Note: Descriptions are shown in the official language in which they were submitted.
CA 02451201 2003-12-19
WO 03/000422 PCT/US02/19924
Microfabricated Two-Pin Liquid Sample Dispensing System
Reference to Related Applications
The present application claims priority to U.S. Provisional Patent Application
Serial No. 60/299,515 filed June 20, 2001, U.S. Provisional Patent Application
Serial
No. 60/325,001 filed September 25, 2001, U.S. Patent Application 10/027,171
filed
December 21, 2001, U.S. Patent Application 10/028,852 filed December 21, 2001,
U.S.
Patent Application 10/027,484 filed December 21, 2001, U.S. Patent Application
10/027,516 filed December 21, 2001, U.S. latent Application 10/027,922 filed
December 21, 2001, and U.S. Patent Application 10/029,108 filed December 21,
2001,
all of which are expressly incorporated by reference.
Field of the Invention
The present invention relates to a liquid dispensing system for forming and
dispensing droplets of a liquid sample.
Background of the Invention
Many chemical, biomedical, bioscience and pharmaceutical industries require
chemical operations, such as reactions, separations and subsequent detection
steps, to be
performed on samples. It is generally desirable to introduce these samples
into a sample
handling system, such as a microfluidic system capable of handling and
analyzing
chemical and biological specimens, quickly, efficiently and in a highly
controllable
manner.
Many methods have been described for the interfacing of fluids, e.g., samples,
analytes, reagents, precursors for synthesis and buffers, towards, within or
between
microfluidic systems. Generally, introduction of a liquid sample to a
microfluidic
system is accomplished through sample channels or sample wells. To introduce a
liquid
sample to the microfluidic system, a capillary tube may be provided, which
dispenses a
liquid sample to a sample well, sample channel or other sample introduction
port. A
significant drawback of using a capillary tube concerns the low injection
efficiency
inherent to capillary tubes, that is, the ratio between the volume of liquid
required for a
particular chemical operation in a part of the microfluidic system, and the
total volume
of liquid required for the introductory operation. Moreover, it is generally
difficult to
control the precise volume of dispensed sample using capillary tubes.
Furthermore,
capillary tubes are subject to contamination, because the same port used to
fill the tube is
also used to eject the liquid sample.
-1-
CA 02451201 2003-12-19
WO 03/000422 PCT/US02/19924
U.S. Patent Number 6,101,946 of Martinsky, the contents of which axe herein
incorporated by reference, describes a pin-based system for printing
microarrays of
biochemical substances. The microaxray printing system comprises a stainless
steel
printing pin having a sample channel and a flat tip that is machined with an
electronic
discharge machine (EDM). The pin applies a biochemical substance by filling
the
sample channel and subsequently directly contacting a printing substrate, to
deliver the
sample from the sample channel to the printing substrate. A drawback of the
pin-based
system described in the '946 patent concerns the ability to control the amount
of
delivered sample. The pin-based system is subject to contamination and
breakage,
because it requires direct contact between the pin tip and the printing
substrate. Another
drawback concerns the difficulty of precisely positioning the tip of the pin
to provide
sufficient contact to result in delivery of a sample.
U.S. Patent Number 6,110,426 of Shalon et al., the contents of which are
herein
incorporated by reference, describes a capillary dispenser for forming
microarrays of
biological samples. The capillary dispenser comprises an elongate open
capillary
channel adapted to hold a liquid sample. The channel is formed by a pair of
spaced-
apart, coextensive, elongate members, which are tapered toward one another and
converge at a tip region at the lower end of the channel. The elongate members
are
fixed relative to each other and the capillary channel is limited to a fixed
volume.
Furthermore, it is difficult to control the amount of sample that is acquired
and
dispensed from the capillary dispenser of the '246 patent.
Summary of the Invention
The present invention provides a sample dispensing system comprising two
microfabricated interacting pins for forming and dispensing droplets of a
liquid sample.
Each pin includes a tip spaced predetermined distance from the other pin to
define a
sample acquisition region. The pins acquire and hold a droplet of the liquid
sample in
the sample acquisition region formed in the space between the tips and apply
the droplet
to a selected sample handing system. The distance between the tips is variable
to
accommodate different liquid samples having varying physical properties and to
vary the
volume of the acquired droplet.
According to a first aspect, a droplet dispensing system is provided. The
droplet
dispensing system comprises two separately movable pins for holding a droplet
of a
liquid sample. The droplet dispensing system comprises a holder, a first pin
connected
-2-
CA 02451201 2003-12-19
WO 03/000422 PCT/US02/19924
to the holder and having a first tip and a second pin connected to the holder
and having a
second tip spaced an initial separation distance from the first tip to form a
sample
acquisition region for holding a predetermined volume of liquid sample. The
initial
separation distance is variable.
According to a second aspect, a method of applying a droplet of liquid sample
to
a substrate is provided. The method comprises providing a dispensing system
comprising two pins separated by a variable distance, immersing the pin tips
in a
reservoir to acquire a droplet of a liquid sample, and contacting the
substrate to deposit a
spot of the liquid sample on the substrate. The spot has a predetermined
volume less
than the volume of the droplet.
According to another aspect, a method of diluting a first liquid sample in a
second liquid is provided. The method comprises providing a dispensing system
comprising two pins having a first tip and a second tip separated from the
first tip by a
variable distance, acquiring a droplet of the first liquid sample between the
pins and
immersing the pin tips containing the droplet of the first liquid sample in a
second
reservoir containing a second liquid, whereby the droplet of the first liquid
sample is
diffused into the second liquid.
According to another aspect, a two-pin droplet dispensing system is provided.
The two-pin droplet dispensing system comprises a holder, a first pin
connected to the
holder and having a first tip and a second pin connected to the holder and
having a
movable tip spaced a predetermined distance from the first tip to form a
sample
acquisition region for holding a predetermined volume of liquid sample. The
system
further comprises a driver for effecting movement of the movable tip with
respect to the
first tip.
According to a final aspect, a liquid sample dispensing system comprising a
holder a first pin having a first tip and a relaxation region for absorbing an
impact on the
tip is provided.
Brief Description of the Figures
Figures la and 1b illustrate the two-pin dispensing system of an illustrative
embodiment in a sample acquisition mode.
Figure 2 illustrates the two-pin dispensing system of an illustrative
embodiment
in a spotting mode.
-3-
CA 02451201 2003-12-19
WO 03/000422 PCT/US02/19924
Figures 3a and 3b illustrate the two-pin dispensing system of an illustrative
embodiment in a dilution mode.
Figure 4 illustrates an alternative embodiment of the two-pin dispensing
system,
including a fixed pin and a movable pin.
Figure 5 is a detailed view of the fulcrum region of the two-pin dispensing
system of Figure 4.
Figure 6 is a detailed view of the driver of the two-pin dispensing system of
Figure 4.
Figures 7a, 7b and 7c are detailed views of the tip region of the two pins of
the
pin dispensing system of Figure 4.
Figure 8 illustrates the relaxation region of the pin dispensing system of
Figure 4.
Figure 9 is a scanning electron microscope (SEM) image of an array of two-pin
dispensing systems that are microfabricated from a silicon wafer according to
the
teachings of the illustrative embodiment of the present invention.
Figure 10 is a SEM image showing a detailed view of a tip region of one of the
two-pin dispensing systems of Figure 9.
Figure 11 is a SEM image illustrating an array of two-pin dispensing systems
having relaxation regions that are microfabricated from a silicon wafer
according to the
teachings of the illustrative embodiment of the present invention.
Detailed Description of the Illustrative Embodiments
The present invention provides a dispensing system for dispensing a
predetermined volume of liquid sample. The dispensing system of the present
invention
provides precise acquisition and delivery of a liquid sample to a sample
handling system
using two interacting pins. The dispensing system is suitable for use in a
basic research
or a commercial environment. The dispensing system significantly improves
sample
introduction into a sample handling system by increasing the efficiency, speed
and
controllability of forming and dispensing droplets while significantly
reducing waste and
contamination. The invention will be described below relative to an
illustrative
embodiment. Those skilled in the art will appreciate that the present
invention may be
implemented in a number of different applications and embodiments and is not
specifically limited in its application to the particular embodiment depicted
herein.
Figures la and 1b illustrate a two-pin dispensing system 10 of an illustrative
embodiment of the present invention in a sample acquisition mode for acquiring
a
droplet of a liquid sample having a predetermined volume from a reservoir
containing a
supply of the liquid sample. The illustrative two-pin dispensing system 10
comprises a
pair of separately movable, interacting pins sized and configured to hold a
droplet of
-4-
CA 02451201 2003-12-19
WO 03/000422 PCT/US02/19924
liquid between the tips of the pins. The two-pin dispensing system 10
comprises a first
pin 11 and a second pin 12, which are movably connected to a holder 13. The
tips 11 a,
12a are separated by an initial separation distance D to form a sample
acquisition region
14 in the space between the tips. The position of each pin is controlled using
actuators
15 located in one or more of the pins 1 l, 12. According to an alternate
embodiment,
sensors 16 are provided on one or more of the pins 11, 12 to measure the
separation
distance D between the pin tips l la, 12a. Those of ordinary skill in the art
will readily
recognize that the holder of the invention can include any suitable structure
for retaining
or holding the pins.
To acquire a droplet of a liquid sample, such as a biological sample, the pin
tips
11 a, 12a are immersed in a reservoir 17 containing a supply of a selected
liquid sample.
The pin tips 11 a, 12a are positioned to allow capillary flow into to sample
acquisition
region 14. The capillary force induced in the sample acquisition region 14
pulls a
droplet 18, having a volume defined by the separation distance of the pin tips
11 a, 11 b,
into the sample acquisition region 14. The capillary force produced between
the
surfaces of the pin tips holds the droplet in the sample acquisition region 14
formed
between the two pin tips l la, 1 1b. The actuators 15 in the pins 1 l, 12 move
the pins to
vary the separation distance D between the tips, thereby varying the amount of
sample
that is acquired by the two-pin dispensing system, or to dispense the sample
therefrom.
According to the illustrative embodiment, the two-pin dispensing system 10 is
configured to acquire liquid samples in volumes between about fifty picoliters
and about
fifty nanoliters. One skilled in the art will recognize that the acquired
volume is not
limited to this range and that the pins may be spaced apart to accommodate any
suitable
volume of liquid.
The actuators 15 can also compensate for varying physical properties of the
particular liquid sample, such as viscosity, surface tension, and the like, by
modifying
the separation distance D between the pins. The sensors 16 may also be
utilized to
measure the force applied between the tips and the physical properties of the
acquired
liquid sample on the fly. In this manner, the settings (i.e. the pin
separation distance) of
the pin dispensing system 10 can be modified to compensate for variations in
the
measured properties of the liquid sample in real time.
According to the illustrative embodiment, the droplet dispensing system 10 is
fabricated from a silicon wafer using a microfabrication technique, such as a
standard
photolithography etching process, to fabricate the pin structures. One skilled
in the art
-5-
CA 02451201 2003-12-19
WO 03/000422 PCT/US02/19924
will recognize that alternative materials and manufacturing techniques may be
utilized.
For example, the pin dispensing system may be made out of glass, plastic or
any other
suitable material. According to one embodiment, an array of droplet dispensing
systems
10, each comprising two pins having a variable separation distance, may be
formed on a
single substrate, such as a silicon wafer. For example, an array of up to
about 300 or
more two-pin dispensing systems 10 may be formed on a four-inch silicon wafer.
Figure 2 illustrates the two-pin dispensing system 10 of the illustrative
embodiment in a spotting mode. The two-pin dispensing system 10 may be
utilized as a
spotting system for printing or discharging arrays of biochemicals, such as
nucleic acid
molecules or proteins, or other suitable liquid samples to a sample handing
system, such
as a printing substrate, titre plate, microfluidic system or device, and the
like for use in
proteomics, genomics, screening, diagnostics and other applications. After the
dispensing system acquires a droplet, the dispensing system is moved in close
proximity
to a surface 20. The surface 20 may comprise a solid surface or a liquid. The
surface 20
may comprise a porous structure, such as a porous membrane, or a non-porous
structure,
such as a microscope slide. The loaded pins deposit a spot 21 on the surface
20 having a
selected spot volume by direct contact between the pin tips l la, l 1b and the
surface.
The separation distance D2 during contact may be varied to increase or
decrease the
volume of the dispensed spot of the liquid sample. According to the
illustrative
embodiment, the volume of the dispensed spot 21 is significantly smaller than
the
volume of the acquired droplet 18, and is generally sub-nanoliter in volume,
though one
skilled in the art will recognize that the invention is not limited to this
range.
The use of the two-pin dispensing system of the illustrative embodiment in
spotting applications provided enhanced control over the size of the deposited
spots in a
microarray, and also allows for smaller spots to be formed and deposited.
The pin dispensing system may further be utilized as a wet deposit system with
dilution to dilute a selected volume of a first liquid in a second liquid
sample. Figures
3a and 3b illustrate the two-pin dispensing system 10 in a dilution mode,
wherein the
acquired droplet 18 of a sample is diluted in a larger supply of a target
fluid 30. After
the dispensing system 10 acquires a droplet 18, the size of which is defined
by the
separation distance of the pin tips 11 a, 12a, the pin tips 11 a, 12a are
immersed in a
reservoir 30 containing a target fluid. The droplet 18 automatically dilutes
into the
target fluid via mixing and diffusion. To accelerate the dilution process, the
separation
distance of the tips 11 a, 12a may be increased during dilution using the
actuators 15.
-6-
CA 02451201 2003-12-19
WO 03/000422 PCT/US02/19924
Figure 4 illustrates a two-pin dispensing system 40 having a fixed pin and a
movable pin according to an alternate embodiment of the invention. In the two-
pin
dispensing system of Figure 4, the resting position of a first pin 41 is fixed
relative to a
substrate 43 and the resting position of the second pin 42 is movable relative
to the first
pin 41 and the substrate 43. The two-pin dispensing system 40 further includes
a driver
44 for varying the separation distance between the tips 41a, 42a by adjusting
the position
of the second movable pin 42 in a fulcrum region 46. According to the
illustrative
embodiment, the movable pin rotates about a fixed pivot point 45 under the
control of
the driver 44 to adjust the separation distance at the tips. According to the
illustrative
embodiment, the pins 41, 42 further include a relaxation region 51 for
preventing
breakage of the tips. One skilled in the art will recognize that the
relaxation region 51
may be formed in one or both of the pins 41, 42 of the two-pin dispensing
system 40.
The illustrative two-pin dispensing system 40 is formed from a silicon wafer
using a standard photolithography etching process to fabricate the pins 41,
42, the
relaxation region 51, the driver 44, and the fixed point 45 of the fulcrum
region 46 in the
wafer substrate 43. According to the illustrative embodiment, the two-pin
dispensing
system 40 is fabricated from a silicon wafer having dimensions of about one
square
centimeter. The pins 41,42 have a length of about five millimeters, though one
skilled in
the art will recognize that the invention is not limited to this size.
According to an
alternate embodiment, a larger silicon wafer or other suitable substrate is
provided, and
an array of pin dispensing systems is fabricated on the larger silicon wafer.
For
example, a silicon wafer having a size of about ten square centimeters may be
used to
fabricate an array of about seventy two-pin dispensing systems 40 thereon. A
fifteen
square centimeter silicon wafer can be utilized to fabricate over one hundred
two-pin
dispensing systems 40 in the silicon wafer substrate. Those of ordinary skill
will readily
recognize that any suitable configuration can be employed to move one or both
of the
pins.
Figure 5 is a detailed view of the fulcrum region 46 of the two-pin dispensing
system of Figure 4. The movable pin 42 is configured to pivot about a fixed
point 45 to
vary the separation distance of the two pin tips. The driver 44 applies a
force to an
application region 47 of the fulcrum region 46 to cause the movable pin 42 to
rotate,
thereby effecting movement of the movable pin tip 42a relative to the tip 41 a
of the
fixed pin 41. As illustrated, the fulcrum region 46 includes gaps 48 are
formed in the
substrate 43 adjacent to the fixed point 45 to allow for rotation of the pin
42 about the
fixed point in response to activation of the driver 44.
CA 02451201 2003-12-19
WO 03/000422 PCT/US02/19924
According to an alternate embodiment of the invention, the fulcrum region
further includes bending sensors, illustrated as piezoresistors 62, on the
left and right
side of the fulcrum region to allow differential sensing of actual bending of
the pin 42 in
the fulcrum region. In this manner, the amount of bending, and the resultant
tip
separation distance may be controlled using a closed loop feedback system. The
use of
bending sensors further limits nonlinear temperature effects by allowing real-
time
sensing of tip displacement.
Figure 6 is a detailed view of the driver 44 of the two-pin dispensing system
40
of Figure 4. As shown the driver 44 comprises a bar of silicon that imparts a
force on
the application region 47 of the fulcrum 46 to move of tip 42a a predetermined
amount.
According to the illustrative embodiment, the driver 44 expands a
predetermined amount
in response to a temperature increase. The expansion of the driver 44 forces
rotation of
the fulcrum about the pivot point. According to the illustrative embodiment,
the system
is configured such that the ratio between the amount of movement of the tip
42a in
response to expansion of the driver 44 to the amount of expansion of the
driver is greater
than one hundred. In other words, a driver expansion of one micron causes a
one
hundred micron displacement of the pin tip 42a.
According to the illustrative embodiment, the driver 44 has an initial length
L of
four millimeters. A thirty-degree rise in temperature of the silicon results
in a 1.08
micrometer expansion of the driver 44. The expansion of the driver 44 forces
the pin 42
to rotate about the fixed pivot point 45, thereby increasing the separation
distance
between the tips 41a, 42a by greater than 108 microns.
According to the illustrative embodiment, heating resistors 49 are affixed to
the
driver for applying heat to the driver 44. The heating resistors may comprise
poly
resistors, diffused resistors or any suitable means for applying heat to the
driver 44 in
order to effect controlled expansion of the driver 44 and to vary the
separation distance
between the tips 41 a, 42a. Optionally, cooling fins (not shown) are provided
in the
driver 44 near the fulcrum region 45 to prevent unwanted heating of the driver
in the
fulcrum region. According to an alternate embodiment, a temperature sensor
(not
shown) in communication with the heating means is included in the two-pin
dispensing
system 40 to provide closed loop control of the driver 44 temperature.
One skilled in the art will recognize that the two-pin dispensing system is
not
limited to the illustrative driver. According to alternate embodiments the
driver 44
comprises an electrostatic system, a piezoelectric system, an
electromechanical system, a
_g_
CA 02451201 2003-12-19
WO 03/000422 PCT/US02/19924
thermoelectric actuator or any suitable system for applying a predetermined
and defined
force to cause controlled adjustment of the separation distance between the
pin tips 41 a,
42a. One skilled in the art will further recognize that the two-pin dispensing
system is
not limited to a fulcrum for varying the separation distance and that any
suitable
mechanism for varying the separation distance may be utilized.
Figures 7a and 7b are detailed views of the tip region of the two pins of the
two-
pin dispensing system 40 of Figure 4. As discussed, the tips 41 a, 42a are
spaced apart a
predetermined distance D, which is defined by the driver 44. Each tip includes
a sample
contact surface 70, defined by the tip height H and the tip depth S, which are
fixed
values determined by the shape of the sample surfaces 70. The volume of the
sample
acquisition region 14 and thus the volume of an acquired sample droplet
corresponds to
the volume of the space defined between the tips, or the product of the tip
height H, the
tip depth S and the separation distance D. For example, according to the
illustrative
embodiment, the separation distance D between the pin tips 41 a, 42a is
between about
twenty-five microns and about one hundred twenty five microns. For tips having
a tip
depth of about fifty microns and a height of about two hundred microns, the
resulting
volume of a captured droplet is between about 250 picoliters and about 1.25
nanoliters.
For tips having a tip depth of 100 microns and a height of about 400 microns,
a tip
separation distance between about 25 and 125 microns results in an acquired
droplet
having a volume of between about 1.0 nanoliters and about 5 nanoliters. Tips
having a
depth of 500 microns and a height of 500 microns, form a droplet having a
volume
between about 6.25 nanoliters and about 31.5 nanoliters when the separation
distance
between the tips is between about 25 and about 125 microns.
The tip contact surfaces 70 defined by the tip heights H and tip depths S may
form parallel faces or, according to a preferred embodiment, may be tapered,
so that the
separation distance D is reduced towards the bottom and/or front of the tip
surface. In
this manner, smaller droplet volumes may be accommodated. The slope of the
tips 41 a,
42a may be varied in regions 71 and 72 to improve droplet shape and enhance
delivery
of the droplet.
Figure 7c is a cross-sectional view of the tips 41a, 42a according to an
alternate
embodiment. According to the alternate embodiment, the tip surfaces 70' are
curved to
hold form a cylindrical or conical sample acquisition region 14 therebetween.
-9-
CA 02451201 2003-12-19
WO 03/000422 PCT/US02/19924
According to alternate embodiment, the one or both of the tip surfaces 70
and/or
the outside shaft surface are coated with a hydrophilic, hydrophobic or other
chemical
coating to enhance droplet acquisition and dispensing. For example, the tips
41, 42 may
be formed of or coated with a hydrophilic coating to enhance retention of a
sample in the
sample acquisition region. According to one embodiment, the outside shaft
surfaces of
the tips 41,42 are coated with gold or another suitable hydrophobic material
without
affecting the tip surfaces 70 defining the sample acquisition region 14. The
use of a
metal coating provides enhanced control over the volume and release of a
droplet. The
use of silicon and/or gold additionally allows for more vigorous cleaning
solutions to be
utilized when cleaning the tips without degrading the system. In this manner,
contamination of the tips is reduced.
The coating may be applied in a pattern to the tip surfaces 70 or the other
surfaces of the tips 41, 42 by shadow masking. The coating may be sputtered,
or
evaporated on a surface in a predetermined pattern, defined by a mask. One
skilled in
the art will recognize that any suitable pattern for directing the liquid
sample and
enhancing control over sample acquisition and dispensing may be utilized.
According to another embodiment, the dispensing system may comprise a single
pin having a suitable pattern coating applied to the surfaces of the pin tip.
For example,
the shaft of the single pin may be coated with a suitable hydrophobic coating
and the tip
of the pin may be coated with a suitable hydrophilic coating to enhance
acquisition and
dispensing of a liquid sample.
Figure 8 illustrates the relaxation region 51 of the pin dispensing system 40
of
Figure 4. The pin tips 41, 42 are brittle and subject to breakage when
accidentally
touched down to surfaces, due to their size and the material used to fabricate
the pins.
The illustrative relaxation region 51 comprises a spring 52 formed between the
tip 41 a
and the substrate 43. When the tip 41 a contacts a surface, the spring absorbs
the impulse
and retracts the tip 41 a to prevent breakage. The springs 52 in the pins are
configured to
move the corresponding tip up and away from the other tip to prevent collision
of the
tips. The invention is not limited to the illustrative spring design. One
skilled in the art
will recognize that any suitable spring design may be utilized to form the
relaxation
region 51 to protect the pin tips from breakage.
According to an alternate embodiment, the spring 52 includes sensors to
measure
of the force of contact between the tip and a surface. For example,
differential
piezoresistive sensors may be included in the spring 52 and connected to an
actuator (not
- lo-
CA 02451201 2003-12-19
WO 03/000422 PCT/US02/19924
shown) to control the spring using feedback control loop. The spring sensor
may also be
utilized to measure the force exerted by the droplet on the tips, and allow
the driver to
compensate for variable forces exerted by the droplet on the tips.
According to an alternate embodiment of the present invention, a relaxation
region may be implemented in a two-pin dispensing system comprising a pair of
spaced-
apart, fixed pins defining a sample acquisition region of fixed volume.
As discussed, the two-pin dispensing system 10 or 40 of the illustrative
embodiment may be microfabricated from a suitable substrate, such as silicon,
glass or
plastic. According to the illustrative embodiment, photolithography may be
utilized to
form the pin structures in the substrate. In photolithography, the pattern of
the two pins
and other components of the two-pin dispensing system 10 or 40 are imprinted
on a
silicon wafer, or other substrate, using one or more photoresist layers that
are patterned
by UV or other light projected through one or more photo-masks containing the
pattern
on it. The substrate is then etched to fabricate the two-pin structure. One
skilled in the
art will recognize that any suitable microfabrication technique may be
utilized to
manufacture the two-pin dispensing system of the illustrative embodiment of
the present
invention.
One skilled in the art will recognize that the described microfabrication
technique may further be utilized to fabricate single-pin dispensing systems
from a
silicon wafer or other suitable substrate. For example, it is within the scope
of the
invention to microfabricate a single-pin structure having two tips forming a
sample
channel for acquiring and dispensing a liquid sample, as described in U.S.
Patent
Number 6,101,946, from a silicon wafer by etching the silicon wafer to define
the pin
and sample channel.
Figure 9 is a scanning electron microscope (SEM) image of an array of two-pin
sample dispensing systems 100 according to an embodiment of the invention and
formed
from a silicon wafer 101 using the above-described microfabrication technique.
As
shown, a plurality of two-pin dispensing systems are fabricated from a single
silicon
wafer substrate. Each two-pin dispensing system comprises a pair of elongated
pins that
are spaced apart to define a sample acquisition region between the tips of the
pins.
Figure 10 is another SEM image showing a detailed view of the tip region of
one of the microfabricated two-pin dispensing systems of Figure 9. As shown,
the pins
axe etched in a silicon wafer to define a sample acquisition region 140
between the tips
-11-
CA 02451201 2003-12-19
WO 03/000422 PCT/US02/19924
of the pins. As illustrated, the microfabricated pin tips have a separation
distance of less
than about 100 microns.
Figure 11 is another SEM image of an array of microfabricated two-pin sample
dispensing systems 110 having relaxation regions 51 according to an embodiment
of the
invention. As shown, the array is also formed from a silicon wafer 101 using
the above-
described microfabrication technique. The relaxation region 51 is formed by
etching the
silicon wafer in the region between the pin tips and the holder to define a
spring for
absorbing an impact on the tips. The relaxation region 51 prevents breakage of
the pin
tips 41, 42 when the pin tips contact a surface.
The two-pin dispensing system provides significant improvements to the process
of forming and dispensing droplets of samples for spotting and dilution
applications.
The illustrative configuration provides precise control over the amount of
liquid sample
that is acquired and deposited through the use of two pins having a variable
separation
distance. Adjusting the separation distance between the pin tips easily and
precisely
modifies the volume of the acquired liquid droplet and the deposited liquid
droplet.
Furthermore, measurements of the physical properties of the liquid volume can
be made
on the fly and the tip separation can be modified quickly and easily to
compensate for
variations. The use of sensors provides precise control of the tip separation
distance to
optimize the process of acquiring and dispensing droplets of a liquid sample.
The present invention has been described relative to an illustrative
embodiment.
Since certain changes may be made in the above constructions without departing
from
the scope of the invention, it is intended that all matter contained in the
above
description or shown in the accompanying drawings be interpreted as
illustrative and not
in a limiting sense.
It is also to be understood that the following claims are to cover all generic
and
specific features of the invention described herein, and all statements of the
scope of the
invention which, as a matter of language, might be said to fall therebetween.
Having described the invention, what is claimed as new and protected by
Letters Patent is:
-12-
