U.S. patent application number 11/497464 was filed with the patent office on 2006-11-23 for alignment of multicomponent microfabricated structures.
Invention is credited to Richard J. McReynolds, J. Wallace Parce, Jeffrey A. Wolk.
Application Number | 20060261033 11/497464 |
Document ID | / |
Family ID | 23121934 |
Filed Date | 2006-11-23 |
United States Patent
Application |
20060261033 |
Kind Code |
A1 |
Wolk; Jeffrey A. ; et
al. |
November 23, 2006 |
Alignment of multicomponent microfabricated structures
Abstract
Multilayered microfluidic devices include structures that are
used to align elements that make up the devices. Such elements
include additional substrate layers, external sampling elements,
and the like. In one embodiment, a multilayered microfluidic device
includes first and second substrate layers attached one to the
other, each substrate layer having a notch in an edge of the
substrate layer. The notches are positioned such that they
circumscribe a single opening into which an alignment key is
inserted. In a method of fabricating a multilayered microfluidic
device, notches are provided in first and second substrate layers,
the notches circumscribing a single opening when the substrate
layers are mated together. An alignment key is inserted into the
single opening, and the substrate layers are bonded together. The
alignment key may be, for example, a shim or a capillary
element.
Inventors: |
Wolk; Jeffrey A.; (Half Moon
Bay, CA) ; McReynolds; Richard J.; (San Jose, CA)
; Parce; J. Wallace; (Palo Alto, CA) |
Correspondence
Address: |
CALIPER LIFE SCIENCES, INC.
605 FAIRCHILD DRIVE
MOUNTAIN VIEW
CA
94043-2234
US
|
Family ID: |
23121934 |
Appl. No.: |
11/497464 |
Filed: |
July 31, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09966863 |
Sep 28, 2001 |
|
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11497464 |
Jul 31, 2006 |
|
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09291808 |
Apr 14, 1999 |
6322683 |
|
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09966863 |
Sep 28, 2001 |
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Current U.S.
Class: |
216/2 |
Current CPC
Class: |
B01L 2400/0415 20130101;
B01L 2400/0487 20130101; B01L 3/502707 20130101; B01L 2300/0816
20130101; B01L 2300/0887 20130101 |
Class at
Publication: |
216/002 |
International
Class: |
C23F 1/00 20060101
C23F001/00 |
Claims
1. A method of fabricating a multilayered microfluidic device,
comprising: providing a first notch in an edge of a first substrate
layer; providing a second notch in an edge of a second substrate
layer, the first and second notches being positioned such that the
first and second notches circumscribe a single opening when the
first and second substrate layers are mated in a first relative
position; inserting an alignment key into the single opening, the
alignment key being configured to fit into the single opening; and
bonding the first substrate layer to the second substrate layer in
the first relative position.
2. The method of claim 1, wherein the first and second notches are
rectangular.
3. The method of claim 1, wherein one of the first substrate layer
and the second substrate layer comprises a groove fabricated into a
surface thereof, the groove terminating in one of the first and the
second notch, and wherein the alignment key comprises a capillary
element.
4. The method of claim 3, wherein the capillary element includes a
capillary channel running its length.
5. The method of claim 4, wherein inserting the alignment key into
the single opening places the capillary channel into fluid
communication with the groove.
6. The method of claim 3, wherein the capillary element is
rectangular.
7. The method of claim 3, wherein the capillary element is bent
such that a portion of the capillary element is not collinear with
the groove when the capillary element is inserted into the single
opening.
8. The method of claim 1, wherein the alignment key comprises a
shim.
9. The method of claim 1, wherein each notch is from about 10 .mu.m
to about 50 .mu.m in depth.
10. The method of claim 1, wherein each notch extends into the
substrate layer up to about 2 mm.
11. The method of claim 1 wherein one of the first substrate layer
and the second substrate layer comprises first and second
intersecting grooves fabricated into a surface thereof, wherein the
intersecting grooves form intersecting channels when the first
substrate layer is bonded to the second substrate layer.
12. The method of claim 1 wherein the notches are formed using
photolithographic techniques.
13. A multilayered microfluidic device, comprising: a first
substrate layer having a first notch in an edge of the first
substrate layer; a second substrate layer attached to the first
substrate layer, the second substrate layer having a second notch
in an edge of the second substrate layer, the first and second
notches being positioned such that the first and second notches
circumscribe a single opening; and an alignment key inserted into
the single opening.
14. The device of claim 13, wherein one of the first substrate
layer and the second substrate layer comprises a groove fabricated
into a surface thereof, the groove terminating in one of the first
and the second notch, and wherein the alignment key comprises a
capillary element having a channel in fluid communication with the
groove.
15. The device of claim 14, wherein the first and second notches
and the capillary element are rectangular.
16. The device of claim 14, wherein the capillary element is bent
such that a portion of the capillary element is not collinear with
the groove.
17. The device of claim 13, wherein one of the first substrate
layer and the second substrate layer comprises first and second
intersecting grooves fabricated into a surface thereof.
18. The device of claim 17, wherein one of the first substrate
layer and the second substrate layer comprises first and second
apertures in fluid communication with the first and second
intersecting grooves.
19. The device of claim 17, wherein at least one of the grooves
terminates in one of the notches, and wherein the alignment key
comprises a capillary element having a channel in fluid
communication with the groove terminating in the notch.
20. The device of claim 19, wherein the capillary element is bent
such that a portion of the capillary element is not collinear with
the groove terminating in the notch.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/966,863, filed Sep. 28, 2001, which is a
divisional of U.S. patent application Ser. No. 09/291,808, filed
Apr. 14, 1999, both of which are incorporated herein by reference
in their entirety for all purposes.
BACKGROUND OF THE INVENTION
[0002] The field of microfluidics has been held up as the next
great advance in biological science, akin to the advances made in
the electronics industry with the development of the
microprocessor. In particular, the small scale, high level of
accuracy and reproducibility, and ready automatability have led to
expectations that this field of research will revolutionize the way
work is done in research laboratories.
[0003] As with the electronics industry, incremental advances will
be achieved as the operations performed by these microfluidics
systems are expanded and optimized in accordance with their
increasing acceptance in the scientific area. However, also as with
the electronics industry, the most significant developments in this
technology will likely not involve incremental advances in specific
operations, but will instead revolve around advances in the
technology used to fabricate these systems. In particular, some of
the most significant advances in the electronics industry have come
from improved methods of producing microchips, which allow
substantially increased efficiency and greater functionality in a
smaller area or space.
[0004] Fabrication of microfluidic systems typically involves the
fabrication of grooves in the surface of a first substrate layer,
which grooves will correspond to the channel network in a finished
microfluidic device. A second substrate layer is overlaid and
bonded to the first to seal the grooves thereby forming the
channels. Apertures disposed in one of the substrates communicate
with the channels and function as access ports and or reagent
reservoirs for the devices. With certain exceptions, this
fabrication process has been largely unimproved for some time.
Commonly owned U.S. Pat. No. 5,882,465, to McReynolds, for example
describes improved methods of mating and bonding the various
substrate layers together in order to improve fabrication
efficiency. Similarly, Published International Patent Application
No. WO 98/00705 describes methods for fabricating microfluidic
devices used in high throughput assay applications.
[0005] The present invention provides additional improvements in
the fabrication of microfluidic devices, which improvements improve
the efficiency both of the fabrication processes and operations to
be performed by microfluidic devices.
SUMMARY OF THE INVENTION
[0006] In a first aspect, the present invention provides a
microfluidic device comprising a first substrate layer with at
least a first planar surface. The first planar surface has at least
a first microscale groove fabricated therein. The groove terminates
at at least one end in a well also fabricated into the first
surface. A second substrate layer comprising at least a first
aperture disposed therethrough is also part of the device. The
aperture is of smaller dimensions than the well. The second
substrate layer is mated with the first surface of the first
substrate layer to cover the groove and positioned such that the
aperture is in complete communication with the well.
[0007] Another aspect of the present invention is a method of
fabricating a microfluidic device. First and second substrate
layers are provided. A microscale groove is fabricated into at
least a first surface of at least one of the first and second
layers. Concurrently, an alignment structure is fabricated into the
at least one surface of the first or second layers at a desired
position relative to the microscale groove. One or more of a third
component of the microfluidic device and a tool is mated with the
alignment structure to align the third component or the tool
relative to the microscale groove.
[0008] A further aspect of the present invention is a method of
fabricating a multilayered microfluidic device. A first substrate
layer includes a first notch. A second notch is included in a
second substrate layer. The first and second notches are positioned
to be complementary when the first and second substrate layers are
mated together. An alignment key is inserted into one of the first
and second notches. The alignment key is configured to fit into the
first and second notches when the first and second substrate layers
are mated together and aligned in a first relative position. The
first substrate layer is mated and bonded to the second substrate
layer in the first relative position.
BRIEF DESCRIPTION OF THE FIGURES
[0009] FIG. 1 schematically illustrates microfluidic device
comprised of a plurality of substrate layers where the microscale
channel network is defined between the substrate layers.
[0010] FIG. 2 schematically illustrates the influences of substrate
alignment on channel configuration.
[0011] FIG. 3 illustrates the use of alignment facilitating
structures in accordance with the present invention, and
particularly the use of wells to minimize the effects of
misalignment of reservoirs in a multi-layered device structure.
[0012] FIG. 4 illustrates one example of a microfluidic device that
includes an external sampling pipettor element.
[0013] FIG. 5 illustrates a microfluidic device coupled with
appropriate controller and detector instrumentation for accessing
externally stored materials.
[0014] FIG. 6 illustrates an alignment structure for use in
facilitating the fabrication of additional elements on a substrate
of a microfluidic device, e.g., for drilling holes through the
substrate.
[0015] FIG. 7 illustrates the use of an alignment key in the
fabrication of microfluidic devices. As illustrated, the alignment
key is also an external pipettor element.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present invention is generally directed to microfluidic
devices and systems, and improved methods of manufacturing these
devices and systems. In particular, the methods of the present
invention facilitate the manufacture of microfluidic devices by
facilitating either the fabrication of elements on those devices or
the joining of additional elements to those devices, and
particularly to the microscale channel networks contained
therein.
[0017] As used herein, the term "microscale" or "microfabricated"
generally refers to structural elements or features of a device
which have at least one fabricated dimension in the range of from
about 0.1 .mu.m to about 500 .mu.m. Thus, a device referred to as
being microfabricated or microscale will include at least one
structural element or feature having such a dimension. When used to
describe a fluidic element, such as a passage, chamber or conduit,
the terms "microscale," "microfabricated" or "microfluidic"
generally refer to one or more fluid passages, chambers or conduits
which have at least one internal cross-sectional dimension, e.g.,
depth, width, length, diameter, etc., that is less than 500 .mu.m,
and typically between about 0.1 .mu.m and about 500 .mu.m. In the
devices of the present invention, the microscale channels or
chambers preferably have at least one cross-sectional dimension
between about 0.1 .mu.m and 200 .mu.m, more preferably between
about 0.1 .mu.m and 100 .mu.m, and often between about 0.1 .mu.m
and 20 .mu.m. Accordingly, the microfluidic devices or systems
prepared in accordance with the present invention typically include
at least one microscale channel, usually at least two intersecting
microscale channels, and often, three or more intersecting channels
disposed within a single body structure. Channel intersections may
exist in a number of formats, including cross intersections, "T"
intersections, or any number of other structures whereby two
channels are in fluid communication.
[0018] The body structure of the microfluidic devices described
herein typically comprises an aggregation of two or more separate
layers which when appropriately mated or joined together, form the
microfluidic device of the invention, e.g., containing the channels
and/or chambers described herein. Typically, the microfluidic
devices described herein will comprise a top portion, a bottom
portion, and an interior portion, wherein the interior portion
substantially defines the channels and chambers of the device.
[0019] FIG. 1 illustrates an example of a two-layer body structure
10, for a microfluidic device. As shown, the bottom portion of the
device 12 comprises a solid substrate that is substantially planar
in structure, and which has at least one substantially flat upper
surface 14. A variety of substrate materials may be employed as the
bottom portion. Typically, because the devices are microfabricated,
substrate materials will be selected based upon their compatibility
with known microfabrication techniques, e.g., photolithography, wet
chemical etching, laser ablation, air abrasion techniques,
injection molding, embossing, and other techniques. The substrate
materials are also generally selected for their compatibility with
the full range of conditions to which the microfluidic devices may
be exposed, including extremes of pH, temperature, salt
concentration, and application of electric fields. Accordingly, in
some preferred aspects, the substrate material may include
materials normally associated with the semiconductor industry in
which such microfabrication techniques are regularly employed,
including, e.g., silica based substrates, such as glass, quartz,
silicon or polysilicon, as well as other substrate materials, such
as gallium arsenide and the like. In the case of semiconductive
materials, it will often be desirable to provide an insulating
coating or layer, e.g., silicon oxide, over the substrate material,
and particularly in those applications where electric fields are to
be applied to the device or its contents.
[0020] In additional preferred aspects, the substrate materials
will comprise polymeric materials, e.g., plastics, such as
polymethylmethacrylate (PMMA), polycarbonate,
polytetrafluoroethylene (TEFLON.TM.), polyvinylchloride (PVC),
polydimethylsiloxane (PDMS), polysulfone, polystyrene,
polymethylpentene, polypropylene, polyethylene, polyvinylidine
fluoride, ABS (acrylonitrile-butadiene-styrene copolymer), and the
like. Such polymeric substrates are readily manufactured using
available microfabrication techniques, as described above, or from
microfabricated masters, using well known molding techniques, such
as injection molding, embossing or stamping, by polymerizing the
polymeric precursor material within the mold (See U.S. Pat. No.
5,512,131), or by laser ablation techniques. Such polymeric
substrate materials are preferred for their ease of manufacture,
low cost and disposability, as well as their general inertness to
most extreme reaction conditions. Again, these polymeric materials
may include treated surfaces, e.g., derivatized or coated surfaces,
to enhance their utility in the microfluidic system, e.g., provide
enhanced fluid direction, e.g., as described in U.S. Pat. No.
5,885,470 which is incorporated herein by reference in its entirety
for all purposes.
[0021] The channels and/or chambers of the microfluidic devices are
typically fabricated into the upper surface of the bottom substrate
or portion 12, as microscale grooves or indentations 16, using the
above described microfabrication techniques. The top portion or
substrate 18 also comprises a first planar surface 20, and a second
surface 22 opposite the first planar surface 20. In the
microfluidic devices prepared in accordance with the methods
described herein, the top portion also includes a plurality of
apertures, holes or ports 24 disposed therethrough, e.g., from the
first planar surface 20 to the second surface 22 opposite the first
planar surface. The upper substrate is then overlaid and bonded to
the upper surface of the lower substrate, whereby the grooves are
sealed to form channels. The apertures disposed through the upper
substrate then become wells or reservoirs that are in fluid
communication with the termini of the channels in the finished
layered device.
[0022] Movement of materials through the various channels of the
device is generally carried out by any number of a variety of
material transport systems. For example, in some cases, fluids or
other materials are transported through the channels of the device
using controlled electrokinetic transport methods.
[0023] Alternatively, pressure-based fluid transport methods may be
used. In such cases, a pressure differential is created across the
length of the channel segment through which fluid flow is desired,
forcing or drawing the fluid through that channel. Establishing
these pressure differentials may be accomplished by, e.g., applying
positive pressures to the reservoirs at one end of a channel
system, or alternatively, applying a negative pressure to a waste
reservoir. Methods of engineering channel systems to simplify the
application of pressure and/or vacuum is described in, e.g., U.S.
patent application Ser. No. 09/277,367, filed Mar. 26, 1999, and
incorporated herein by reference in its entirety for all purposes.
Alternative pressure-based systems employ integrated pumps and
valves within the body structure of a microfluidic device to drive
fluid movement through the channels of the device in a controlled
fashion. Such integrated pumps and valves are described in, e.g.,
Published International Patent Application No. WO 97/02357. In
still other alternative pressure-based systems, a wicking material
may be employed to draw fluids or other materials through the
channels of the device, by placing the absorbent wicking material
at an outlet port of one or more of the channels of the device. The
wicking material then draws fluid out of the channel thereby
creating a pressure differential to pull fluid through the
channel.
[0024] Because of their extremely small size, as well as their use
in extremely sensitive and accurate analyses, slight variations in
fabrication among different microfluidic devices can have
substantial effects on the operation of those devices. As a result,
it is desirable to ensure the most accurate fabrication methods. In
accordance with the present invention, these methods utilize
improved methods of aligning either the tooling which is used to
fabricate such devices, or additional elements that are to be
attached or otherwise joined with those devices or portions
thereof.
[0025] For example, regardless of whether a microfluidic device
utilizes pressure based material transport or electrokinetic
methods, inconsistencies in manufacturing can lead to
inconsistencies in the flow of material through the channels of the
device. In the typical fabrication of a microfluidic channel
network, e.g., as described above, the upper substrate layer, e.g.,
that incorporating the reservoirs or wells, is overlaid upon the
lower substrate layer, e.g., the layer incorporating the network of
grooves or channels. Positioning of the reservoirs over the
channels or grooves can affect the length of the channels.
Specifically, if the upper layer is shifted to one side, it may
cover or uncover more of the channel. In order to fabricate
efficient, useful systems, tolerances are set for the alignment
process. Similarly, tolerances are set for the fabrication of the
channels and apertures, e.g., tolerances for size and position.
[0026] In the case of the positioning of the layers, potential
variations are illustrated in FIG. 2. In particular, FIG. 2A
illustrates a portion of a device where the reservoirs 200 and 202
in the reservoir bearing substrate, e.g., upper substrate 18 from
FIG. 1, are positioned in an exemplary desirable orientation
relative to the channel bearing substrate, e.g., lower substrate
14. In particular, the reservoirs 200 and 202 are positioned such
that the channels connected to these reservoirs, 210 and 212,
respectively, are of equivalent length before joining with channel
214 at the intersection 216.
[0027] As shown in FIG. 2B, however, shifting of the reservoir
bearing substrate in one direction relative to the channel bearing
substrate, e.g., in the direction of the arrow, dramatically
shortens the effective length of channels, e.g., that portion
defined between the two substrate layers, prior to the intersection
216. While this would likely not substantially affect the ratio of
material from reservoirs 200 and 202 relative to each other in the
example shown, their ratios relative to materials introduced from
other downstream reservoirs could be dramatically affected.
However, such a variation is, in fact, illustrated in FIG. 2C,
which illustrates a further shifting of the reservoir bearing
substrate relative to the other substrate. In this case, channel
210 is substantially shortened relative to channel 212 prior to the
intersection 216. The result is two channels with markedly
different flow characteristics, e.g., resistances (both electrical
and hydrodynamic).
[0028] In both pressure-based and electrokinetic transport, the
rate of movement of material is inversely proportional to the
resistance through the channel, whether that resistance is
electrical resistance or hydrodynamic resistance. Restated, the
longer a channel is, the more energy that is required, either
electrical or pressure, to drive fluids or other materials through
that channel. Conversely, the shorter the channel, the less energy
is required. Thus, in the case of the scenarios illustrated in FIG.
2, it is clear that the amount of energy required to move material
from each of reservoirs 200 and 202 to the intersection 216 at a
given flow rate, would be substantially greater in the network
illustrated in FIG. 2A than for that shown in FIG. 2B. Similarly,
in the scenario illustrated in FIG. 2C, the amount of energy
required to move material from reservoir 202 to the intersection
216 at a particular flow rate would be substantially greater than
that required to move material from reservoir 200 to intersection
216 at the same flow rate. In the case where a single driving force
is used to move fluids through the various channels, e.g., a single
vacuum applied to channel 214, unknown variations in the lengths of
channels 210 and 212 can lead to unknown variations in their
contributed flow rates.
[0029] The present invention addresses the above-described
inconsistencies in manufacture of channel networks. In particular,
in at least a first aspect, the present invention provides
microfluidic devices, which are fabricated from multiple layers.
The first substrate layer typically includes at least a first
planar surface having at least a first microscale groove fabricated
therein. In addition, the surface also typically includes a well or
depression also fabricated therein, such that the groove terminates
at at least one of its ends in the well. The well is configured
such that the aperture provided within the second covering
substrate layer will more easily be positioned entirely over the
well. Specifically, the well is typically provided with
cross-sectional dimensions that are markedly larger than the cross
sectional dimensions of the aperture (or the aperture is
dimensioned smaller than the well), so as to provide a relatively
larger target to hit when assembling the layers. Accordingly, the
aperture in the assembled device will be in complete communication
with the well. By "in complete communication" is meant that the
aperture opening at the interface of the two substrate layers is
entirely included by the well.
[0030] This aspect of the present invention is schematically
illustrated in FIG. 3. In particular, as shown in FIG. 3A, the body
structure of the overall device 300 is again fabricated as an
aggregation of substrate layers 302 and 304, where a series of
grooves 306 is fabricated onto the upper surface 308 of the lower
substrate layer 304, and the reservoirs at the termini of the
channels are fabricated as apertures 310 and 312 disposed through
the upper substrate layer 302. In accordance with the present
invention, however, wells or depressions 320 and 322 are also
fabricated into the upper surface 308 of the lower substrate 304 at
the same time and using the same processes used in fabricating the
grooves that ultimately form the channels. These wells are
typically larger than the apertures 310 and 312 that are provided
through the upper substrate layer 302, so that positioning of those
apertures completely within the boundaries of the wells in the
ultimate aggregate device is facilitated. In particular, slight to
moderate shifting of the upper substrate relative to the lower
substrate will have only a minimal effect on the relevant channel
length and/or resistance through that channel. FIG. 3B illustrates
the invention from a top view. As shown in FIG. 3B, the wells 320
and 322 indicated by the dashed lines are larger than the
apertures/reservoirs 310 and 312 of the assembled device. Also, as
can be appreciated from these figures, moderate shifting of the
apertures 310 and 312, relative to the channel system of the
device, yields substantially no change in the effective length of
the channels from a resistance standpoint.
[0031] Although the wells and apertures are illustrated as being
circular, it will be appreciated that a variety of different shapes
are practicable for each or either of these elements. Of greater
importance than the shape of the aperture and well is that the well
be of larger dimension than the aperture. Typically, the well has a
cross sectional dimension, e.g., diameter, that is at least 2%
larger than the like cross-sectional dimension of the aperture.
Preferably, the cross-section of the well is at least 5% larger,
often at least 10%, and in some cases at least 20% larger than the
like dimension of the aperture. Typically, the well and aperture
will be between about 1 mm and about 10 mm in cross-section, e.g.,
diameter, and preferably, between about 3 mm and about 8 mm.
[0032] As described above, tolerances are typically set for the
size of the apertures in the upper substrate layer, as well as the
position of those apertures. Thus, in certain particularly
preferred aspects, the wells are fabricated to have a radius that
is larger than the preselected radius of the apertures, e.g., the
designated radius before fabrication without consideration of the
tolerance, by at least equivalent to the sum of the tolerances for
the position and radius of the apertures and preferably at least 2
times the sum of the tolerances. Thus, if the position of the
aperture has a tolerance of +/-1 mm in any direction, and the
radius of the aperture has a tolerance of +/-1 mm, the total
tolerance for the aperture is 2 mm, and the well will have a radius
that is at least 2 mm larger than the preselected radius size of
the aperture. Where the radius is preselected to be 5 mm, the well
will then have a radius that is at least 7 mm and preferably, at
least 9 mm. Of course, the precise size of the well is dependent
upon both the size of the aperture and the positional and radius
tolerances for the aperture. These tolerances will typically vary
depending upon the precision that is desired for the ultimately
fabricated device. Typically tolerances for the position of the
aperture will be from about 100 .mu.m to about 2 mm, while the
radius tolerance will typically be from about 10 .mu.m to about 1
mm. Aperture sizes will typically range from about 1 mm to about 1
cm in diameter.
[0033] As noted above, typically the microfluidic devices include a
number of channels which connect a plurality of reservoirs, e.g.,
e.g., one, two, three, five, ten or more different channels which
may or may not intersect one or more of the other channels. As
such, the channels (also termed a channel network) will typically
each terminate in one of a plurality of separate wells, which, in
turn, are in complete communication with a plurality of separate
apertures in the assembled device.
[0034] Fabrication of the wells into the surface of the first or
lower substrate layer is typically carried out using the same
methods as described above for fabricating the channels, and,
typically, is carried out during the same unit operation. By
fabricating these elements in the same process steps, one can
ensure consistency in the relative positions of these elements from
one device to the next.
[0035] As noted above, the devices described herein may employ any
of a variety of different material transport systems for moving
material through the channels of the assembled device. Accordingly,
in some aspects, the devices incorporate elements, which facilitate
interfacing of these transport systems with the device itself. For
example, in devices using electrokinetic transport, e.g., as
described above, it is sometimes desirable to provide the
reservoirs of the assembled devices with electrodes predisposed
within the reservoirs, which electrodes provide the interface
between the channel networks and an electrical controller system.
This electrical interfacing is schematically illustrated in FIG. 5,
discussed in greater detail, below.
[0036] In alternate aspects, a pressure source is provided
connected to one or more reservoirs of the device. As used herein,
a pressure source includes a source of positive or negative
pressure, e.g., pressure or vacuum pumps, a hydrostatic pressure
source, e.g., a fluid column or siphon, a wick placed at one
terminus of the channel network to draw fluid through the device,
and a capillary network, which draws fluid through the channels by
capillary action.
[0037] This aspect of the present invention also has additional
advantages. For example, by providing a maximum footprint or
channel and reservoir layout on the lower substrate, one can more
effectively plan out and condense channel network geometries.
Specifically, because one fabricates that largest effective
dimensions of the channel and reservoir layouts, one can place
additional channels, etc. more closely together without any concern
for whether such channels may be overlapped by a reservoir in the
ultimate device.
[0038] The present invention also addresses other inconsistencies
of the fabrication process through a similar mechanism, namely the
inclusion of alignment facilitating elements in the fabrication
process, such that alignment of a first structural element with a
second structural element is dictated by the fabrication of the
first element. One example where this is particularly useful is in
the fabrication of microfluidic devices that incorporate external
fluidic elements that must be integrated with internal fluidic
elements. One example of such devices is that which includes an
external capillary element for accessing externally stored
samples.
[0039] FIG. 4 is a schematic illustration of a microfluidic device
and integrated pipettor element from a top (Panel A), side (Panel
B) and perspective view (Panel C). As shown, the device 400
includes a main body structure 402 that includes a channel network
disposed in its interior. The channel network includes a main
analysis channel 404, which fluidly connects a sample inlet 406
with waste reservoir 408. Two reagent reservoirs 410 and 412 are
provided in fluid communication with the analysis channel 404 via
channels 414 and 416, respectively. Reagent reservoirs 410 and 412
are paired with buffer/diluent reservoirs 418 and 420,
respectively, which are in communication with channels 414 and 416
via channels 422 and 424, respectively. In order to prevent
electrolytic degradation of reagent and/or buffer materials, each
of reservoirs 408, 410, 412, 416 and 420 is provided in electrical
and/or fluid communication with an electrical access reservoir/salt
bridge channel 428a/b, 430 a/b, 432a/b, 434a/b, and 436a/b,
respectively. The provision of an electrical access reservoir/salt
bridge allows the application of voltages via electrodes for long
periods of time without resulting in substantial degradation of
reagents, buffers or the like. It should be noted that as reservoir
408 is a waste well, it typically does not require a separate
electrical access reservoir/salt bridge, e.g., 428a/b.
[0040] The device also includes a capillary element 438 which
includes an internal capillary channel running its length, the
capillary channel communicating with the analysis channel 404 via
the sample inlet 406. Although shown as being perpendicular to the
main body structure of the device 402, it will be appreciated that
the capillary element can be coplanar with the body structure,
e.g., extending in the same plane as the body structure and
collinear with the analysis channel, e.g., as described in
Published International Application No. WO 98/00705, which is
incorporated herein by reference.
[0041] FIG. 5 is a schematic illustration of a microfluidic device
incorporating an integrated pipettor element, as well as the
overall material transport control and detection system, which
incorporates the microfluidic device. As shown, the system 500
includes a microfluidic device 400, which incorporates an
integrated pipettor/capillary element 438. Each of the electrical
access reservoirs 428a-436a, has a separate electrode 528-536
disposed therein, e.g., contacting the fluid in the reservoirs.
Each of the electrodes 528-536 is operably coupled to an electrical
controller 502 that is capable of delivering multiple different
voltages and/or currents through the various electrodes. Additional
electrode 538, also operably coupled to controller 502, is
positioned so as to be placed in electrical contact with the
material that is to be sampled, e.g., in multiwell plate 540, when
the capillary element 438 is dipped into the material. For example,
electrode 538 may be an electrically conductive coating applied
over capillary 438 and connected to an electrical lead which is
operably coupled to controller 502. Alternatively, electrode 538
may simply include an electrode wire positioned adjacent the
capillary so that it will be immersed in/contacted with the sample
material along with the end of the capillary element 538.
Alternatively, the electrode may be associated with the source of
material, as a conductive coating on the material source well or as
a conductive material from which the source well was fabricated.
Establishing an electric field then simply requires contacting the
electrical lead with the source well material or coating.
Additional materials are sampled from different wells on the
multiwell plate 540, by moving one or more of the plate 540 and/or
device 400 relative to each other prior to immersing the pipettor
438 into a well. Such movement is typically accomplished by placing
one or more of the device 400 or multiwell plate 540 on a
translation stage, e.g., the schematically illustrated x-y-z
translation stage 542.
[0042] In at least one aspect, the capillary element includes at
least one end that is substantially rectangular, so as to easily
mate with a corresponding substantially rectangular opening on the
body structure of the microfluidic device during fabrication of the
overall device. Rectangular capillaries for use as the capillary
element are generally commercially available, e.g., from VitroCom,
Inc. or Mindrum Precision Products, Inc.
[0043] In fabricating these pipettor devices, component alignment
can yield a number of problems in addition to those recited above.
Most notably, fabrication of reservoirs or apertures, and/or
attachment of an external capillary element must be precisely
positioned in order that the channel in the external capillary
element is aligned with the channel(s) in the interior of the
device. For example, in some cases, an external sampling capillary
element is attached to a microfluidic device by drilling a hole
into the body structure of the device, or a layer of the device,
into which the capillary is inserted. Typically, the hole for the
capillary element is disposed in the substrate layer that does not
have the channel fabricated into it. This allows the capillary
element to be completely inserted into the hole without blocking
the channel in the body structure. Of course, this also requires
precise alignment of the hole in one substrate layer with the
channel in the other layer, so that the channel in the capillary
communicates with the channel in the body structure. As such, an
alignment mark is typically fabricated onto the channel bearing
substrate at the same time as the channels, in order to align the
hole with the channel in the opposing substrate.
[0044] Additionally or alternatively, because solid substrates
often incorporate extremely smooth surfaces, it can be difficult to
machine the hole with such precision. Thus, in certain aspects, the
present invention provides that an alignment mark or guide hole is
fabricated into the substrate surface through which a hole is to be
drilled. This alignment mark or guide hole may be fabricated into
the channel bearing substrate, e.g., where the hole is to function
as a reservoir, at the same time that the channel is fabricated
into that surface, and by the same mechanism, e.g., injection
molding, embossing, etching of silica-based substrates, and the
like. Alternatively, it may be fabricated into the opposing
substrate where the hole is to be used as a junction with an
external capillary. The guide hole is fabricated of such dimensions
that any tools used in subsequent fabrication steps, e.g., a drill
or the like, inserted into the guide hole will not wander during
the machining process.
[0045] By fabricating the alignment mark at the same time as the
channel structures, one is assured that this mark is properly
aligned with those structures. A schematic illustration of this
type of alignment facilitating mark is shown in FIG. 6. As shown, a
substrate layer 600 is provided which is to be mated with one or
more additional substrate layers to produce the device that
incorporates the channel network, e.g., as shown in FIG. 4. A
network of grooves, represented by groove 602, is fabricated into
the surface of the substrate 600. As noted above, the grooves may
be fabricated by a number of means depending upon the nature of the
substrate used. For example, polymeric substrates may be injection
molded, hot embossed, laser ablated or the like, while silica-based
substrates, e.g., glass, quartz, silicon or the like, are typically
etched by conventional photolithography and wet chemical etching,
reactive ion etching, or the like.
[0046] The same fabrication steps used to fabricate the network of
grooves are also used to fabricate an alignment or guide mark or
hole 604. As shown, the guide hole is a recessed "X" that is etched
or otherwise fabricated into the surface. Although shown as an "X"
it will be appreciated that a variety of mark shapes and sizes may
be employed for the alignment mark, e.g., circles, squares, or
other polygons. When a drill bit or other tool is inserted into the
alignment mark, the edges of the mark prevent excessive wandering
of that tool during the machining process such that the machining
process is maintained within a predefined region. In the
illustrated example, the diameter of the drill bit or other tool is
illustrated by the dashed line 606, showing that the finished hole
will communicate with the groove 602. This is particularly suited
for fabricating an aperture or reservoir that communicates with the
groove 602. Although the mark is illustrated as being smaller than
the diameter of the drill bit, it will be appreciated that larger
marks may also be used, provided they perform the ultimately
desired function, e.g., allowing communication between the drilled
hole and the channel network, etc. As shown, the alignment mark 604
is also capable of functioning as a pure alignment mark to
facilitate alignment of an overlaying substrate that contains an
aperture. In that case, the aperture dimensions in the overlaying
substrate are indicated by the dashed line 606. In mating the two
substrate layers, the aperture is centered over the alignment mark
604, in order to ensure fluid communication with groove 602.
[0047] In a similar fashion, alternative fabrication strategies can
take advantage of the concepts of the present invention, namely,
the fabrication of alignment structures that can be used in
accurately aligning tooling or other structural components of the
device.
[0048] For example, as noted above, in some cases, a capillary
element that is to be attached to a planar device may be a
rectangular capillary element. In such cases, the attachment site
for the capillary may be fabricated as part of the same fabrication
process used in the channel structures of the device. This is
schematically illustrated in FIG. 7. In particular, an example of a
device similar to that shown in FIG. 4, but including a collinear,
substantially rectangular capillary element, is shown in FIG. 7A.
As shown, the overall device 700 again includes a main body
structure 702, which includes integrated channel network disposed
in its interior. The rectangular capillary element 738 includes a
capillary channel 740 running its length. The capillary element is
attached to the body structure via a rectangular opening 742 in the
body structure 702. Insertion of a rectangular end of the capillary
element 738 into rectangular opening 742 places the capillary
channel 740 into fluid communication with at least one of the
channels in the integrated channel network within the body
structure.
[0049] Because the opening 742 in the body structure is
substantially rectangular, it is more conveniently fabricated than
circular openings. In particular, while circular openings are
typically drilled or air abraded into a body structure, rectangular
openings are more conveniently fabricated by fabricating
rectangular notches in two substrates by, e.g., photolithographic
methods, which substrates are mated to define the body structure of
the device. The two notches are positioned to provide a single
rectangular opening in the side of the body structure. FIG. 7B
illustrates an expanded view of the joining of a rectangular
capillary with a two-layer microfluidic device. As shown, the
device comprises a two-layer body structure including the
above-described notches. As shown, the body structure 702 is made
up of at least first and second planar substrates 702a and 702b,
respectively. The upper surface of the lower substrate 702a
includes grooves fabricated therein, which correspond to the
desired channel structure of the finished device, e.g., groove 704.
The upper substrate 702b is mated and bonded to the upper surface
of the lower substrate 702a (as illustrated by the dashed arrows).
Typically, bonding is carried out by thermal bonding techniques,
which result in a single integrated unit having sealed channels or
conduits running through its interior. The upper substrate also
typically includes a number of holes disposed through it (not
shown), which holes align with and provide access to the channels
of the finished device. The lower and upper substrates also include
notches 742a and 742b, respectively, which are aligned when the two
substrates are mated, to define an opening.
[0050] The existence of notches on both the upper and lower
substrates function as alignment structures in accordance with the
present invention. In particular, a capillary element that is to be
inserted into the opening formed by the notches can function as an
alignment key in aligning the upper and lower substrates.
Specifically, during the process of bonding the upper and lower
substrates together, the capillary element is inserted into the
opening created by the two notches. This capillary element
maintains the relative positions of these substrates throughout the
bonding process. In addition, the final bonded product also
includes the capillary element bonded in place. This may then be
sealed into place using an appropriate adhesive, epoxy or the like.
It will be appreciated that although the capillary element has been
described as functioning as an alignment key, a separate alignment
key optionally may be used. Specifically, notches may be fabricated
into the upper and lower substrates. An alignment key, such as a
shim or "biscuit" may be inserted into the notch in the first
substrate. The second substrate is then mated with the first
substrate such that the alignment key also inserts into the notch
on the second substrate.
[0051] Although these notches could be of any shape, e.g.,
rectangular, hemispherical, trapezoidal, etc., it is generally
easier to fabricate substantially rectangular notches, e.g., using
the same fabrication techniques and steps used in fabricating the
grooves/channels of the device 700, e.g., groove 704. Substantially
rectangular notches produce a substantially rectangular opening
along the edge of the body structure of the device. The notches
generally range in depth depending upon the dimensions of the
rectangular capillary element to be inserted therein. Typically,
however, these notches will range in depth from about 10 .mu.m to
about 50 .mu.m, and will be fabricated to make the transition from
the channel in the capillary element to the channel in the device's
body structure. For example, where a capillary element has a wall
thickness of 15 .mu.m (e.g., minor axis or interior diameter of 15
.mu.m, with wall thickness of 15 .mu.m yielding overall cross
section of 45 .mu.m), the notch 742a on the lower substrate 702a
will typically be approximately 30 .mu.m deep, e.g., allowing for
15 .mu.m wall thickness and a 15 .mu.m deep channel which matches
up with the minor axis of the capillary element, while the notch
742b on the upper substrate 702b will be approximately 15 .mu.m
deep to accommodate the upper wall of the capillary element. The
notches typically extend into the substrate, e.g., away from the
edge, up to about 2 mm, in order to conveniently and fixedly
receive the capillary element.
[0052] A substantially rectangular capillary element 738 is then
inserted and attached to the body structure 702 via the opening (as
shown by the dashed arrow). Typically, attachment of the capillary
element is accomplished using an adhesive, e.g., epoxy, although
other bonding techniques may also be used depending upon the nature
of the materials used, e.g., thermal bonding, solvent welding,
etc.
[0053] Although the capillary element 738 is shown as being
collinear with the main analysis channel 704 of the device 700, it
will be readily apparent that the rectangular capillary element can
be curved or bent out of the plane of the channel network to
provide a more useful sampling capillary. Bent capillaries can be
held in the bent shape, e.g., by applying a rigid bent sheath,
i.e., plastic sheath or a coated sheath of polyimide or Teflon
(polytetrafluoroethylene) or the like, over the capillary element
to hold the capillary in the bent or curved orientation.
Alternatively, a rectangular capillary can extend out of the plane
of the channel network, e.g., perpendicular to the channel network
plane, e.g., as shown in FIG. 4. In particular, rectangular
openings could be readily fabricated into the lower substrate 702a
using well known fabrication techniques, e.g., etching.
[0054] All publications and patent applications are herein
incorporated by reference to the same extent as if each individual
publication or patent application was specifically and individually
indicated to be incorporated by reference. Although the present
invention has been described in some detail by way of illustration
and example for purposes of clarity and understanding, it will be
apparent that certain changes and modifications may be practiced
within the scope of the appended claims.
* * * * *