for spotting. The matrix material
is
first electrosprayed onto the aluminum MALDI plate which is held at ground
potential, whereas the metal coated nozzle is held at high voltage or vice
versa. The
molecules of interest are then electrosprayed in a new nozzle onto the matrix
material. The spraying allows the matrix molecules and the molecules of
interest to
be more evenly intermingled with one another, thus enhancing the efficiency of
laser
assisted desorption and ionization. The spotting of the MALDI plate may also
be
carried out with a two-dimensional array of nozzles for high throughput. Thus,
the
density of the nozzle array can be greatly increased and this permits the
density of
the spotting array to be increased. Accordingly, more testing or experimental
sites
are provided on the substrate as a result on the increased density in the
spotting. It
will also be appreciated that an electric field can also be used to assist in
the spotting
process. The electric field can be generated by using the arrangement
illustrated in
Fig. 3 or by some other type of suitable arrangement.
One will further appreciate that the manufacturing methods disclosed
herein that are based on injection molding techniques can be used to make
pipette
tips for nano to picoliter dispensing. In other words, a mold can be
fabricated and
resin can be injected into the mold to form pipette tips that have an
elongated body
and terminate in a tip section that has a tip opening having an inside
diameter of less
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than about 20 ~,m (with the tip section having an outside diameter of less
than about
50 Vim.
The following examples serve merely to illustrate several
embodiments of the present microfluidic array devices and do not limit the
scope of
the present invention in any way.
Example 1
A polymeric microfluidic nozzle array device is fabricated using the
technology disclosed herein is by first providing a mold designed for an
injection
mold process. The mold is formed of a metal and a conical surface of the mold
that
defines the nozzle portion of the microfluidic device is polished with a
diamond
paste to form a highly polished surface. More specifically, the conical
surface is
polished with 1 micron diamond particles to provide a close to mirror finish
for the
nozzle that is formed as part of the microfluidic device. The microfluidic
device is
fabricated by injecting polybutyl terephthalate (PBT) into the closed mold and
then
curing the formed structure and then ultimately removing the molded
microfluidic
nozzle array device from the mold. The microfluidic nozzle array device is
formed
to have nozzles that have an average outside diameter of about 60 microns and
an
average inside diameter of the tip (i.e., the diameter of the nozzle opening)
being
less than about 20 microns.
By polishing the conical surface of the mold that defines the nozzle,
the outer surface of the nozzle is made much smoother and further the shape of
the
nozzles is more consistent from nozzle to nozzle and from mold run to mold
run.
By providing a smooth highly polished surface in the conical portion, the
friction of
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the resin flow is reduced and this results in an increase in the accuracy and
efficiency of the injection process. These techniques provide advantages when
forming structures having very small dimensions, such as the nozzles of the
present
microfluidic device which have microscale features.
The microfluidic nozzle array device is then used as an electrospray
device for spraying a liquid sample that is disposed within the microfluidic
features
formed in the microfluidic nozzle array device. As described in detail
hereinbefore,
the nozzle serves to spray the liquid sample into a fine mist through electric-
field
induced evaporation. In this example, a voltage of between 5-6 KV is applied
to a
conductive region formed around the nozzle tip in order to provide the
necessary
electric-field. The vaporized, ionized sample is then injected into an inlet
of a mass
spectrometer for analysis.
Example 2
A polymeric microfluidic nozzle array device is fabricated using the
technology disclosed herein by first providing a mold designed for an
injection mold
process. The mold is formed of a metal and a conical surface of the mold that
defines the nozzle portion of the microfluidic device is polished with a
diamond
paste to form a highly polished surface. More specifically, the conical
surface is
polished with 1 micron diamond particles to provide a close to mirror finish
for the
nozzle that is formed as part of the microfluidic device. The microfluidic
device is
fabricated by injecting polybutyl terephthalate (PBT) into the closed mold and
then
curing the formed structure and then ultimately removing the molded
microfluidic
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nozzle array device from the mold. The microfluidic nozzle array device is
formed
to have nozzles that have an average outside diameter of about 60 microns and
an
average inside diameter of the tips (i. e. , the diameter of the nozzle
opening) being
less than about 20 microns. The mold is constructed so that a microfluidic
nozzle
array strip is formed having two rows of twelve nozzles each.
Upon removing the molded microfluidic nozzle array strip, the above
process is repeated to form one or more other microfluidic nozzle array
strips. The
microfluidic nozzle array strips are then placed side by side and adjacent
strips are
detachably secured to one another by applying an adhesive (e.g., glue) to an
edge of
the each of the strips. More specifically, the edges are heated so that the
polymeric
material softens and then the adjacent strips are joined together along these
edges so
that a fused bond results between the two edges that are brought into contact.
Preferably, the fused bond between adjacent strips includes a weakened section
(e.g., a score line or the like can be formed along the bond or the thickness
of the
bonded interface section between the two strips can be of reduced thickness)
so that
one strip can easily be detached from the other strip. Any remaining
microfluidic
strips are attached in the same manner to form a single, tiled microfluidic
nozzle
array device that contains a weakened section between the adjacent bonded
microfluidic devices. The number of bonded microfluidic nozzle array strips
will
vary depending upon the desired overall size of the microfluidic nozzle array
device
and more particularly, the desired overall number of reservoirs and nozzles
per each
microfluidic device. In use, the single, tiled microfluidic nozzle array
device is
broken apart into two or more sections which can be used or can further be
broken
apart into additional smaller microfluidic devices.
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Example 3
A polymeric microfluidic nozzle array device is fabricated using the
technology disclosed herein by first providing a mold designed for an
injection mold
process. The mold is formed of a metal and a conical surface of the mold that
defines the nozzle portion of the microfluidic device is polished with a
diamond
paste to form a highly polished surface. More specifically, the conical
surface is
polished with 1 micron diamond particles to provide a close to mirror finish
for the
nozzle that is formed as part of the microfluidic device. The microfluidic
device is
fabricated by injecting polybutyl terephthalate (PBT) into the closed mold and
then
curing the formed structure and then ultimately removing the molded
microfluidic
nozzle array device from the mold. The microfluidic nozzle array device is
formed
to have nozzles that have an average outside diameter of about 60 microns and
an
average inside diameter of the tips (i.e., the diameter of the nozzle opening)
being
less than about 20 microns. The mold is constructed so that a microfluidic
nozzle
array strip is formed having two rows of twelve nozzles each.
Upon removing the molded microfluidic nozzle array strip, the above
process is repeated to form one or more other microfluidic nozzle array
strips. Fig.
17 generally illustrates the concept of tiling or otherwise combining a number
of
nozzle subunit structures into a microfluidic nozzle array device of greater
dimension. A base plate 600 is provided and serves as the means for receiving
a
number of nozzle subunits structures, generally indicated at 610, in a manner
in
which the nozzle subunit structures 610 are releasably interlocked with the
base
plate 600. More specifically, the base plate 600 is a frame-like member having
a
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predetermined number of retaining rails 620 that are affixed at their ends to
a pair of
end walls 630. The rails 620 are spaced apart from one another so that open
slots
640 are formed between adjacent rails 620.
As illustrated in Figs. 17 and 18, each rail 620 has a number of
clamping features 650 formed as a part thereof and spaced along the length of
the
rail 620. The clamping feature 650 includes side walls 652 that are spaced
apart
from one another to define a retaining slot 660 therebetween. The side walls
652
are disposed parallel to one another and extend upwardly from a floor 654 of
the
clamping feature 650. The distance between inner surfaces of the side walls
652 is
selected so as to provide a frictional fit between a side wall of the nozzle
subunit
structure 610 so as to secure the structure 610 to the base 600 while at the
same
time permitting the structure 610 to be disengaged and easily removed from the
base
600. Accordingly, the distance between the inner surfaces of the side walls
652 is
equal to or slightly greater than a width of the side wall of the structure
610 that is
received within the retaining slot 660 between the side walls 652.
Alternatively, the entire length of the rail 620 can have a "U-shaped"
cross-section with a retaining slot 660 being formed between two side walls
652 that
are spaced apart from one another. In this embodiment, the entire rail 620
serves as
locking member instead of discrete clamping features 650 that are spaced along
its
length.
In the illustrated embodiment, each nozzle subunit structure 610
includes four nozzles 612 and four reservoirs (not shown) on the opposite side
of the
structure 610. For purpose of illustration only, the nozzles 612 are
illustrated as
facing away from the clamping features 650 (such that the nozzles 612 are in a
plane
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above the clamping features 650); however, the structure 610 can be releasably
interlocked with the base 600 such that the nozzles 612 face in the opposite
direction. In other words, the reservoirs at the opposite end of the
microfluidic
channel face away from the clamping features 650 and are located in a plane
above
the clamping features 650.
The nozzle subunit structures 610 are releasably interlocked with the
base 600 by inserting the two opposing side walls 611 of one nozzle subunit
structure 610 into retaining slots 660 of two adjacent rails 620 that face
another with
an open slot 640 therebetween. One side wall 611 can be inserted first and
then the
~ other side wall 611 can be inserted into the other retaining slot 660 or
both side
walls 611 can be aligned with the slots 660 and then the nozzle subunit
structure can
be pressed downward to effectively dispose the side walls 611 within the
retaining
slots 660. Because both the nozzle subunit structure 610 and the base 600 are
preferably formed of plastic materials and the dimensions of the structures
are
carefully selected, a frictional fit results when the side walls 611 are
received within
the retaining slots 660. When the side walls 611 are received within the
retaining
slots 660, the nozzles 612 and the reservoirs are received within the open
slot 640
such that these elements are not obstructed by the base 600. In other words,
the
reservoir openings are clear so that samples can be injected or otherwise
disposed
within the reservoirs and also the nozzle openings are clear so that the
sample can
be discharged.
In one embodiment, the base 600 is formed of a polymeric material
and is manufactured using an injection molding process such that the base 600
is
formed as a unitary structure. While a frictional fit is one manner of
releasably
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interlocking the nozzle subunit structures 610 to the base 600, a small amount
of
adhesive may be used at the interface between the side walls 611 and the
clamping
features 650 to ensure that the nozzle subunit structures 610 remain in place
during
various applications (when the base 600 may need to be turned upside down,
etc.).
Further, some applications require that a force be applied to the backside of
the
nozzle subunit structure 610 (e. g. , due to actuation of a plunger in the
reservoir,
etc.) and therefore it is desirable for the nozzle subunit structures 610 to
remain in
place and not become dislodged from the base 600 when this force is applied.
Any
number of suitable adhesives can be used and it will be appreciated that one
type of
adhesive is a releasable adhesive that permits the nozzle subunit structure
610 to be
removed from the base 600.
Fig. 19 illustrates another embodiment of base 600 that is very
similar to the configuration illustrates in Figs. 17-1~. In this embodiment,
the
clamping features 650 are configured to receive two side walls 611 of adjacent
nozzle subunit structures 610. Thus, the distance between the inner surfaces
of the
side walls 652 is selected so that the width of two side walls 611 placed in
intimate
adjacent contact with one another is about equal to or slightly less than the
distance
between the inner surfaces of the side walls 652. In other words, the slot 660
is
configured to receive and retain two side walls 611 of adjacent nozzle subunit
structures 610. To removeably couple the nozzle subunit structures 610 to the
base
600 according to this embodiment, one side wall 611 is disposed within the
slot 660
and then another side wall 611 of an adjacent nozzle subunit structure 610 is
disposed in the slot 660 next to the other side wall 611, thereby providing a
frictional fit that results in both adjacent nozzle subunit structures 610
being held
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securely in place. Unlike the embodiment of Figs. 17-18, this embodiment
requires
that the two side walls 611 be disposed within one slot 660 to effectively
couple
each nozzle subunit structure to the base 600.
It will be appreciated that other clamping members can be used
besides the above described ones. For example, each clamping member can
consist
of a spring biased clip that receives side wall 611 in a frictional manner so
as to
retain and hold the side wall 611 in a releasable manner. The clip can consist
of
two opposing plates that are hingedly connected at one end so as to bias the
plates
toward one another. The side wall 611 is received at the opposite ends of the
plates
inserting the side wall 611 between the plates and then directing the side
wall 611
between the plates toward the hinged end. The biasing action between the
plates
ensures that the side wall 611 is securely gripped between the plates, while
at the
same time can be removed by simply overcoming the biasing force and lifting
the
side wall 611 upward until it is free of the plates.
Fig. 20 illustrates yet another base 700 for tiling or otherwise
combining a number of nozzle subunit structures into a microfluidic nozzle
array
device of greater dimension as well as providing a means for increasing the
volume
of the reservoir that forms a part of the microfluidic nozzle array device.
The base
plate 700 is formed of a plastic material and preferably is formed of a
plastic
material that can be injection molded. As previously mentioned, injection
molding
provides a low cost method of forming the base plate 700 without jeopardizing
either the integrity of the base plate 700 or the micro-scale features that
are formed
as part of the base plate 700.
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In this particular embodiment, the base plate 700 resembles a
conventional microtiter plate of a specific format, e.g., a 96-well, on a
surface that
receives the robotic dispensing pipettes. The base plate 700 can be formed to
have a
number of different shapes; however, the base plate 700 generally includes an
upper
face 702 and an opposing lower face 704. The base plate 700 has a number of
open-ended wells 710 formed therein and arranged according to a predetermined
pattern. An upper end 712 of the well 710 defines, in part, the upper face 702
of
the base plate 700, while a lower end 714 of the well 710 is spaced from the
lower
face 704. The well 710 has a tapered construction in that the upper end 712
has a
width that is greater than the lower end 714 of the well 710. It will be
appreciated
that the well 710 can be formed to have any number of different cross-
sectional
shapes and in one exemplary embodiment, the well 710 has a generally annular
shape (i.e., circular cross-section).
The base plate 700 is configured to hold at least one microfluidic
nozzle array device, such as the device 100 illustrated in Fig. 5. For purpose
of
illustration, the base plate 700 will be discussed as being used for holding
device
100; however, it will be appreciated that devices having different features
and/or
configurations can be used so long as the device has retaining features that
permit
the device to be coupled to and retained by the base plate 700. More
specifically,
the device 100 has a number of features formed therein for coupling with the
lower
ends 714 of the wells 710. For example, the first face 120 of the device 100
includes reservoir walls ~ 124 that partially define the reservoir 160. In the
exemplary embodiment, the reservoir wall 124 has an annular shape since the
reservoir 160 itself has such a shape. The first face 120 is configured so
that the
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reservoir wall 124 is raised relative to the surrounding sections of the first
face 120
and therefore, a member can be fitted around the outer surface of the
reservoir wall
124.
The base plate 700 is constructed so that one or more devices 100 can
easily be coupled thereto, resulting in a number of smaller devices 100 being
assembled as a larger grid of devices 100. Such coupling between the devices
100
and the base plate 700 is releasable in nature in that any one of the devices
100 can
easily be removed and/or replaced. To couple one or more devices 100 to the
base
plate 700, each device 100 is positioned so that the reservoirs 160 are
aligned with
the wells 710 formed in the base plate 700. The inner diameter of the lower
end
714 of the well 710 is slightly greater than or about equal to the outer
diameter of
the reservoir wall 124 to permit the lower end 714 of the well 710 to fit
snugly over
the reservoir wall 124, thereby coupling the device 100 to the base plate 700.
The wells 710 are arranged across the base plate 700 so that for each
reservoir 160 there is corresponding well 710 and further there is at least
one well
710 that is aligned with each reservoir 160 of the device 100 when the device
100 is
securely coupled to the base plate 700. Because there is a corresponding well
710
for each reservoir 160 of the device 100, the base plate 700 serves to
actually
increase the volume of the reservoir 160 due to the well 710 acting as an
extension
of the reservoir 160. In other words, the reservoir 160 can be filled through
the
well 710 and any amount of sample that overflows the reservoir 160 is merely
stored in the well 710. As the sample is discharged through the nozzle 170 in
the
manner described hereinbefore, sample from the well 710 is fed into the
reservoir
160 to replace the amount that has been discharged. There is another advantage
to
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the base plate 700 and its ability to increase the effective size of the
reservoir in that
the increased volume of the reservoir behind each nozzle 170 permits the
device 100
to be compatible with and conform with robotic dispensing equipment. This is
illustrated in Fig. 20 which shows that the sample (e.g., liquid) in each well
710 is
held in much higher volume than when only the reservoir 160 of the nozzle
array is
used for holding the sample.
Alternatively, the lower end 714 can interface with the reservoir wall
124 in a different manner in that the lower end 714 can be received within
(between)
the reservoir wall 124. In other words, the outer diameter of the lower end
714 is
selected to be slightly less than or about equal to an inner diameter of the
reservoir
wall 124. In this embodiment, the lower end 714 is snugly received within the
reservoir wall 124 in such a manner that the device 100 is securely coupled to
the
base plate 700.
In both instances whether the lower end 714 is received within the
reservoir wall 124 or the lower end 714 is disposed around the reservoir wall
124,
the joint at the junction between the lower end 714 and the reservoir wall 124
forms
a liquid-tight and air-tight junction for gas over pressure up to a few pounds
per
square inch (psi).
As illustrated in Fig. 20, when the device 100 is coupled to the base
plate 700, the lower face 704 protrudes beyond (e.g., extends below) the
nozzles
170 and has chamfered edges 705 so as to protect the tips of the nozzles 170
without
obstructing the function of the nozzles 170. The lower face 704 should extend
below the nozzle tips to prevent damage to the nozzle tips and to permit the
base
plate 700 to seat against a planar surface as might be the case when the base
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700 is attached to equipment, such as an electrospray device or a
spectrophotometer.
The protruding corners of the base plate 700 also protect the tips of the
nozzles 170
during handling, etc.
In the embodiment where the base plate 700 is to function as an
interface plate for robotic dispensing equipment, the base plate 700 has a
height that
is complementary to the conventional robotic dispensing equipment. According
to
one exemplary embodiment, the base plate 700 includes 96 open-ended wells 710
arranged in the standard x12 grid format. The height of the entire base plate
700
and the nozzle array device 100 can be made to conform to that of the standard
microtiter plate. In this manner, the reservoir volume can be varied and
selected in
view of the given application of the device 100. For example, the base plate
700
and more particularly, the well 710 thereof, can be made so that the combined
volume of the well 710 and the reservoir 160 is about 370 ~,1 as in one of the
standard volumes for a 96 well plate or any other desired volume without the
need
to change the mode design of the nozzle array device 100. In other words, the
effective volume of the reservoir 160 can be varied by varying the dimensions
of the
well 710 as opposed to having to provide different devices 100 having
reservoirs
160 of varying volumes.
Furthermore, a device 100 having a nozzle array with a 3~4 well
spacing can be attached to a 96 well plate attachment if only one our of every
four
nozzles 170 is used to attach to each lower end 714 of the well 710. Thus, not
all of
the wells 710 and/or reservoirs 170 need to be used in any given application.
The
additional advantage of the tiling base plate 700 is that existing
commercially
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available sealing mats and its robotic sealing mechanism can be directly
applied to
the base plate 700 without major modifications.
The upper end 712 of the well 710 is constructed to fit a puncturable
sealing mat 725. The puncturable sealing mat 725 is disposed across the upper
face
of the base plate 700 so that at least the upper ends 712 of the wells 710 are
covered
by the puncturable sealing mat 725. Puncturable sealing mats 725 are known in
the
art and can be obtained from a number of commercial sources. The puncturable
sealing mat 725 is used to prevent evaporation of sample liquid from the well
710
while the base plate 700 is being docked in preparation for transfer to a
piece of
equipment, such as a mass spectrometer, etc.
The base plate 700 thus incorporates open-ended wells 710 that
resemble open-ended tubes and have a first diameter at one end (e.g., lower
end
714) for interfacing with the reservoir wall 124 of the device 100 and a
second
diameter at the other end be selected so that this end has the same opening as
a
conventional well in a microtiter plate 700. The advantages provided by the
base
plate 700 include increased sample storage volume, improved sealing of the
reservoir 160 with commercially available sealing mats, and improved handling
of
the nozzle array devices 100. In addition, the cost of the base plate 700 is
also
relatively inexpensive since the base plate 700 is preferably manufactured by
an
injection molding process.
Fig. 21 illustrates another embodiment for effectively increasing the
volume of the reservoir 160 of the device 100. More specifically, an open-
ended
conduit member 800 is mated with the reservoir wall 124 so as to effectively
increase the volume of the reservoir 160. The conduit member 800 in one
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exemplary embodiment is a piece of tubing that has an open first end 802 and
an
open second end 804. The tubing 800 can be constructed so that it has the same
dimensions along its length or the tubing 800 can be constructed so that one
end
thereof has greater dimensions than the other end. In the latter embodiment,
the
tubing 800 has a tapered construction. Fig. 21 shows the tubing 800 with
slightly
tapered construction with the first end 802 that attaches to the reservoir
wall 124
having smaller dimensions than the second end 804 that is spaced above the
first
face 120 of the device 100.
In one embodiment, the first end 802 has an inner diameter that is
slightly greater than or about equal to an outer diameter of the reservoir
wall 124 so
that the first end 802 can be disposed around the reservoir wall 124 in a snug-
fit
manner (e.g., to provide a liquid-tight and air-tight junction between the
device 100
and the tubing 800). Alternatively, the first end 802 has an outer diameter
that it
slightly less than or about equal to an inner diameter of the reservoir wall
124 to
- permit the first end 802 to be received within the reservoir 160, thereby
securely
coupling the device 100 and the tubing 800.
The tubing 800 can be formed of any number of materials that are
typically used for forming tubing, e.g., plastic materials and rubber
materials. As
with the embodiment illustrated in Fig. 20, the tubing 800 effectively
increases the
volume of the reservoir 160 since the tubing 800 acts as an extension of the
reservoir 160. This provides the advantages that are discussed above in
reference to
the base plate 700.
Fig. 22 illustrates yet another embodiment of a base plate 900 that is
similar to or identical to the base plate 700 in terms of its construction.
The
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difference between the arrangement illustrated in Fig. 22 and the arrangement
illustrated in Fig. 20 is that the base plate 900 configuration is different
from the
nozzle array configuration of the device 100 as opposed to the base plate 700
and
the device 100 configuration which were intended to match one another. For
example, the base plate 900 can be of the 8x12 96 well grid format, while the
nozzle
array devices can have a spacing associated with a 384 well plate spacing. In
other
words, there are more reservoirs 160 than there are wells 710 and therefore,
each
reservoir 160 does not align and match up with a corresponding well 710;
however,
each well 710 preferably is aligned with one reservoir 160. Such a base plate
construction is thus configured to utilize only selected reservoirs 160 as
opposed to
utilizing all of the reservoirs 160 without requiring either the base plate
and/or the
nozzle array device to be custom constructed for a specific application.
The above-described embodiments of Figs. 20-22 provide a nozzle
array that is compatible with microtiter plate formats but has smaller nozzle
array
components and can be used to assemble a number of nozzle array devices in a
tiled
manner. Advantageously, each embodiment provides a means for increasing the
effective volume of the reservoir of the nozzle array device since the well
formed in
the plate is effectively and securely coupled to one end of the reservoir,
thereby
permitting a sample to be injected into the well resulting in sample being
directed
into the reservoir and ultimately into the nozzle tip. By increasing the
effective
volume of the reservoir, the nozzle array device is made more conformant with
robotic dispensing equipment.
Now referring to Figs. 23-30 in which yet another aspect of the
present invention is illustrated. In Fig. 23, a general mass spectrometer set
up is
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generally illustrated and includes a mass spectrometer unit 1000 and a
conventional
electrospray needle assembly 1010 that is used to convert a liquid sample into
a
vapor plume by a technique that is typically referred to as electrospray
ionization
(ESI). The electrospray needle assembly 1010 sprays samples at flow rates that
are
about 5 microliters/minute and higher depending upon the precise application
and
the operating parameters. The electrospray needle assembly 1010 is fixedly
attached to the mass spectrometer unit 1000 to permit the liquid sample to be
ionized
to form the vapor plume which is received in part into an inlet port of the
mass
spectrometer 1000. For example, the mass spectrometer 1000 has an inlet cone
1030 that is configured to receive a portion of the vapor plume that is formed
by the
electrospray needle assembly 1010. The inlet cone 1030 has an inlet opening
extending therethrough which receives the vapor plume.
In electrospray ionization, an analyte solution, is passed, at
atmospheric pressure, through a capillary into a smaller diameter tip 1012
held at a
high potential (e.g., a few KV). The effect of the electric field as the
solution
emerges from the tip 1012 is to generate a spray of highly charged droplets
that pass
down a potential (and pressure) gradient towards an analyzer, which in this
case is
the mass spectrometer unit 1000. The tip 1012 is typically spaced from the
inlet
cone 1030 and is arranged so that the opening formed through the tip 1012 is
not
axially aligned with the opening formed through the inlet cone 1030. Instead,
the
tip 1012 is arranged that its longitudinal axis is normal to an axis through
the
opening of the inlet cone 1030. Further, the opening formed through the tip
1012
and the inlet opening formed through the inlet cone 1030 typically lie in the
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plane when the electrospray needle assembly 1010 is fixed in place relative to
the
mass spectrometer unit 1000.
Electrospray ionization is highly inefficient since it is characterized
by relatively high flow rates of the analyte solution in order to provide
enough
sample to be received within the inlet cone 1030 to permit the mass
spectrometer
unit 1000 to function properly. For example, it is commonplace for only about
4%
of the sprayed analyte solution to be captured within the inlet cone 1030 and
because
of the high sample flow rates of the analyte solution in electrospray
ionization
applications, this results in a significant quantity of sample being wasted.
Because of the aforementioned and other deficiencies, nanospray has
and is increasingly becoming an attractive alternative to electrospray
ionization.
Nanospray is the technique used in mass spectrometry to convert a liquid
sample
into a vapor plume using substantially less sample as compared to conventional
electrospray ionization. As previously- mentioned, flow rates of the sample
through
the nanospray nozzle is typically well under 1 microliter/minute. However,
there
are a number of disadvantages that must be overcome in order to realize the
benefits
of nanospray. For example, one of the difficulties that is encountered when a
user
wishes to use the mass spectrometer unit 1000 for both nanospray and
electrospray
applications is that existing apparatuses for use with nanospray devices
require the
user to remove the conventional ESI fixture and insert the selected nanospray
apparatus in its place. In other words, the conventional electrospray needle
assembly 1010 must be detached from the mass spectrometer unit 1000 to permit
the
nanospray apparatus to be fixed to the same framework that supports the
electrospray needle assembly 1010. This is a very time consuming task since
each
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assembly is , typically bolted to a frame, that supports the mass spectrometer
unit
1000 and therefore, the removal of one assembly requires the user to unbolt
the
assembly and bolt the other in place. The amount of time required for set-up
and
performing the analysis must factor in the time required to make sure that the
correct equipment is in place and this can require the above
unbolting/rebolting
steps. Moreover, such an arrangement precludes the use of a "universal"
nanospray
apparatus that can be used in a mass spectrometer unit of different makes
since the
nanospray apparatus has to be bolted onto the frame work of the mass
spectrometer
unit.
As best shown in Figs. 24, 25, 29 and 30, in order to overcome the
above disadvantages and permit the changing from ESI to a nanospray
application to
be a much easier task and far less time consuming, a universal holder device
1100 is
provided. The holder device 1100 is intended to be used with a nozzle array
device
of a given size, such as the nozzle array device 100 and includes a frame 1110
that
receives the device 100. As described in great detail hereinbefore, the device
100 is
in the form of a small plastic chip that includes an array of nozzles formed
therein.
The frame 1110 is preferably formed of a plastic material and has an opening
1112
formed therein that is complementary in shape and size to the outer periphery
of the
device 100 so that the device 100 is disposed within opening 1112 in such a
manner
that there are no spaces or very little space formed between the device 100
and the
frame 1110. Preferably, the dimensions of the device 100 and the opening 1112
are
such that a close frictional fit results between the device 100 and the frame
1110. In
addition, a coupling assisting agent, such as an adhesive (glue), etc., can be
used to
ensure that the device 100 remains securely held in place within the opening
1112 of
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the frame 1110. In one exemplary embodiment, each of the device 100 and the
frame 1110 is either square shaped or rectangular shape.
It will also be appreciated that the device 100 and the frame 1110 can
be made as a single integral part as by a common injection molding process.
This
would eliminate the steps of disposing the device 100 within the frame 1110
and
making sure that the two are securely coupled to one another.
As illustrated in Figs. 23, 24, and 30, the holder device 1100 also has
a holder 1120 for holding the frame 1110 securely in place so that the device
100
can be properly aligned with the mass spectrometer unit 1000 and more
specifically,
the inlet cone 1030. The holder 1120 can have any number of different shapes
so
long as the holder 1120 includes a planar platform 1130. According to one
exemplary embodiment, the holder 1120 is generally L-shaped in that it
includes a
support section 1132 that intersects and is integral to one end of the planar
platform
1130. The support section 1132 and the planar platform 1130 are thus arranged
at a
right angle with respect to one another to give the holder 1120 a generally L-
shaped
construction. In one exemplary embodiment, the holder 1120 is formed of a
single
piece of plastic, such as a plexiglass material or the like.
The planar platform 1130 is connected to the support section 1132 at
a first end 1134 thereof, with a second end 1136 being where the device/frame
combination is secured and held in place. More specifically, at or near the
second
end 1136, first and second retaining members 1140, 1142 are spaced apart from
one
another to form a space 1144 therebetween for receiving the frame 1100. The
first
and second retaining members 1140, 1142 can comprise any number of different
types of members that are constructed fox engaging and holding a member
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therebetween. For example and according to one exemplary embodiment, the first
and second retaining members 1140, 1142 are merely elongated rails that are
formed as part of or secured to an upper surface of the planar platform 1130.
The
rails 1140, 1142 are disposed parallel to one another so that a parallel slot
or space
1144 is formed therebetween. The dimensions of the space 1144 are
complementary to the dimensions of the frame 1100 so that the frame 1100 can
be
received and held within the space 1144. For example, the width of the space
1144
can be about equal to or even very slightly less than the width of the frame
1100 so
that a secure frictional fit is formed between these components when the frame
1100
is disposed in the space 1144. It is intended for the holder 1120 to be reused
with
other frames 1100 and therefore, the frame 1100 should be able to be removed
from
the holder 1120 to permit the user to insert and secure another frame 1100
between
the rails 1140, 1142.
When the device 100 is securely held in place between the rails 1140,
1142, the device 100 is in a vertical orientation relative to the planar
platform 1130.
In other words, the device 100 is upwardly standing between the rails 1140,
1142.
The rails 1140, 1142 have a height that does not interfere with spraying of
sample
through the nozzles that are formed as part of the device 100. Thus, the rails
1140,
1142 typically do not extend beyond a lowermost edge of the frame 1100 and
therefore they do not obscure the lowermost nozzles. The length of the
illustrated
rails 1140, 1142 is such that they do not extend beyond the ends of the frame;
however, this is not critical and the opposite configuration is equally
applicable.
As best shown in Figs. 24, 25 and 30, the frame 1100 also preferably
has a locating and retaining feature that is formed as part of one or more
faces of the
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frame 1100. In one exemplary embodiment, one face of the frame 1100 includes
four posts 1160 that are spaced in each of the corners of the frame 1100. The
illustrated frame 1100 is generally square shaped and therefore the distance
between
any two posts 1160 is approximately the same. Two of the posts 1160 act as
locating and retaining features by engaging one of the rails 1140, 1142. More
specifically, the two bottommost posts 1160 are formed on the frame 1100 and
spaced apart from one another such that one of the rails 1140, 1142 is
received
between the bottommost posts 1160 in a frictional manner so as to locate and
further
secure the frame 1100 to the holder 1120 by locking the frame 1100 in place.
Each
of the posts 1160 has a sufficient height so that the post 1160 can engage one
of the
rails 1140, 1142 in a manner that limits the lateral movement of the frame
1100. In
other words, if the user tries or accidentally applies a lateral force to the
frame
1100, the posts 1160 prevent the frame 1100 from moving in the lateral
direction.
Thus, in order to place the frame 1100 within the holder 1120 or remove it
therefrom, the user must press the frame 1100 downward or lift it while the
respective rail 1140, 1142 is positioned between the posts 1160. The posts
1160
also serve to protect the nozzles 150 in case the device 100 falls upside down
such
that the face having the nozzles 150 extending outwardly therefrom is the
ground
contacting surface. Without the posts 1160, the tips of the nozzles 150
represent the
bottommost points of the device 100 and therefore, these tips will strike the
surface
and likely become damaged and/or destroyed. With the posts 1160, the posts
1160
represent the bottommost points of the device 100 and will therefore strike
the
ground first instead of the nozzle tips striking the ground. In this manner,
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1160 serve to protect the nozzles 150. Thus, the lengths of the posts 1160
must be
greater than the height of the nozzles 150.
The frame 1100 also includes a tab 1101 for handling thereof as
shown in Figs. 24 and 25. For example, the tab 1101 extends outwardly from one
edge of the frame 1100 and permits a member for the user to easily grasp when
the
user is either inserting or removing the frame 1100 into or out of the holder
1120.
The tab 1101 is thus positioned on the top edge of the frame 1100 when the
frame
l I00 is inserted into the holder 1120 to permit the tab 1101 to be easily
accessible to
the user. Thus, the user will grip the frame 1100 by the tab 1101 when the
user
lowers the frame 1100 into the holder 1120 and conversely, the user grips the
tab
1101 to remove the frame 1100 from the holder 1120. While the illustrated tab
1101 has a square shape, the tab 1101 can have any other number of shapes,
such as
oval, triangular, irregular shape, etc.
The remaining part of the planar platform 1130 can be used as a
support surface to hold other components that can be used in various nanospray
applications. For example and as will be described in greater detail
hereinafter, the
planar platform 1130 can support a capillary device 1300 (shown in the
embodiment
illustrated in Fig. 30) that is used to ionize and inject the sample into the
reservoirs
160 of the various nozzles 150 of the device 100.
In the event that the holder II20 is to be rigidly connected to the
frame work that supports the other components of the mass spectrometer unit
1000,
the holder 1120 is constructed and positioned so that when the frame 1100 is
securely held between the rails 1140, 1142, at least one nozzle 150 of the
nozzle
array is designated as the target nozzle that is positioned in proximity to
the inlet
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cone 1030 of the mass spectrometer unit 1000 for injecting sample therein. The
precise location of the device 100 is variable so long as a sufficient amount
of
sample that is injected into the nozzle 150 is transferred into the inlet cone
1030.
For example, in the embodiment shown in Fig. 23, the axis through the tip
opening
formed in the nozzle 150 is normal to the axis through the inlet cone 1030
similar to
the way the conventional electrospray apparatus is arranged; however, it is
not
necessary for the nozzle tip opening to the be in the same plane as the
opening
formed in the inlet cone 1030. In contrast, the device 100 can be locked into
holder
1120 so that the nozzles 150 are positioned slightly above the iuet cone 1030
(with
the axis of the nozzle tip opening being normal to the axis of the inlet cone
1030).
In other words, Fig. 23 is an example of an arrangement of the nanospray
apparatus
in the source region of the mass spectrometer unit. The nanospray apparatus is
positioned such that the nozzles 150 point toward the inlet cone 1030. The
substantially smaller amount of sample sprayed by the nanospray nozzle 150
than
that of ESI makes it possible for the spray to point at the inlet cone 1030
without
overwhelming the mass spectrometer unit 1000 with vapors. Fig. 29 shows an
alternative arrangement where the axis through the nozzle opening is parallel
to and
in some cases axially aligned with the axis through the opening of the inlet
cone
1030.
The present nanospray apparatus, including the holder 1120, accesses
the source region of the mass spectrometer unit 1000 through a cut-out in the
clear
cover that surrounds the source region. For different makes of mass
spectrometer
units 1000, different covers with appropriate cut-outs will have to be
fabricated to
replace the original covers. However, one will appreciate that it is possible
to
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operate mass spectrometers without surrounding the source region with a cover,
but
it is generally preferred to have the cover because of the presence of high
voltage
and relatively high temperatures in the source region.
As shown in Fig. 30, it is also preferred for the nanospray apparatus
to be coupled to an automated positioning system 1400 that permits the
nanospray
apparatus to be easily brought into the proper position with respect to the
mass
spectrometer unit 1000. More specifically, the system 1400 is preferably an
automated robotic system that is movable in the x, y, and z directions so as
to at
least permit the selected nozzle 150 of the nozzle array to be adjusted with
respect to
the position of the inlet cone 1030.
There are a number of robotic systems 1400 that are commercially
available and are suitable for use in the present invention. Typically, the
robotic
system 1400 has at least an x, y, z coordinate drive system so that the device
100 is
adjusted until optimum x, y, z coordinates are determined and then stored
within the
programmable system. Because the device 100 has a number of nozzles 150 that
can be used for a given experiment or application, the system 1400 maps the x,
y, z
coordinates of the nozzles 150. This can be based on user inputted
information,
such as the nozzle array size. For example, if a device 100 having 96 nozzles
150
arranged in an 8x12 grid is selected, then the user inputs the grid array size
(8x12)
into the user interface (e.g., a personal computer, etc.) of the robotic
system 1400
and a coordinate map is generated indicating the relative coordinate positions
of all
of the nozzles 150. The robotic system 1400 can receive other information
concerning other parameters or characteristics of the overall system,
including the
type of mass spectrometer unit 1000, etc., and optimum x, y, z coordinates for
the
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spraying nozzle 150 (one of the nozzles in the array) are determined and the
robotic
device 1400 moves the device 100 so that the spraying nozzle 150 is set at the
optimum coordinates.
As soon as the spraying nozzle 150 has performed the spraying
operation, the robotic system 1400 moves the device 100 so that another one of
the
nozzles 150 is disposed at the optimum x, y, z coordinates. Thus, each nozzle
150
is set at the optimum x, y, z coordinates when the spraying operation is
performed
and this results in a sufficient amount of sample being injected into the
inlet cone
1030 for each spraying operation. In one exemplary embodiment, the robotic
system 1400 has a base that is movable at least in two directions by being,
for
example, guided along guide rails, etc., and a robotic arm or the like is
connected to
the base and is likewise movable in one or more directions. Preferably, the
robotic
arm is movable in a number of directions and one end of the support section
1132 is
connected to the robotic arm so that the holder 1120 is supported by the
robotic arm
and therefore movement of the robotic arm is directly translated into movement
of
the holder 1120.
Determining the optimum x, y, z coordinates depends upon a number
of different parameters so that the goal of having a full plume spray can be
achieved. Several of these parameters including, the properties of the
electrospray
and the diameter of the nozzle tip opening, and the user preferably observes
the
mass spectrometer unit 1000 as the user injects the liquid sample. By varying
the
applied voltage, the plume profile of .the sample liquid can be varied and
therefore,
by varying any of the above parameters as well as others, the plume of the
liquid
sample can be varied to ensure that a sufficient quantity of liquid sample is
injected
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into the inlet cone 1030. While the device 100 can be arranged above the inlet
cone
1030 with the individual nozzles 150 facing downward towards the inlet cone
1030
(see Fig. 23), the device 100 can be arranged such that the axis through the
nozzle
opening is axially aligned with the axis through the inlet cone 1030 (see Fig.
29). In
this embodiment, the nozzle tip is spaced away from the opening in the inlet
cone
1030 to permit a sufficient quantity of the ionized sample to the injected
into the
opening extending through the inlet cone 1030.
As best illustrated in Figs. 26-28 and 31-32, according to one aspect
of the present invention, the frame 1100 is metallized in selected regions and
an
inner surface of at least one of the rails 1140, 1142 is metallized so that an
appropriate voltage potential (e.g., ground potential in one example) is
applied to
the frame 1100 of the device 100 when the frame 1100 is disposed within the
space
1144 between the rails 1140, 1142. The high voltage needed for spraying may be
likewise applied to the liquid in the nozzle 150 through a metallized path
from the
reservoir 160 behind the nozzle 150 to the inside surface on the other side of
the
space 1144 or the high voltage can be applied through a discrete electrode
placed
inside the reservoir 160 behind the nozzle 150.
For example, Figs. 26-28 and 3I-32 illustrate an embodiment where
an inner surface of one rails 1140, 1142 is metallized and a conductive,
metallized
pathway is formed on frame 1100 and the device 100 to serve either as a means
for
grounding the device 100 or as a means for applying high voltage to the device
I00
so as to permit a nanospray application to be performed. A first conductive
pathway (electrical pathway) 1143 is formed on the planar platform 1130 and
includes a first end 1145 and a second end 1147 that terminates at the rail
1140 and
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is in electrical contact with the conductive material on the inner surface. A
second
conductive pathway (electrical pathway) 1151 is also formed on the planar
platform
1130 and includes a first end 1153 and a second end 1155 that terminates at
the rail
1142 and is in conductive contact with the conductive material on the inner
surface.
Preferably, the first conductive pathway 1143 is formed along one side edge of
the
planar platform 1130 and the second conductive pathway 1151 is formed on the
opposite side edge of the planar platform 1130. Each of the first ends 1145,
1153
can terminate in a contact pad or an enlarged region that is adapted to
connect to
either a high voltage source or ground. The first and second conductive
pathways
1143, 1151 can be formed using any number of conventional techniques,
including
using a printing process to lay down a conductive material according to the
defined
pathway. Because one of the pathways 1143, 1151 serves as a high voltage
pathway
and the other pathway 1143, 1151 serves as a ground pathway and therefore the
two
pathways cannot intersect.
In one embodiment, the conductive, metallized path extends from an edge
of the frame 1100 and across the device 100 to the reservoir behind the nozzle
150
for applying high voltage to the liquid behind the nozzle 150 to ionize the
sample as
it passes through the nozzle 150. Each nozzle reservoir 160 can have its own
associated metallized path that leads to the edge of the frame 1100 such that
when
the frame 1100 is disposed within the space 1144, the metallized paths formed
at the
edge of the frame 1100 is placed in electrical contact with an inner
metallized
surface of one of the rails 1140, 1142. Alternatively, some branching of the
metallized paths is provided so that one metallized line at the edge of the
frame 1100
can branch into two or more metallized lines that lead to two or more
reservoir 160.
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This type of arrangement is advantageous when there is a need to energize a
group
of nozzles in a specific pattern simultaneously, or when there are a
significant
number of nozzles 1S0 such that if each reservoir 160 associated with each
reservoir
had its own associated metallized line that extended to the edge of the frame
1100,
S there would be significant crowding of metallized lines at the edge of the
frame
1100. The metallized surface of the respective rail 1140, 1142 is then
operatively
connected to a high voltage source and the other of the rails 1140, 1142 is
grounded
by any number of conventional techniques, including forming a metallized
surface
on this other rail 1140, 1142 and connecting this metallized surface to
ground. It
will also be appreciated that the other rail 1140, 1142 does not have to
include a
metallized inner surface to provide a ground since there are number of other
ways to
provide a ground. For example, the proximity between the device 100 and the
inlet
cone 1030 permits the inlet cone 1030 to serve as a ground without the inlet
cone
1030 being in contact with the frame 1100.
1S The amount of conductive material disposed on the one or more inner
surfaces of the rails 1140, 1142 and the precise pattern thereof can vary from
application to application. For example, the precise pattern of the conductive
material on each rail 1140, 1142 will depend upon the pattern of the
conductive
pathways formed on the frame II00. In other words, the two conductive surfaces
must mate with one another to provide an electrical pathway therebetween.
Figs.
26-27 illustrate the holder 1120 without the device 100 being disposed
therein, while
Fig. 28 illustrates the holder 1120 having the device 100 securely held
between the
rails 1140, 1142. Fig. 28 also illustrates how the posts 1160 positioned on
either
side of the front rail 1140 prevent lateral movement of the device 100.
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Alternatively, neither the frame 1000 nor the inner surfaces of the
rails 1140, 1142 has a conductive, metallized coating but rather a wire or the
like
can be directly inserted into the liquid sample that is disposed within the
reservoir
160. The other end of the wire is connected to a high voltage source and when
actuated, the liquid sample is subjected to high voltage conditions through
the wire
and this serves to ionize the liquid sample as it passes through the nozzle
150 from
the reservoir 160 to the tip opening. The frame 1100 can be grounded using any
number of techniques, including the inlet cone 1030 acting as the ground for
the
device 100 due to its proximity thereto.
Fig. 29 illustrates a nanospray device interface 1600 in combination
with the mass spectrometer unit 1000. A mounting mechanism 1610 with x, y, and
z translational movement, such as the positioning system 1400, is provided and
the
holder 1120 is securely attached thereto. In this embodiment, the holder 1120
has
electrical contacts, such as the conductive pathways 1143, 1151, formed
thereon.
The holder 1120 is supported at least in part by the mounting mechanism 1610
and
therefore, the translational movement of the mounting mechanism 1610 is
translated
to movement of the holder 1120.
A cover 1620 of the mass spectrometer unit 1000 is disposed around
the inlet cone 1030 and the frame 1100 to function in the manner described
hereinbefore. In this embodiment, the device 100 is vertically orientated and
is
disposed across from the inlet cone 1030 with the target nozzle 150 being
positioned
so that a sufficient quantity of the ionized spray is directed into the
opening formed
through the inlet cone 1030.
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t
Furthermore, in another embodiment illustrated in Figs. 24, 25 and
30, a metallized capillary 1300 is used and a metallized tip portion thereof
is
disposed within or in close proximity to the reservoir 160. The capillary 1300
serves to inject the liquid sample into the reservoir 160 and high voltage is
applied
to the conducting sections through a metallic or other conductive coating on
the
capillary 1300 and this results in the injected sample being charged. When the
liquid sample flows out of the capillary into the microfluidic channel into
the nozzle
150 it becomes charged when it comes into contact with the conducting coating
held
at high voltage at the opening of the capillary. When a metallized or
conducting
capillary 1300 is used, the capillary 1300 can be supported by a capillary
holder
1310 (parallel to the microfluidic device 100) that is connected to the planar
platform 1130 of the holder 1120 and liquid sample is injected into the
capillary
1300 in a traditional manner and the metallized sections of the capillary 1300
are
operatively connected to a high voltage source. When a metallized capillary
1300 is
used, the device 100 does not have to have any rnetallized paths formed
therein
since the high voltage source is connected to the capillary 1300 and not the
device
100.
Figs. 3I-32 illustrate an embodiment where the nozzle device 100 and
frame 1100 have electrical pathways (electrode placements) formed thereon.
Fig.
31 is a top view of the reservoir side of one exemplary embodiment where the
device 100 is disposed within the frame 1100 that includes the tab lIOI for
easy
handling of the frame 1100. In the exemplary embodiment, the device 100
includes
.four nozzles 150 with their corresponding reservoirs. A pair of outer
conducting
pathways 1181 is formed across the device 100 and the frame 1100 and more
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specifically, the outer conducting pathways 1181 extends along two edges 1183,
1185 of the device 100. One end of the outer conducting pathway 1181
terminates
at or near the entrance to the microfluidic channel connecting the reservoir
160 to
the nozzle 150 and the other end of each pathway 1181 extends from edge 1187
and
across the frame 1100 to a conducting tab 1191 formed at an edge of the frame
1100. The conducting tab 1191 preferably has greater dimensions in comparison
to
the pathway 1181 so that the conducting tab 1191 is in the form of an
increased area
of conductive material for making electrical contact with one or more
electrodes
formed as part of the device holder 1120. The conducting pathways 1181 and the
conducting tab 1191 can be formed of any number of suitable conductive
materials,
such as a noble metal film or other material that can be printed on the
surfaces of
the device 100 and the frame 1100 according to desired patterns.
A pair of inner conducting pathways 1193 is formed across the device
100 and the frame 1100 similar to the outer conducting pathways 1181 but in
different locations thereof. More specifically, the outer conducting pathways
1181
extend from the other two reservoirs 160 to the edge 1187 and are formed
between
the two outer pathways 1181. Similar to the outer conducting pathways 1181,
each
of the inner conducting pathways 1193 terminates at or near the entrance to
the
microfluidic channel formed through one reservoir 160 and the other end of
each
pathway 1193 extends from edge 1187 and across the frame 1100 to a conducting
tab 1191 formed at an edge of the frame 1100. Because the reservoirs 160 that
are
associated with the inner conducting pathways 1193 are closer to the edge
1187, the
lengths of the inner conducting pathways 1193 are less than the lengths of the
outer
conducting pathways 1181. Also, each outer conducting pathway 1181 has a
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relatively long linear section formed along one of the edges and in a manner
such
that it does not interfere with the other reservoirs 160. In this embodiment,
there
are four conducting tabs 1191 formed along the edge of the frame 1100, one for
each conducting pathway that is associated with one reservoir 160. The tabs
1191
are spaced apart from one another; however, the precise spacing and
arrangement of
the tabs 1191 are not critical and are more a matter of design choice.
Fig. 32 is a sectional view through one nozzle 150 of the device 100
according to another embodiment. As shown, the device 100 includes the nozzle
150 and the reservoir 160. According to one embodiment, a capillary 1195 is
provided for pumping liquid sample into the nozzle 150. The capillary 1195 is
connected to a source of the liquid sample at one end thereof, while the other
end is
disposed through the microfluidic channel 30 formed through the nozzle 150.
The
capillary 1195 has a conductive coating 1196 disposed on a section thereof and
preferably, the conductive coating 1196 is formed along an outer surface of
the
capillary 1195 from a point inward from a distal end 1197 to the distal end
1197
itself where the capillary 1195 enters the microfluidic channel behind the
nozzle
150. In other words, the conductive coating 1196 is formed along a distal
section of
the capillary 1195. The capillary 1195 also includes an electrical contact
1198 that
is electrically connected to a high voltage source. The electrical contact
1198
connects to the capillary 1195 at a point along the conductive coating 1196 so
that
an electrical connection can be established between the high voltage source
and the
capillary 1195 and the conductive coating 1196 provides a conducting pathway
for
the high voltage. Preferably, the diameter of the microfluidic channel 30 is
about or
equal to the outside diameter of the conductor-coated capillary 1195 to ensure
a
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liquid tight seal when the capillary 1195 is disposed through the back of the
reservoir 160 and into and through the nozzle 150 to the nozzle tip thereof.
By
flowing liquid sample through the capillary 1195 while simultaneously applying
high
voltage to the conductive coating 1196 through the electrical contact 1198,
the liquid
sample can be vaporized and ionized for a nanospray application.
Fig. 33 illustrates a microfluidic device 1800 according to yet another
aspect of the present invention. The microfluidic device 1800 is very similar
to the
device 100 and therefore, only the differences between the two devices are
described as follows. The microfluidic device 1800 is therefore a microfluidic
device formed of a plastic material that has been injected molded to form a
structure
having an array of nozzles formed as part thereof. In contrast to the device
100, the
device 1800 is formed so that one reservoir 160 can feed two or more nozzles
1810.
More specifically, each reservoir 160 has a base floor 1820 that is actually
the
interface between the reservoir 160 and the two or more nozzles 1810. The base
floor 1820 is preferably a planar floor and it includes a number of openings
formed
therein which each represents an entrance into one of the nozzles 1810. Each
nozzle
1810 is formed of a microfluidic chamiel section 1812 that tapers inwardly at
a
distal end to define a nozzle tip 1814 that terminates in a nozzle opening
1816. The
nozzle openings 1816 thus are openings that are formed along one face of the
device
1800 while the other face include much larger openings that represent the
entrances
to the reservoirs 160.
Preferably, each nozzle opening 1816 has a diameter between about
20 to about 50 microns and the nozzle openings 1816 can be arranged in a
regular
or irregular format with spacing between the nozzle openings 1816 being
preferably
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greater than 50 microns to about several hundred microns or more. In the cross-
sectional view of Fig. 32, there are a number of nozzles 1810 arranged in a
linear
manner, e.g., along rows, etc. It will be appreciated that the device 100 can
be
constructed to include only one reservoir 160 with a plurality of nozzles 1810
being
in fluid communication with the one reservoir 160 so that the one reservoir
feeds the
plurality of nozzles 1810 with liquid sample.
In yet another aspect of the present invention, an improved process
for spraying a liquid from droplets to a vapor plume using a polymeric nozzle
array
device, such as device 100, is provided. Spraying a liquid through a
constricted
opening with the aid of an electric field is widespread process for generating
a vapor
plume for a variety of applications. In the application fox mass spectrometry,
the
vapor plume carrying the ions of the molecules of interest is directed into
the mass
spectrometer unit 1000 where the masses of the ions of the molecules are
obtained.
From the mass of the molecule, the chemical nature of each molecule is
obtained.
In the prior art, the electric field large enough to create the vapor plume is
provide
by the small radius of the constricted opening, or nozzle because the electric
field at
the nozzle is inversely proportional to the radius of the nozzle. Some
examples of
such nozzle devices are a glass capillary wide one end tapered to less than 30
microns in diameter and an outer surface at the tapered end metallized to act
as an
electrode and microfabricated silicon nozzles that have an outside diameter of
35
microns. In the case of silicon nozzles that axe fabricated on a planar
substrate, the
outside surface of the nozzle 150 is held at ground potential, and the liquid
sample
coming through the nozzle is charged at high voltage. Since the wall of the
nozzle
150 can have a thickness of about 12.5 microns, the electric field generated
by the
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distance between the charged liquid and the ground potential of the outside
wall of
the silicon nozzle (i.e., the distance of about 12.5 microns), generates an
additional
field that is comparable in strength as the electric field generated by the
nozzle
diameter. In both of these instances, the physical dimension of the nozzle
radius is
critical in determining whether the electric field strength generated by a
given
applied voltage is sufficient to cause the liquid to vaporize into a plume.
The disadvantages of the above processes are that (1) the outside
diameter of the nozzle 150 must be made very small, i.e., under 35 microns,
which
requires expensive manufacturing process such as microfabrication technology
involving photolithography and reaction ion etching or laser pulling that can
crease
one nozzle 150 with each pull; (2) when the outside diameter of the nozzle 150
is
restricted to below 35 microns, the inside diameter of the nozzle 150 is
necessarily
also small, less than 10 microns; and these inside diameter are conducive to
clogging of the nozzles by liquid samples that have many large molecules
suspended
in them; and (3) the small outside diameter of the nozzle also makes the
nozzle
fragile and easily damaged through routine handling.
The present process is suitable for using the polymeric nozzle device
100 for spraying a liquid through the nozzle 150 in the form of droplets, a
vapor
plume or multiple vapor plumes with a voltage applied to the liquid. The
liquid
placed behind the nozzle 150 is pumped through the nozzle 150 by liquid or gas
pressure means, while a sufficiently high voltage typically in the range of
about ~ 1
to 3.5 KV is applied to the liquid placed behind the nozzle 150 through an
electrode
which may be inserted into the space (e.g., reservoir 160) behind the nozzle
150, or
may be a built-in electrode made by depositing a film of noble metals, such as
gold,
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into the area behind the nozzle 150 where the liquid sample will come into
contact
with the electrode before emerging from the nozzle opening. As the liquid
emerges
from the nozzle opening, the very tip of the liquid, known as the Taylor cone,
under
the influence of the electric field created at the tip of the liquid, will
spray outward
from the nozzle opening. As the applied voltage is increased, the form of
spray
changes from large liquid drops several hundred microns in diameter to a mist
of
fine droplets or vapors. For mass spectrometry analysis, the spray with the
fine
droplets or vapor is preferred. The ions bound in each droplet are released
from the
fine liquid droplets when the liquid in the droplets has evaporated with or
without
the assistance of a desolvation gas, typically nitrogen gas flowing into the
plume
droplets from the opposite direction as the droplets. The ions then enter the
mass
selector of the spectrometer to be analyzed.
There is an alternative process to operate the nozzle device to obtain
ions from a liquid sample for mass analysis. In the aforementioned process,
the
liquid sample is continuous pumped through the nozzle opening while a high
voltage is applied to the liquid sample to obtain a spray of fine droplets. In
the
alternative process, the liquid sample placed inside the microfluidic channel
behind
the nozzle is not pumped through the nozzle, i. e. , the flow-rate of the
liquid through
the nozzle is zero. A high voltage is applied to the said liquid sample
through the
conducting end of the capillary as depicted in Figure 32. The electric field
acting
on the droplet of liquid in the microfluidic channel causes the vaporization
and
ionization of the liquid sample. The ions formed during this process do so
without
being bound to a large number of sprayed liquid droplets. These ions thus
formed
leave the microfluidic channel through the nozzle opening 150 and move toward
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low potential on the reference electrode at the inlet of the mass spectrometer
to be
analyzed. In this manner, less than 200 nl of sample initially stored inside
the
microfluidic channel may generate enough ions continuously for mass
spectrometry
analysis for over twenty minutes. This mode of operation is especially
valuable
when only nanoscale amount of sample that needs high degree of accuracy of
analysis through prolonged measurements is available for measurements.
In the prior art, there is an analogous mode of nanospray that is
achieved without any external pumping means for the liquid sample in a
capillary
tube which is tapered at the spraying end to an extremely small opening,
typically
several microns in diameter, , t The use of such small tapered ended capillary
tubes
creates a number of difficulties since these tapered ends are very delicate
and
susceptible to breaking and damage. Loading the liquid sample into such a tube
is
very cumbersome accordingly. In addition, the small tapered opening in the tip
thereof is prone to clogging. In the present disclosed process, the liquid
sample
stored inside the microfluidic channel may be placed there with the aid of
robust
methods such as a robotic liquid dispenser or by dipping the end portion of a
standard capillary tube into the liquid sample container to pick up a droplet
. If a
standard capillary tube is used, the capillary tube does not have a tapered
construction at one end but preferably has substantially the same width along
its
entire length. For example, a tubular shaped capillary member is suitable for
use.
It will be appreciated that structure other than a capillary tube can be used
so long as
it contains an electrically charged end that is shaped and sized to permit the
formation of a liquid sample droplet thereat.
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A droplet of liquid sample, preferably less than 200 nl, is initially
held at the flat, open end of the said capillary tube within the microfluidic
channel
of the nozzle device and extends beyond this end. The relative surface
tensions and
other characteristics of the liquid sample and the hydrophobic nature of the
polymeric microfluidic channel, favor the formation of a small droplet (liquid
tip)
at the end of the capillary tube. The outer surface of the capillary tube has
a
conductive layer formed thereon at least at the end section where the droplet
is
formed. After inserting the capillary tube through the reservoir section, into
the
channel and then into the nozzle such that the droplet is contained within the
nozzle,
an electric field is generated at this end by coupling the conductive layer of
the
capillary tube to a high voltage source and then activating the voltage source
to form
the electric field. When high voltage is applied to the capillary tube, the
droplet
(liquid sample) lengthens to form a conical shape, the tip of which evaporates
to
form ions of the sample molecules and extremely fine nanoscale or picoscale
droplets carrying charges. As opposed to the vapor plume that is created in
traditional nanospray applications, the present invention does not have a
liquid spray
component that is nearly as defined as in the traditional nanospray
applications.
Instead, the discharge is comprised of ions and extremely small droplets
(e.g., of
nanoscale or smaller dimensions) carrying charges. Advantageously, this
eliminates
or substantially reduces the -need for a drying mechanism to dry the liquid
droplets
to release the ions. In the case of traditional nanospray applications, a
desolvation
gas is very often needed to dry the droplets by flowing a dry nitrogen gas
into the
vapor plume. Thus, the present method provides a less complex system that
reduces
the time and cost associated with pumping sample through the capillary and
also
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drying the liquid droplets, and consumes an extremely small quantity of the
sample
material. The detailed mechanism of this ion-producing method is not known for
certain. Another possibility is corona discharge occurring at the electrode
within the
partially-filled microfluidic channel.
One other difference between the present techniques using the
polymeric nozzle device, whether pumped or not pumped, and the conventional
nanospray technique is that the electric field for vaporizing and ionizing the
liquid
sample is formed by the liquid tip (the liquid sample droplet) due to its
shape and
location instead of the actual tapered structure of the capillary tube. The
liquid tip
formation is helped by the material property of the microfluidic channel
containing
the droplet which is preferably a material not wetted by the liquid aqueous
sample.
Polymeric materials or a material covered by a polymeric layer are suitable
materials. Materials with good thermal conductivity are also suitable, as well
as
polymeric materials with impregnated electrical and thermally conducting
additives
such as carbon and metallic particles. In the present processes disclosed
hereinbefore, the diameter of the polymer nozzle opening affects the voltage
needed
to create a spray of a given liquid. For a nozzle opening of 20-30 microns in
diameter, the applied voltage can be between ~ 2 to 2.5 KV to create a fine
spray
of 40 % methanol/60 % water. When spraying with an approximately 50 micron
diameter, the applied voltage can be higher to about ~ 3 to 3 .5 KV . Once the
spray
has initiated, it is possible to lower the voltage to approximately 1.3 KV to
maintain
the spray. The outside diameter of the nozzle can vary between 50 to 150
microns.
The outside diameter of the polymer nozzle can be larger than 150 microns.
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The reference electrode, or counter electrode, can be placed from 0.5
mm to several mm from the nozzle opening. The closer the counter electrode is
to
the nozzle opening, the lower the applied voltage has to be for the liquid to
start
spraying. The difference in the required voltage can be in the range of a few
hundred volts for when the counter electrode is approximately 0.5 mm away and
over 1 mm away from the nozzle opening.
The advantages of the present process are the following: (1) nozzles
of a variety of inside diameters can be fabricated to adapt to a range of flow
rate
requirements and contents of the liquid samples without affecting the applied
voltage
greatly; (2) micro-injection molding technology for polymers produces
sufficiently
fine structures in nozzles fabricated from a variety of polymer materials and
further
injection molding is a low-cost manufacturing technology; and (3) nozzles with
a
relatively large outside diameter can be used to create fine plumes comparable
in
properties as those created by the smaller nozzles, wherein the larger outside
diameter minimizes the possibility of physical damage to the nozzles.
The inside diameter of the nozzles can be made large enough to spray
droplets of viscous liquid, such as polymer solutions, for application in
array
spotting and nano particle fabrication of polymers. Organic dyes used in
organic
LED display, regular dyes used in conventional ink jet printing and other
materials
that require fine droplets or nanoscale droplets may be sprayed with these
array
devices to achieve high resolution of the droplets as well as high speed. The
present design constructions thus overcome the above noted disadvantages that
were
associated with the prior art.
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Turning now to Figs. 34-35, as previously mentioned, spraying a
liquid through a constricted opening with the aid of an electric field is a
widespread
process for generating a vapor plume for a variety of applications. In the
application for mass spectrometry, the vapor plume carrying the ions of the
molecules of interest is directed into the mass spectrometer where the masses
of the
ions of the molecules are obtained. From the mass of the molecule, the
chemical
nature of each molecule is identified.
The polymeric nozzle array devices described hereinbefore (e.g.,
device 100) each has a relatively high surface area in close proximity to the
spray
containing numerous ionic species. These charged species can strike the
polymer
surface of the nozzle array device and create static electric fields that
change in an
unpredictable manner as more and more charged species hit the polymer surface
during the spray. If the charges are not drained away from the insulating
polymer
surface by some means, the stray field accumulate on the insulating surface
and this
will prevent the ions in the spray from getting into the inlet cone 1030 of
the mass
spectrometer 1000. When the stray field build-up is large enough, it subtracts
the
electric field felt by the droplet at the nozzle tip and stops the spraying
altogether.
There are a number of different techniques or means that can be used
to prevent or control the build-up of the electric field on the polymeric
nozzle array
device. The following are several exemplary means for preventing or
controlling
the build-up of the electric field on the polymeric nozzle array surface. It
will be
understood that one or more of the following methods for discharging the stray
electric field build-up can be incorporated into the nozzle array device.
First, the
surface of the polymeric nozzle array device can be coated with a layer of
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conducting material of high resistivity, for example, about 1 gigaohm. The
material
can be a thin layer of noble metal coating, or a layer of salt coating. Salts
that are
suitable for use can be chosen from sodium iodide, rubidium iodide, silver
halides,
barium sulfate and the like. Second, a capacitor of an appropriate value can
be
electrically connected between the polymeric nozzle array device surface and
electrical ground. The capacitor is charged up by the electrical charges from
the
stray ions and electrons and discharges the electrical charges to electrical
ground at
controlled intervals. Third, a salt solution containing sodium iodide and
rubidium
iodide or other salts can be added to the sample liquid for spraying so that a
layer of
salt coats the device surface during the spray to drain the stray charges
away.
Fourth, an anti-static additive can be added to the polymer resin during the
injection
molding process so that the resultant polymeric nozzle device can have an anti-
static
property. The additive can be a highly conjugated polymer, such as polyaniline
or
the like. Likewise a premixed commercially available anti-static polymer resin
as
one supplied by HiTech (Hebron, Kentucky) may be used for injection-molding
polymeric nozzle array devices with an appropriate anti-static property. A
preferred
anti-static polypropylene is especially suitable.
Fifth and as illustrated in Figs. 34-35, a conducting shield 1900 made
of a sheet of metal or an insulator with a metallic coating can be placed
between the
nozzle tip and the mass spectrometer inlet (e.g., inlet cone 1030 of Fig. 23)
to act as
a physical barrier for catching the sprayed droplets that can otherwise be
falling on
the surface of the nozzle array device 100. The shield 1900 should have an
aperture
1910 and be placed about 1 mm from the nozzle tip and the aperture 1910 should
be
large enough for the beginning part of the spray to come through. Figs. 34-35
show
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one exemplary placement of the shield 1900. In this configuration, the shield
1900
is held at a distance defined by the height of the posts 1160 on the frame
1100 of the
device 100. While the distance between the shield 1900 and the nozzle tip will
vary
depending on the length of the posts 1160, it is preferred that this distance
be less
than 1 mm. In other words, the shield 1900 can be attached to the posts 1160
and
extend across the device 100 with each nozzle 150 having an associated
aperture
1910 formed in the shield 1900. While, the dimensions of the shield 1900 can
vary,
in one exemplary construction, the shield 1900 has a thickness from about
0.005
inch to 0.010 inch.
There are a number of different ways to attach the shield 1900 to the
posts 1160. For example, an adhesive or bonding material can be applied to the
posts 1160 and/or select locations of the shield 1900. In addition, the shield
1900
can include a number of hubs that equal the number of posts 1160 and each
posts
1160 mates with the hub so as to removably couple the shield 1900 to the posts
1160
and thereby couple the shield 1900 to the frame 1100 and the microfluidic
nozzle
array device 100. In one exemplary embodiment, each hub is in the form of a
hollow protrusion (e.g., tube-like structure) that extends outwardly from an
inner
surface of the shield 1900 that faces the frame 1100. The shield 1900 is
removably
coupled to the frame 1100 by inserting the posts 1160 into the hollow interior
of the
hubs so that the two parts are securely coupled to one another. If it is
desired to
remove the shield 1900, the shield 1900 can simply be pulled away from the
posts
1160. By having a shield that is removable from the microfluidic device 100
and
the holder 1120, interchangeability of the individual components is permitted.
For
example, the construction of the shield 1900 depends on the construction of
the
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device 100 and more specifically, it depends on the number and arrangement of
the
nozzles 150 since there needs to be one aperture 1910 for one nozzle 150.
Thus, if
the device 100 has a first array arrangement, a first shield 1900 is required
and if
the device 100 has a second array arrangement that is different from the first
arrangement, a second shield 1900 is likely required. Further, because the
shield
1900 is not rigidly connected to or made integral with the holder 1120, the
holder
1120 can be used with a number of different types of shields 1900 and
microfluidic
devices 100.
In an alternative embodiment, the shield 1900 is removably coupled
to the holder 1120 using mechanical fasteners. For example, the shield 1900
can
have securing tabs extending outwardly therefrom the receive fasteners that
are
securely attached to the holder 1120 itself, thereby resulting in the shield
1900 being
securely yet removably attached to the holder 1120. In other words, fasteners,
such
as screws or the like, are used to removably attach the shield to the holder
1120. In
this embodiment, the shield 1900 is preferably positioned so that the inner
surface of
the shield 1900 seats against the posts 1160 after the shield 1900 is securely
fastened
to the holder 1120. This is desirable because the posts 1160 can then be used
to
space the shield 1900 the proper distance from the nozzle tips. Thus,
regardless of
the actual construction of the shield 1900, it will be uniformly placed a
prescribed
distance from the nozzle tips by making sure that the shield 1900 seats
against the
posts 1160 when it is fastened to the holder 1120. In this embodiment, the
shield
1900 can either be placed above the rail 1140 or on the planar platform 1130.
The
shield 1900 can also be made as an integral part of posts 1160 in that a
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process can be used to form the frame 1100, posts 1160 and the shield 1900
integrally attached thereto.
In yet another embodiment, the rail 1140 can be constructed so that it
includes a longitudinal groove extending therein. The longitudinal groove is
sized
so that the shield 1900 is received therein in a snug manner so as to securely
couple
the shield 1900 to the holder 1120. In other words, the frictional fit between
the
shield 1900 and the rail 1140 securely holds the shield 1900 in a vertical
position
parallel to the microfluidic device 100. Once again, the shield 1900
preferably seats
against the posts 1160 for the above reasons when the shiel 1900 is securely
held in
the groove of the rail 1140. In this embodiment, the shield 1900 is removable
since
it can easily be pulled out of the groove formed in the rail 1140.
Sixth and as illustrated in Fig. 36, the nozzle array device 100 can
have the amount of plastic perpendicular to the spray direction reduced by
placing
through holes 1930 in the surface of the array device 100. In this embodiment,
the
body of the nozzle cone (nozzle 150) can also be made longer so that the
distance
between the nozzle tip and the flat surface of the nozzle array device 100
perpendicular to the spray direction is maximized.
It will be appreciated that the aforementioned means to prevent or
control the build-up of the electric field on the polymeric nozzle array
surface can
be used in combination with any of the microfluidic nozzle array devices
disclosed
herein.
While the invention has been particularly shown and described shown
and described with reference to preferred embodiments thereof, it will be
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understood by those skilled in the art that various changes in form and
details may
be made therein without departing from the spirit and scope of the invention.
