Note: Descriptions are shown in the official language in which they were submitted.
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MICRODEVICE AND METHOD FOR DETECTING A
CHARACTERISTIC OF A FLUILI
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. patent application no.
09/353,554, filed July 14, 1999, which is a continuation-in-part of U.S.
patent application
no. 09/115,397, filed July 14, 199$. This application also claims the benefit
of the filing
date of U.S. provisional patent application no. 60/175,997, filed January 12,
2000. All of
the above U.S. provisional and non-provisional applications are assigned to
the same
assignee and are all herein incorporated by reference in its entirety for all
purposes.
BACKGROUND OF THE INVENTION
Work is now underway to develop microfluidic devices for analyzing
chemical or biological fluids. A "microfluidic" device typically includes
fluid channels
having microscale dimensions. For example, a fluid channel in a typical
microfluidic
device may have a width of less than about 1000 microns.
In a typical application for a microfluidic device, a fluid containing a
chemical compound may flow towards a reaction site on the microfluidic device.
At the
reaction site, the fluid may contact another fluid containing a different
substance. The
characteristics of the resulting fluid passing downstream of the reaction site
may be
detected to determine if the chemical compound reacts with the substance. The
characteristics of the fluid may correspond to, for example, the concentration
of the
chemical compound in the fluid stream. If the concentration of the chemical
compound
in the fluid passing downstream of the reaction site is lower than the
concentration of the
chemical compound upstream of the reaction site, then it is likely that the
chemical
compound reacts with the substance.
Microfluidic analytical systems have a number of advantages over other
types of analytical systems. For example, microfluidic systems are
particularly well
suited for analyzing or reacting samples with low volumes. In a typical
microfluidic
system, samples on the order of nanoliters or even picoliters can be reacted
or analyzed.
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Because of the small volumes of fluids being handled, microfluidic analytical
systems
may be used to rapidly assay large numbers of samples. The assays can be
performed to
study the effect of numerous compounds in various biological processes. For
example,
test compounds that may block, reduce, or enhance the interactions between
different
biological molecules, such as a receptor molecule and a corresponding ligand,
may be
identified as potential candidate drugs.
In recent years, the number of test compounds produced by modern
combinatorial chemistry techniques has dramatically increased. While
conventional
microfluidic systems can be used to test the increasing number of compounds,
the
throughput of such systems could be improved. There is a continuing need to
screen
large numbers of samples quickly and accurately.
Embodiments of the invention address this and other problems.
SUMMARY OF THE INVENTTON
Embodiments of the invention can be used to quickly detect the
characteristics of fluids in a microdevice. Embodiments of the invention can
be used for,
for example, high-throughput drug candidate screening and medical diagnostics.
One embodiment of the invention is directed to a microdevice for
supporting a flowing fluid. The microdevice comprises: a substrate; and a pair
of
generally parallel, spaced wall members on the substrate, wherein at least one
of the wall
members includes a pair of structures defining an opening.
Another embodiment of the invention may be directed to a microdevice
comprising: a substrate; a plurality of wall members; and a plurality of fluid
channels,
wherein each of the fluid channels is defined by adjacent wall members in the
plurality of
wall members, wherein each wall member comprises an opening that is formed by
opposed beveled structures of the wall member and that commuilicates the
adjacent fluid
channels.
Another embodiment of the invention is directed to a method for detecting
a characteristic of a fluid, the method comprising: (a) inserting a probe into
a fluid
channel in a microdevice; (b) detecting a characteristic of a first fluid
flowing in the first
fluid channel; (c) moving the probe from the first fluid channel through an
opening in one
of the walls defining the first fluid channel and to a second fluid channel
adjacent to the
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first fluid channel; and (d) detecting a characteristic of a second fluid
flowing through the
second fluid channel.
Another embodiment of the invention is directed to an analytical assembly
comprising: a detection assembly comprising a plurality of detection devices;
and a
microdevice comprising a plurality of wall members and a plurality of fluid
channels,
wherein each of the fluid channels is defined by adjacent wall members in the
plurality of
wall members.
Another embodiment of the invention is directed to a method for detecting
a characteristic of a fluid, the method comprising: flowing a plurality of
different fluids
through respective fluid channels in a microdevice, each of the fluid channels
in the
microdevice being formed by adjacent pairs of wall members; and detecting
characteristics of the plurality of different fluids substantially
simultaneously using a
plurality of detection devices as the different fluids flow through their
respective fluid
channels.
These and other embodiments of the invention are described in further
detail with reference to the Figures and the Detailed Description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a top view of a microdevice according to an embodiment of
the invention.
FIG. 2 shows a side view of the microdevice shown in FIG. 1 along the
line 2-2.
FIGS. 3(a)-3(c) show partial top views of portions of wall members with
beveled ends.
FIG. 4 shows an end cross-sectional view of the microdevice shown in
FIG. 1 along the line 4-4.
FIG. 5 is a cross-sectional view of the microdevice shown in FIG. I along
the line 5-5.
FIG. 6 is a side cross-sectional view of an analytical system shown in FIG.
7 along the line 6-6.
FIG. 7 is a top cross-sectional view of some components of an analytical
assembly according to an embodiment of the invention. Boundaries forming a
slot in a
cover are shown by dotted lines.
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FIG. 8 is a side cross-sectional view of an analytical assembly according to
an embodiment of the invention.
FIG. 9 is a side cross-sectional view of an analytical assembly according to
an embodiment of the invention.
FIG. 10 is a top cross-sectional view showing some components of an
analytical assembly according to an embodiment of the invention.
FIG. 11 is an end cross-sectional view of an analytical assembly shown in
FIG. 10 along the lines 11-11. Invisible lines show boundaries of a slot in a
cover.
FIG. 12 is a schematic diagram of an analytical assembly embodiment.
FIG. 13 is a top view of an analytical assembly according to an
embodiment of the invention.
FIG. 14 is a graph of surface potential vs. time as a probe scans fluids
flowing in fluid channels in a microdevice according to an embodiment of an
invention.
DETAILED DESCRIPTION
Embodiments of the invention can be used to rapidly detect characteristics
of a plurality of different fluids. The fluids may be gases or liquids.
Exemplary liquids
include biological fluids such as blood or urine, cell extracts, organic
fluids, solvents,
aqueous solutions, and the like. Exemplary gases include air samples,
hydrocarbon gases,
etc. Regardless of the form of the fluids, the fluids may comprise atoms,
organic or
inorganic molecules such as proteins, organelles such as cells, and the like.
The different fluids flow through a plurality of different fluid channels at a
detection region of a microdevice. The different fluids may have distinct
characteristics
and may be the products of events that occur before the different fluids flow
through the
detection region of the microdevice. Fox example, the different fluids may be
downstream products of upstream events such as potential or actual
interactions between
substances. Events may include chemical or biological reactions between two
substances
and binding events between two substances.
Downstream of the events, characteristics of the fluids can be detected at
the detection region of the microdevice. The characteristics of the fluids
that are
detectable may be either quantitative or qualitative in nature. In some
embodiments,
characteristics of the fluids such as emitted radiation (e.g., light),
conductivity, the pH and
the like of the different fluids flowing in the different fluid channels can
be detected to
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analyze the different fluids. Such characteristics may correspond to the types
and/or
amount of substances in the fluids. In some embodiments, the detected
characteristics
may serve as a direct or an indirect indicator of the concentration or amount
of a
particular substance in the fluid. For example, solutions containing protons
are
conductive. The conductivity or resistance of a fluid may be an indirect
indicator of the
concentration of protons in the fluid.
Interactions that can be assayed according to embodiments of the invention
may be any type of interaction normally observed for biological moieties
including, for
example, a catalytic reaction of an enzyme, a binding event, or a
translocation by a
membrane protein through a lipid bilayer. In embodiments of the invention,
separate
fluid samples can be screened for their ability to interact with a biological
moiety. For
example, different fluid samples containing respectively different substances
can flow
through separate fluid channels in a microdevice and can be delivered to
separate reaction
sites on the microdevice. Each of the reaction sites may comprise an
immobilized
biological moiety, and the immobilized moieties may be bound to respective
surfaces of
different fluid channels. At the reaction sites, the biological moieties may
or may not
interact with the different fluid samples. Downstream of the reaction sites,
the
characteristics of the different fluids may be detected, either directly or
indirectly to
determine if any of the fluids of the substances in the different fluids have
interacted (e.g.,
by binding together) with the immobilized biological moiety at each reactive
site. For
example, one or more detection devices downstream of the reactive sites may
measure the
concentration of the different substances in the fluids passing downstream of
the reaction
sites by detecting characteristics of the fluids. If the concentration of a
substance in a
fluid passing downstream of a reaction site is less than the concentration of
the substance
in a fluid upstream of the reaction site, then it is likely that the substance
in the fluid is
interacting (e.g., binding or reacting) with the immobilized biological
moiety. On the
other hand, if the concentration of a substance in a fluid downstream of the
reaction site is
substantially equal to the concentration of the substance upstream of the
reaction site,
then it is likely that little or no interaction is occurring between the
substance in the fluid
and the immobilized biological moiety.
In another example, upstream events may be specific conditions that are
applied to different fluids in the different fluid channels to see if the
fluids or substances
in the fluids change as a result of the conditions. For instance, a plurality
of different
fluids may be subjected to different heating, cooling, and irradiation (e.g.,
with light)
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conditions. Characteristics in the fluids passing downstream of these events
may be
detected to determine if the conditions affect the fluids.
In some embodiments of the invention, characteristics of the different
fluids in the fluid channels may be detected by using a probe. The probe may
pass
through a plurality of different fluids in respective fluid channels by
passing through
openings in wall members that define the fluid channels. The characteristics
of the fluids
in these fluid channels can be quickly detected without exposing the end of
the probe to
an environment outside of the flowing fluid.
In other embodiments of the invention, a plurality of detectors may detect
characteristics of a plurality of fluids flowing through a plurality of fluid
channels in a
microdevice substantially simultaneously. A detection assembly comprising
multiple
detectors may be used to detect the characteristics of the fluids flowing in
the fluid
channels substantially simultaneously. In these embodiments, the wall members
defining
the plurality of fluid channels may or may not have openings.
These and other embodiments are described in further detail below.
I. Embodiments using microdevices
One embodiment of the invention is directed to a microdevice. The
microdevice may include a plurality of fluid channels defined by a plurality
of wall
members. The plurality of wall members may include at least one wall member
having at
least one opening that communicates two adjacent fluid channels. An opening in
the wall
member may be formed by opposing beveled structures at the internal ends of
portions of
the wall member. In embodiments of the invention, different fluids flowing in
the
adjacent fluid channels may have a laminar profile and do not mix in an
appreciable
manner as they flow past the opening and contact each other at the opening.
Intermixing
between the contacting fluids is minimal, even though there is no physical
barner in the
wall member at the opening.
When openings in the respective wall members in the microdevice axe
aligned, a slot may be formed by the aligned openings. A probe disposed in a
fluid in a
fluid channel can move laterally through the slot and from fluid channel to
fluid channel.
For example, the probe can contact a fluid in a fluid channel and can detect a
characteristic of that fluid. The probe can then pass through an opening in a
wall member
defining the fluid channel to an adjacent fluid channel where a characteristic
in the
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adj acent fluid channel may be detected. By analyzing different fluids in this
manner,
characteristics of the different fluids in the fluid channels can be quickly
and accurately
detected by the probe and subsequently analyzed. For example, in some
embodiments,
the characteristics of ten different fluids flowing in the different fluid
channels may be
accurately detected in less than one minute.
Tllustratively, a probe for a pH sensor may be placed in a fluid channel to
detect the pH of the fluid in that channel. Then, the probe can move laterally
from one
fluid channel to another adjacent fluid channel through the openng in a wall
member
disposed between these two fluid channels. The lateral movement of the probe
can take
place without withdrawing the probe from the fluids. Once the probe is in
contact with
the fluid in the adjacent channel, the pH of the fluid in the adjacent channel
can be
detected. This process can be repeated as the probe moves through the slot
formed by the
aligned openings in the wall members.
Embodiments of the invention provide a number of advantages. For
example, in embodiments of the invention, a probe can pass through a number of
fluid
channels and can detect characteristics of the fluids in the fluid channels
quickly and
accurately. The probe need not be withdrawn from the fluid flowing in a
channel and
then inserted into an adjacent fluid channel. The distance that the probe
travels between
adj acent fluid channels is minimized thus reducing the time needed to analyze
the fluids
flowing in the microdevice. Moreover, since a probe need not be withdrawn from
a fluid,
the probe need not be aligned in a z-direction (i.e., relative to a x-y plane
formed by the
orientation of the microdevice) as it moves from fluid channel to fluid
channel. The
z-direction alignment step takes time and increases the chance of damaging the
probe.
For example, if a probe is inserted too far into a fluid channel, the probe
may contact the
fluid channel bottom surface potentially damaging the probe. In embodiments of
the
invention, the probe can be aligned in the z-direction once. To detect the
characteristics
of other fluid streams, the probe may move in an x- or y- direction while
remaining a
predetermined distance above the fluid channel bottoms. Also, by keeping the
probe at a
substantially constant z position, the reliability of measurements conducted
by the probe
can be improved in some instances. For example, the characteristics of a fluid
flowing in
a fluid channel may be a function of insertion depth in a fluid. Keeping a
probe at a
substantially constant z position when detecting characteristics of multiple
fluids can
eliminate any potential variation in any detected characteristics that may be
due to
different probe insertion depths. Furthermore, in embodiments of the
invention, purging
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is not required between two successive detections (e.g., two successive
measurements).
In some conventional microfluidic devices, different fluids to be analyzed
pass through a
single fluid channel. Purging fluids are needed to separate the different
fluids as they
flow in series through the fluid channel. However, in embodiments of the
invention,
different fluids may flow in different, parallel fluid channels at a detection
region in the
microdevice. The fluids in the different fluid chamlels may be detected in
series or in
parallel without using purging fluids. Furthermore, the microdevice
embodiments of the
invention are especially suitable for use with biosensors. Typical biosensors
may contain
biological molecules such as lipids, enzymes, or receptors. If biological
molecules such
I O as these are exposed to air, they may become inactive. Moreover, a typical
biosensor may
have a variable "wetting" period after a sample fluid is applied to the
biosensor. In
embodiments of the invention, a probe can pass between different fluid streams
without
exposing the probe to an external environment such as air. Accordingly, the
microdevice
embodiments of the invention are especially useful for containing fluids that
are to be
analyzed using a biosensor. In addition, since fluid streams can contact each
other yet not
mix in an appreciable manner in embodiments of the invention, reactions at the
interface
of two flowing fluids may be analyzed. One or more probes may detect the
characteristics of a fluid passing downstream of the interface of the two
flowing fluids to
study the interaction between the two fluids.
A microdevice embodiment is shown in FIG. 1. FIG. 1 shows a
microdevice 10 comprising a substrate 12, a plurality of inner wall members
14a-14e, and
a plurality of outer wall members 140,14p. The plurality of inner wall members
14a-14e
is disposed between the outer wall members 140,14p. Both the inner wall
members
14a-14e and the outer wall members 140,14p are disposed on the substrate 12.
In this
example, the inner wall members 14a-14e and the outer wall members 140,14p are
substantially parallel to each other.
The wall members 14a-14e,140,14p are spaced so that each pair of
adjacent wall members 14a-14e,140,14p produces a fluid channel 16a-16d. For
example, adjacent inner wall members 14a,14b produce an inner fluid channel
16a. The
inner wall members 14a,14e and outer wall members 140,14p form outer fluid
channels
160,16p. For example, inner wall member 14a and outer wall member 14p form a
fluid
channel 16p. FIG. 2 shows a side view of the outer wall member 14o and the
substrate 12
of the microdevice 10. In this example, the outer wall member 14o is solid
along its
length and does not have an opening like the inner wall members 14a-14e.
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The fluid channels 16a-d,160,16p in the microdevice 10 shown in FIG. 1
are substantially parallel to each other. However, in other embodiments of the
invention,
the fluid channels and the wall members forming those fluid channels may have
any
suitable configuration. For example, the fluid channels in the microdevice may
be
fabricated so that they are perpendicular or non-linear. Moreover, while the
microdevice
shown in FIG. 1 has six fluid channels, it is understood that in embodiments
of the
invention, the microdevice 10 may have any suitable number of fluid channels.
For
example, in some embodiments, the microdevice 10 may have more than 10, 20 or
50
fluid channels.
10 Each inner wall member 14a-14e can structurally discontinue at an
intermediate region to form an opening 20a-20e. Although the embodiment shown
in
FIG. 1 has one opening 20a-20e per wall member 14a-14e, it is understood that
embodiments of the invention are not limited to microdevices with one opening
per wall
member. For example, each wall member may have 2, 3, 4, or any suitable number
of
openings. Moreover, as will be explained in further detail below, in some
embodiments,
the wall members need not have any openings in them.
In some embodiments, the openings 20a-20e in the members 14a-14e may
be aligned to form a slot 140. The slot 140 formed by the aligned openings 20a-
20e can,
for example, permit a probe (not shown) to pass from one fluid channel to
another fluid
channel without being removed from the microdevice 10. Illustratively, a probe
(not
shown) can detect a characteristic of a first fluid flowing in a first fluid
channel 16a.
After detecting the characteristic, the probe may move through the opening 20b
and into a
second fluid channel 16b. The probe may then detect a characteristic (e.g.,
pH,
conductivity, fluorescence, and/or temperature) in a second fluid flowing in
the second
fluid channel 16b without removing the probe from the microdevice 10. Fluids
in the
other fluid channels I6c,16d,16o may be detected in a similar manner. The
probe need
not be withdrawn from the fluids flowing in the fluid channels 16a-16d,160,16p
and
need not be exposed to the outside environment. By detecting the
characteristics of fluids
in this manner, detection occurs quickly and accurately.
Each inner wall member 14a-14e can include one or more pairs of
opposing beveled structures 24a-24e that form openings 20a-20e in the
respective wall
members 14a-14e. By using beveled structures in a wall member, a fluid having
a
laminar profile flowing in a fluid channel formed by the wall member is more
likely to
retain its laminar profile at the opening formed by the beveled structures.
The beveled
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structures 24a-24e may have any suitable geometry. For example, two examples
of
beveled structures 24a are shown in FIGS. 3(a), 3(b).
In FIG. 3(a), a wall member 14a includes a beveled structure 24a. The
beveled structure 24a includes a pair of tapering walls 28a. In this example,
the tapering
S walls 28a are substantially straight. Also, the tapering walls 28a converge
in an inward
direction to an apex 30 and may form an angle with respect to substantially
parallel side
surfaces 114a of the wall member 14a. The angle may be, for example, from
about 1
degree to about 89 degrees. In other embodiments, the angle may be, for
example, about
2 to about 20 degrees.
FIG. 3(b) shows another example of a beveled structure 24a of a wall
member 14a. The beveled structure 24a also has a pair of tapering walls 28a
that
converge to an apex 30. However, unlike the embodiment shown in FIG. 3(a), the
beveled structure shown in FIG. 3(b) has curved tapering walls 28a. In this
example, the
tapering walls 28(a) curve inwards towaxds the apex 30. The beveled structure
24a
shown in FIG. 3(b) has a generally funnel-shaped appeara~zce when viewed from
the top.
The beveled structure 24a shown in FIG. 3(c) is similar to the previously
shown beveled
structures, but includes a smooth transition between the side surfaces 114(x)
and the
tapering walls 28(a). As shown, side surfaces 114(x) may be substantially
parallel to
each other and may then gradually curve inwardly in the region of the tapering
walls
28(a).
The particular geometries of the features of the microdevice 10 may vary.
Examples of features include wall member thicknesses, fluid channel heights,
and fluid
channel widths. Typically, the features of the microdevice 10 have at least
one dimension
that is less than about 1000 microns. For example, in some embodiments, the
width and
2S depth of each fluid channel may be between about 10 microns and about S00
microns. In
other embodiments, the width or depth of each fluid channel may be between
about SO
microns and about 200 microns. In some embodiments, the fluid channels may
sometimes be referred to as "microchannels".
Refernng to FIG. 4, each wall member 14a-14e,140,14p may have a
width "W" of less than about 1 mm (e.g., about 20 microns to about 100
microns) and a
height "D" of less than about 1 mm. In some embodiments, D may be from about
SO
microns to about S00 microns (e.g., about 200 microns). Each fluid channel 16a-
16d,
160,16p may have a width "w" of less than about 1 mm (e.g., about S0, 100, 1
S0, or 200
microns).
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Referring to FIG. 5, the distance "G "of each opening 20a formed in a wall
member 14a may be about 1 mm or less. For example, in some embodiments, G may
be
from about 50 microns to about 400 microns (e.g., about 200 microns). As shown
in FIG.
5, the wall member 14a structurally discontinues to form an opening ZOa so
that the wall
member 14a has two distinct, separated portions. Each portion of the wall
member 14a
may have two parts. One part may have substantially parallel sidewalls and may
have a
length "L1" or "L2". The other part may be a beveled structure that extends
along the
length of the wall member 14a a distance "S". Typically, the distance L1 or L2
is much
greater than the length S. For example, the distance L1 or L2 may be about 1
cm or more
(e.g., about 1 cm to about 5 cm). The length S may be about 50 microns to
about 750
microns. Of course, the dimensions of the elements of the microdevice 10 may
have
values that are more or less than the specifically mentioned values.
Again referring to FIG. 1, the fluid channels 16a-16d,160,16p may have
any suitable length or configuration. The length of each fluid channel 16a-
16d,160,16p
may be from about 1 to about 20 mm in length, or more. For example, the length
of each
fluid channel 16a-16d,160,16p can be from about 2 to about 8 mm. The distance
between the corresponding points (e.g., opposing apexes) of opposed beveled
structures
in a wall member may be between about 50 and about S00 microns in some
embodiments.
Any channel cross-section geometry (trapezoidal, rectangular, v-shaped,
semicircular,
etc.) can be employed in the microdevice 10. Trapezoidal or rectangular cross-
section
geometries may be used in the fluid channels 16a-16d,160,16p. Such geometries
may
be used with standard fluorescent detection methods.
Fluids such as liquids or gases may be supplied to the microdevice 10 in
any suitable manner. For example, bulk-loading dispensing devices can be used
to load
all fluid channels 16a-16d,160,16p of the microdevice 10 at once with the same
or
different fluids. Alternatively, integrated or non-integrated microcapillary
dispensing
devices may be used to load fluids separately into each fluid channel 16a-
16d,160,16p
of the microdevice 10.
The flow of the fluids within the fluid channels 16a-16d,160,16p can be
controlled by the selective application of voltage, current, or electrical
power to the
substrate to induce and/or control the electrokinetic flow of the fluids.
Alternatively or
additionally, fluid flow may be induced mechaxucally through the application
of, for
example, differential pressure or acoustic energy to a fluid. Such fluid flow
control
mechanisms are used in microfluidic devices and are known in the art.
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As noted, each of the fluids flowing in the fluid channels 16a-16d,160,
16p may have a laminar profile. In this regard, the Reynolds number, Re, for
the fluid
streams in the fluid channels 16a-16d,160,16p may be greater than 0 to less
than or
equal to about 2300. Preferably, Re is from about 100 to about 2000. Re may be
defined
as follows:
Re = ~ cave Dh
p is the density in gxn/cm3, ~, is viscosity in gm/cm~sec, Va..e is the
average velocity of the
fluid, and Dh is the hydraulic diameter. The hydraulic diameter, Dh, may be
defined as
follows:
4xCross -SectiohArea (~yylz)
D~~ (cm)
Wetted Perimeter (cm)
Although the fluids in the channels preferably have a laminar profile,
adjacent fluids
flowing in adjacent fluid channels may slightly intermingle (e.g., by
diffusion) via the
opening that communicates the adjacent fluid channels. However, the degree of
intermingling between fluids in adjacent fluid channels does not typically
interfere with
any measurements or detections made by a probe.
Although many of the previously described examples have different
sample fluids flowing through the fluid channels 16a-16d,160,16p in the
microdevice
10, in other embodiments of the invention, non-sample fluids such as wash
fluids may be
included in one or more of the fluid channels 16a-16d,160,16p. For example, a
wash
fluid that can be used to wash a probe may flow through one or more fluid
channels
16a-16d,160,16p. For example, a fluid channel 16c containing a wash solution
is
disposed between two fluid channels 16b,16d containing sample fluids. A probe
(not
shown) may be inserted into the fluid channel 16b to detect a characteristic
of a sample
fluid flowing in the fluid channel 16b. To detect a characteristic, the probe
may be, for
example, positioned in fluid channel 16b between the openings 20b, 20c or may
be
upstream or downstream of the point between the openings 20b, 20c. After
detecting the
characteristic, the probe may pass through the opening 20c in the wall member
14c to the
fluid channel 16c containing a wash fluid. In the fluid channel 16c, the wash
fluid
removes any materials that may be disposed on the probe and that may impede
the
probe's ability to detect a characteristic in a different fluid. After the
probe is washed, the
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washed probe may pass through the opening 20d in the wall member 14d to the
other
fluid channel 16d containing the other sample fluid. The washed probe can then
detect a
characteristic of the sample fluid in the fluid channel 16d. Alternatively or
additionally,
one or more of the fluid channels 16a-16d,160,16p may contain a calibration
fluid that
can be used to calibrate, for example, a probe. The probe can be calibrated
while being
disposed in a calibrating fluid and may move to a fluid channel with a sample
fluid after
the probe is calibrated.
FIG. 6 shows an analytical assembly comprising a probe assembly 46 and
a microdevice 10. The microdevice 10 in FIG. 6 is similar to the previously
described
microdevice 10 shown in FIG. l, except that the microdevice 10 shown in FIG. 6
includes
a cover 36. The cover 36 may also comprise a plurality of fluid inlets (not
shown) and a
plurality of fluid outlets (not shown) that provide fluids to and remove
fluids from the
fluid channels 16a-16d,160,16p in the microdevice 10.
The cover 36 is supported by the pair of outer wall members 140,14p and
rnay include a slot 40. A pair of opposed, generally parallel, boundaries may
define the
slot 40 in the cover 36. When the cover 36 is disposed on the wall members,
the slot 40
in the cover 36 is aligned with and disposed over the slot 140 formed by the
holes
20a-20e in the inner wall members 14a-14e (see FIG. 1). The boundaries
defining the
slot 40 in the cover 36 may or may not be generally aligned with apexes of the
beveled
structures in the wall members 14a-14e. A probe 44 of a probe assembly 46 is
inserted
through the slot 40 in the cover 36 so that an end portion 47 of the probe 44
is disposed in
a fluid channel 16a and in the slot 140 in microdevice 10.
In the analytical assembly shown in FIG. 6, the probe 44 may include an
intermediate portion 45 that is upright and an end portion 47 that is skewed
with respect
to the intermediate portion 45. The end portion 47 of the probe 40 may be
substantially
perpendicular to the intermediate portion 45. In other embodiments, the end
portion of
the probe need not be perpendicular to an intermediate portion of the probe.
For example,
in some embodiments, the end portion of a probe may be co-linear with an
intermediate
portion of the probe.
In this example, the end portion 47 of the probe 44, is directed towards the
upstream direction of the fluid flowing (which flows in direction A) through
the fluid
channel 16a. As the fluid flows through the fluid channel 16a, the end portion
47 of the
probe 44 may receive some of the fluid flowing in the fluid channel 16a. Once
the fluid
is received, the end portion 47 may remove a portion of the fluid for
sampling. For
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example, the probe 44 associated with the probe assembly 46 may include a
micro-pipe
that collects some of the fluid flowing through the fluid channel 16a. Once
collected, the
sample may then be transferred to a mass spectrometer, HPLC (high pressure
liquid
chromatography) apparatus, or a gas chromatography apparatus. In some
embodiments,
the micro-pipe could also be used to introduce a fluid into a fluid channel.
The
introduced fluid can be added to a fluid channel without disturbing the
laminar flow
profile in the flowing fluid. Other suitable detection assemblies, detection
devices, and
analytical systems according to embodiments of the invention are described in
further
detail below.
Refernng to FIGS. 6 and 7, to move the probe 44 from fluid channel to
fluid channel, the probe 44 may move in the desired direction in the slot 40,
such as in
direction of arrow B (see FIG. 7). Because the end portion 47 in this example
protrudes
from the upright portion 45 of the probe 44, in order to pass the end portion
47 through
the slot 40, the end portion 47 may be initially aligned with the slot 40 and
may then be
I S inserted through the slot 40 in the cover (not shown in FIG. 7). Once the
end portion 47
is in the slot 140 formed by the openings 20a-20e in the wall members 14a-14e,
it is
rotated about 90° in direction of the arrow C shown in FIG. 7 so that
the end portion 47 is
directed toward the flowing fluid in the fluid channel in which it is
disposed. The
boundary 40a at slot 40 may be aligned with the apexes 30a-30e of the wall
members
14a-14e so that the end portion 47 of the probe 40 does not contact the apexes
30a-30e as
the probe 44 is inserted into the slot 40.
FIG. 8 shows another analytical assembly embodiment of the invention.
In this embodiment, the microdevice 10 includes a cover 36 having slot 40. A
lid 50 is on
the cover 36 and is spaced from the cover 36 by supports (not shown). The slot
40 in the
cover 36 is defined by downwardly sloping planar surfaces from boundaries 40a
and 40b
that terminate in edges 58a and 58b, respectively. The lid 50 also has a slot
60 that is
generally aligned with the slot 40 in the cover 36. The probe 44 may pass
through both
the slot 60 in the lid 50 and the slot 40 in the cover 36.
The embodiment shown in FIG. 8 can be used when the fluids flowing
through the fluid channels are gases. As gases flow through the fluid channels
defined by
the wall members and the substrate, another gas such as an inert gas (e.g., a
noble gas,
nitrogen, etc.) flows between the lid 50 and cover 36. The inert gas may flow
in a
direction of the arrow D and may have a higher pressure than the gases flowing
through
the fluid channels formed by the wall members on the substrate 12. The higher
pressure
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gas flowing between the lid 50 and the cover 36 confines gases flowing in the
fluid
channels between the cover 36 and the substrate 12 and prevents diffusion of
the same out
of the fluid channels and into the zone between the lid 50 and the cover 36.
In the
embodiment shown in FIG. 8, the probe assembly 46 has a probe 44 with a
beveled end
and not a protruding end portion as in the previous examples. The probe
assembly in the
embodiment shown in FIG. 8 could also have a protruding end portion if
desired.
FIG. 9 shows another analytical assembly embodiment of the invention.
The microdevice 10 in this embodiment has a substrate 12, a bottom member 80,
a slide
member 90, a cover 36, and a probe assembly 46, and a probe 44. The bottom
member
80 has a passage 82 where the slide member 90 is disposed. The slide member 90
may
slide in a direction transverse to the orientation of the fluid channels 16a-
16e,160,16p
(i.e., in direction of the arrow E in FIGS. 10 and 11). As shown in FIGS. 10
and 11, the
substances 94 disposed on the slide member 90 may be aligned with the fluid
channels
16a-16e,160,16p so that the fluids flowing within the fluid channels 16a-
16e,160,16p
come in contact with the substances 94.
Illustratively, with reference to FIG. 9, the slide member 90 may support
substances 94 that can contact a fluid flowing through the fluid channel 16a
prior to
reaching the probe 44 of the probe assembly 46. The characteristic of the
fluid in the
fluid channel 16a can be detected after the fluid has contacted the substances
94 on the
slide member 90. For example, the substances 94 may comprise antibodies for
capturing
molecules contained in the fluid flowing in the fluid channel 16a. The probe
44 may then
contact the downstream fluid and the probe 44 can detect a characteristic of
the
downstream fluid. The concentration of the molecules in the fluid can then be
determined. If the concentration of the molecules upstream of the slide member
90 is
greater than the concentration of the molecules downstream of the slide member
90, then
it can be concluded that the substances 94 on the slide member 90 interact
with the
molecules in the fluid.
Ln some embodiments, the microdevice IO can be used to deposit
successive layers of material on a slide member 90. This may be done by
pulling the
slide member 90 through the passage 82 in the rnicrodevice 10. The slide
member 90
may be exposed to a succession of many different fluids that may deposit
different
materials on the slide member 90.
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II. Detection assemblies and analytical systems
The detection methods, detection assemblies, and analytical systems used
in embodiments of the invention are not limited to those described above, and
may
employ any suitable optical, electrical, physical, and/or chemical detection
techniques.
Radiation such as visible, infrared, or ultraviolet radiation from the fluids
may be detected
by a detection assembly being an optical detection assembly.
In many of the embodiments described above, detection assemblies and
analytical systems using probes that comprise micropipes are described in
detail.
However, embodiments of the invention are not limited to the use of such
micropipes.
For example, the end portion of a probe may contact the fluid flowing in a
fluid channel
to detect a particular characteristic of the fluid, without collecting a
sample of the fluid.
The probe may be coupled to signal analyzer (such as that sold by Hewlett-
Packard, for
example), an oscilloscope (such as that sold by Tektronix or Hewlett-Packard),
or a lock-
in amplifier (such as that commercially employed by Stanford Research System
or
EG&G).
The probe may comprise a physical sensor, a biological sensor, a chemical
sensor, or an electrical sensor. Examples of physical sensors include
thermocouples,
pressure sensors, flow sensors, optical fibers, etc. Examples of biological
sensors include
sensors with immobilized enzymes or immunoassays. Examples of electrical or
chemical
sensors include sensors with interdigitated electrodes having optional polymer
coatings,
atomic force microscopes (AFMs), Ion Sensitive Field Effect Transistors
(ISFETs), light
addressable potentiometric sensors (LAPSs), pH meters, and scanning probe
potentiometers (SPPs). These and other types of sensors are described in
Manalis et al,
Applied Physics Letters, Volume 76, No. 8, February 21, 2000, and other
references. In
comparison to optical detection devices, chemical sensors and electrical
sensors are
desirable as they do not need to use more expensive and inconvenient
fluorescent or
radiochemical tagging processes.
An atomic force microscope allows high force sensitivity mapping of
biological cells and molecules such as DNA and proteins. The AFM can obtain
stable
images of individual biomolecules while operating in physiological
environments. In an
AFM, unlike optical detection devices, molecules can be imaged directly, and
the
dimensions of the probe can determine the spatial resolution.
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Field effect devices such as the ISFET and the LAPS can directly detect
molecular and ionic charge. For example, the LAPS device has been used in a
microphysiometer to monitor the response of cells to chemical substances by
measuring
the rate of change of the pH as protons are excreted from cells during
metabolism.
LAPS devices may be commercially obtained from Molecular Devices of Sunnyvale,
CA.
Preferably, the active areas of electrical detection devices such as AFMs,
ISFETs, and SPPs are small. In some embodiments, the active area in such
detection
devices is less than about a square millimeter, or less than 100 square
microns. When the
active area is small, the detection sensitivity and resolution is improved in
comparison to
detection devices with larger active areas.
Other detection devices may be used instead of or in addition to one or
more probes. In some embodiments, detection devices such as one or more
optical
detection devices may be used to detect the characteristics of fluids flowing
in the fluid
channels in a microdevice. For example, FIG. 12 shows a schematic diagram of
an
analytical assembly comprising a detection assembly that detects fluorescent
light coming
from the fluids on a microdevice. In the illustrated detection assembly, the
microdevice
121 is positioned on a base plate 120. Light from a 100W mercury arc lamp 125
is
directed though an excitation filter 124 and onto a beam splitter 123. The
light is then
directed through a lens 122, such as a Micro Nikkor 55 mm 1:2:8 lens and onto
the fluids
flowing in the fluid channels of the microdevice 110. Fluorescence emission
from the
device returns through the lens 122 and the beam splitter 123. After also
passing though
an emission filter 126, the emission is received by a cooled CCD camera 127,
such as the
Slowscan TE/CCD-10245F&SB (Princeton Instruments). The camera 122 is operably
connected to a CPU 128, which is, in turn, operably connected to a VCR 129 and
monitor
130.
In some embodiments of the invention, the analytical assembly may
comprise a detection assembly comprising a plurality of detection devices and
a
microdevice. The microdevice may comprise a plurality of wall members and a
plurality
of fluid channels, wherein each of the fluid channels is defined by adjacent
wall members
in the plurality of wall members. The analytical assembly may be used to
detect
characteristics of different fluids flowing in different fluid channels
substantially
simultaneously. In these embodiments, the wall members of the microdevice may
or may
not have openings that allow adjacent fluid channels to communicate with each
other. By
using multiple detection devices, the characteristics of fluid flowing in the
fluid channels
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of a microdevice may be detected in parallel, thus increasing the speed of
detection and
analysis.
In one example, a plurality of different biological moieties can be screened
in parallel for their ability to interact with a component of a fluid sample.
A fluid sample
can be delivered to the reactive sites in fluid channels in a microdevice
where each of the
different biological moieties is immobilized on a different site of the
microdevice. Then,
characteristics of the fluids passing downstream of the reactive sites may be
detected
substantially in parallel with a plurality of detection devices to study the
interaction of the
component with the immobilized biological moieties at each reactive site.
Illustratively, referring to FIG. 13, a slide member 90 may comprise a
number of detection devices such as sensors 194 and may form a detection
assembly.
The sensors 194 on the slide member 90 may contact the fluids flowing in the
fluid
channels 16a-16e,160,16p and may subsequently detect characteristics of the
fluids.
The sensors 194 may be, for example, conductivity sensors, biosensors,
temperature
sensors, etc. In these embodiments, a probe assembly with an elongated probe,
and a
cover with a slot for the elongated probe are not needed.
Other detection assemblies with multiple detection devices may be used in
embodiments of the invention. For example, probe assemblies like the probe
assembly 46
shown in FIG. 6 can be used. The probe assembly, however, may comprise two or
more
elongated probes 44. These probes may be spaced so that they can be inserted
into plural
fluid channels simultaneously to detect characteristics of the fluids flowing
in these fluid
channels substantially simultaneously. In some embodiments, the number of
probes in
the detection assembly may be equal to or less than the number of fluid
channels in the
microdevice. For example, if a microdevice has six fluid channels, a probe
assembly
with six probes that are insertable within the six fluid channels can be used
to
substantially simultaneously detect characteristics of the six fluids flowing
in the six fluid
channels.
In another example, a plurality of optical detectors may be positioned to
receive optical signals coming from a plurality of fluids flowing in their
respective fluid
channels on a microdevice. For example, the plurality of optical detectors may
comprise
a charge coupled device (CCD) array or a photodiode array. These arrays may be
positioned to receive optical signals coming from the fluids flowing in the
fluid channels.
In some embodiments, radiolabels or fluorescent tags on molecules in fluids
flowing in
the fluid channels in a microdevice may provide such optical signals.
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III. Exemplary methods of manufacture
The microdevices according to embodiments of the invention may be
made according to any suitable process. For example, in some embodiments,
portions of
a body of material may be removed to form a plurality of wall members. In
these
embodiments, the wall members may be integrally formed with the substrate.
Examples
of suitable material removal processes include bulk micromachining,
sacrificial
micromachining, focused ion-beam milling, electrostatic discharge machining,
ultrasonic
drilling, laser ablation, mechanical milling and thermal molding techniques.
Conventional photolithographic and etching processes may be used to etch a
body to form
a plurality of wall members and fluid channels in the body. Etching processes
such as
reactive ion etching (RIE) or deep reactive ion etching (DRIE), or wet etching
may be
used to etch an appropriate body of material. In some embodiments, the wall
members
and the underlying substrate may be formed by molding. In other embodiments,
wall
members may be formed on a substrate. For example, wall members may be formed
on
or bonded to a body to form a plurality of fluid channels. For example, wall
members
may be formed by electroplating (e.g., lugh aspect ratio plating).
If desired, after the fluid channels are formed in the microdevice, the
surfaces defining the fluid channels may be coated with a material. The
material coated
on the walls or bottom surfaces defining the channels may be an adhesion
layer, coupling
agents, or substances that may potentially interact with fluids flowing
through the fluid
channels.
Any suitable material may be used as to form the substrate acid the wall
members in the microdevice. The materials used may be organic or inorganic,
and may
be transparent, translucent, or non-transparent. Materials that can be
micromachined or
microfabricated axe preferred. Suitable micromachinable materials include
silicon, glass,
plastic and the like. Other suitable materials, and processes for forming a
plurality of
fluid channels in a microdevice may be found in U.S. Patent Application No.
09/115,397,
which is assigned to the same assignee as the present application, and
International
Application No. PCT/LTS99/1596~. Both of these applications are herein
incorporated by
reference in their entirety for all purposes.
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EXAMPLE
A microdevice having ten fluid channels was fabricated by forming nine
wall members in a silicon substrate. The wall members were formed in a silicon
substrate
using a deep reactive ion etch. Each of the wall members had an opening and
the
openings in the wall members were aligned to form a slot that passed across
the nine wall
members. The height of the wall members and the corresponding channel depth
was
about 200 microns. The width of each of the fluid channels was 110 microns,
and the
channel pitch was about 150 microns.
Buffered solutions with pH values of 4, 7, and 10 were fed to the different
fluid channels in the microdevice. Because the fluid channel volumes were low,
the
Reynolds number for the solutions in the fluid channels was sufficiently low
to maintain
laminar flow at reasonable flow rates. With laminar flow, the solutions
flowing in the ten
fluid channels did not mix in the slot region of the microdevice. The flow
rates for the
solutions in the fluid channels were set for a maximum value of 500
nanoliters/minute.
The pH values of the different fluids flowing in the ten fluid channels were
measured using a scanning probe potentiometer (SPP). The SPP had a probe was
insertable into a fluid channel and had a sensitivity of less than 0.01 pH
units and a spatial
resolution of 10 microns.
The pH of the ten fluids flowing in the ten fluid channels was profiled by
measuring the pH in a fluid channel proximate one side of the microdevice.
After the pH
values in this fluid channel are measured, the probe moves through the slot to
the next
adjacent fluid channel without removing the pH sensitive area of the probe
from the
flowing fluids. The pH value of the adj acent fluid channel was then measured.
The pH
values of the fluids in the remaining eight fluid channels were measured in a
similar
manner. The travel time between the fluid channels was about 1 second. The
measurement time was about 5 seconds per channel.
A plot of sensor potential versus time during the scanning process is
shown in FIG. 14. The relative potential difference between each fluid chamlel
correlates
closely to the actual pH values of the fluids in the channels (listed above
the plot), except
for the first and last edge channels. Each of the plateaus in the plot
corresponds to a pH
measurement of a fluid in a fluid channel. As shown in the plot, the time used
to measure
the pH values of the ten fluids in the ten fluid channels was less than one
minute.
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All patents, patent applications, and publications mentioned above are
herein incorporated by reference in their entirety. The citation of such
documents is not
an admission such patents, patent applications, and publications are prior
art.
The terms and expressions which have been employed herein are used as
terms of description and not of limitation, and there is no intention in the
use of such
terms and expressions of excluding equivalents of the features shown and
described, or
portions thereof, it being recognized that various modifications are possible
within the
scope of the invention claimed. lVloreover, any one or more features of any
embodiment
of the invention rnay be combined with any one or more other features of any
other
embodiment of the invention, without departing from the scope of the
invention. For
example, any feature of the embodiments using multiple detection devices may
be used
with any feature of the embodiments using wall members with openings without
departing from the scope of the invention.
21
