Controlled fluid transport in microfabricated polymeric substrates

We claim:

1. A microfluidic system, comprising:

a microfluidic device which comprises a body substantially fabricated from a polymeric material, said body having at least first and second intersecting channels disposed therein, interior surfaces of said at least first and second intersecting channels having a zeta potential associated therewith, which zeta potential is capable of supporting an electroosmotic mobility of a fluid in said channels of at least 1.times.10.sup.-5 cm.sup.2 V.sup.-1 s.sup.-1, wherein said fluid is a sodium borate buffer having an ionic strength of between about 1 and about 10 mM, and a pH of from about 7 to about 9, at least one of said at least first and second intersecting channels having at least one cross sectional dimension in the range of from about 0.1 .mu.m to about 500 .mu.m;

at least first, second and third ports disposed at termini of said first channel and at least one terminus of said second channel, whereby said ports are in electrical contact with a fluid in said first and second channels; and

an electrical control system for concomitantly applying a voltage at at least two of said at least first, second and third ports, to selectively direct flow of a fluid in said first and second intersecting channels by electroosmotic flow.

2. The microfluidic system of claim 1, wherein said zeta potential is capable of supporting an electroosmotic mobility of a fluid in said at least first and second intersecting channels of at least 2.times.10.sup.-5 cm.sup.2 V.sup.-1 s.sup.-4, wherein said fluid is from about 1 to about 10 mM sodium borate buffer at a pH of from about 7 to about 9.

3. The microfluidic system of claim 1, wherein said zeta potential is capable of supporting an electroosmotic mobility of a fluid in said at least first and second intersecting channels of at least 5.times.10.sup.-5 cm.sup.2 V.sup.-1 s.sup.-1, wherein said fluid is from about 1 to about 10 mM sodium borate buffer at a pH of from about 7 to about 9.

4. The microfluidic system of claim 1, wherein said zeta potential is capable of supporting an electroosmotic mobility of a fluid in said at least first and second intersecting channels of at least 1.times.10.sup.-5 cm.sup.2 V.sup.-1 s.sup.-4, wherein said fluid is from about 1 to about 10 mM sodium borate buffer at a pH of from about 7 to about 9.

5. The microfluidic system of claim 1, wherein said polymeric body comprises:

a first planar, polymeric substrate, having at least a first surface, said at least first and second intersecting channels being disposed in said surface; and

a second planar substrate overlaying said first planar polymeric substrate, and sealably covering said at least first and second intersecting channels.

6. The microfluidic system of claim 5, wherein said at least first, second and third ports are disposed through said second planar substrate.

7. The microfluidic system of claim 1, wherein said interior surfaces of said at least first and second intersecting channels are treated to provide said interior surfaces with said zeta potential.

8. The microfluidic system of claim 7, wherein said interior surfaces of said at least first and second intersecting channels are treated by associating a charged compound with said interior surfaces.

9. The microfluidic system of claim 8, wherein said polymeric material comprises a fluorocarbon polymer, and said charged compound comprises a fluorinated buffer modifier.

10. The microfluidic system of claim 7, wherein said interior surfaces of said at least first and second intersecting channels are treated by coating said interior surfaces with a coating material having charged functional groups associated therewith, to provide said interior surfaces with said zeta potential.

11. The microfluidic system of claim 1, wherein said electrical control system concomitantly applies a voltage at at least three of said at least first, second and third ports.

12. The microfluidic system of claim 1, wherein said substrate comprises a fourth port disposed therein, whereby each of said first and second intersecting channels has at least two ports in electrical contact therewith.

13. The microfluidic system of claim 1, wherein said substrate further comprises:

a third channel disposed therein, which third channel intersects at least one of said first or second intersecting channels; and

at least a fourth port disposed at a terminus of said third channel.

14. The microfluidic system of claim 1, wherein said polymeric material is selected from polydimethylsiloxane (PDMS), polyurethane, polyvinylchloride (PVC), polystyrene, polysulfone, polycarbonate, polymethylmethacrylate (PMMA), and polytetrafluoroethylene.

15. The microfluidic system of claim 1, wherein said electrical control system comprises a separate electrode placed in electrical contact with each of said at least first, second and third ports, each of said separate electrodes being separately connected to a voltage controller for separately providing and controlling a voltage applied at each of said electrodes.

16. A method of fabricating a microfluidic device, for use with an electroosmotic fluid direction system, comprising:

molding a polymeric material to form a substrate having at least one surface, said at least one surface having at least first and second intersecting channels disposed therein, each of said at least first and second intersecting channels having an interior surface, said interior surface having a zeta potential associated therewith, which zeta potential is capable of supporting an electroosmotic mobility of a fluid in said channels of at least 1.times.10.sup.-5 cm.sup.2 V.sup.-1 s.sup.-1, wherein said fluid is from about 1 mM to about 10 mM sodium borate buffer, at a pH of from about 7 to about 9, at least one of said first and second intersecting channels having at least one cross-sectional dimension in a range of from about 0.1 .mu.m to about 500 .mu.m; and

overlaying a cover layer on said at least one surface, said cover layer enclosing said first and second intersecting channels, and wherein said substrate and said cover layer together comprise at least three ports disposed therein, each of said at least three ports being in fluid communication with first and second termini of said first channel and at least one terminus of said second channel.

17. The method of claim 16, wherein said polymeric material is selected from polydimethylsiloxane (PDMS), polyurethane, polyvinylchloride (PVC), polystyrene, polysulfone, polycarbonate, polymethylmethacrylate (PMMA), and polytetrafluoroethylene (Teflon )polymers.

18. The method of claim 16, wherein said molding step comprises injection molding said polymeric material to form said substrate.

19. The method of claim 16, wherein said molding step comprises embossing said at least one surface of said substrate to form said at least first and second intersecting channels.

20. The method of claim 16, further comprising the step of treating said interior surfaces of said first and second intersecting channels to provide said zeta potential.

21. The method of claim 20, wherein said polymeric material comprises a fluorocarbon polymer, and said step of treating comprises treating said interior surfaces of said at least first and second channels with a fluorinated modifier compound.

22. The method of claim 20, wherein the polymeric material comprises PDMS and said treating step comprises exposing said interior surfaces of said at least first and second inersecting channels to oxygen plasma.

23. The method of claim 16, wherein said step of overlaying said second planar substrate comprises bonding said cover layer to said surface of said substrate.

24. A method of directing movement of a fluid within a microfluidic device, comprising:

providing a microfluidic device substantially fabricated from a polymeric material, which comprises:

at least first and second intersecting channels disposed in said device, each of said first and second intersecting channels having a fluid disposed therein, wherein said at least first and second channels have interior surfaces, said interior surfaces having a zeta potential associated therewith, which zeta potential is capable of supporting an electroosmotic: mobility of a fluid in said channels of at least 1.times.10.sup.-5 cm.sup.2 V.sup.-1 s.sup.-1, wherein said fluid is a sodium borate buffer having an ionic strength of between about 1 and about 10 mM, and a pH of from about 7 to about 9;

at least first, second, third and fourth ports disposed in said substrate, said first and second ports being in fluid communication with said first channel on different sides of the intersection of said first channel with the second channel, and said third and fourth ports being in fluid communication with said second channel on different sides of the intersection of the second channel with the first channel; and

applying a voltage gradient between at least two of said first, second, third and fourth ports to affect movement of said fluid in at least one of said first and second intersecting channels.

25. The method of claim 24, wherein said applying step comprises concomitantly applying a voltage gradient between at least three of said at least first, second, third and fourth ports.

26. The method of claim 24, wherein said applying step comprises concomitantly applying a voltage gradient between at least four of said at least first, second, third and fourth ports.

27. The method of claim 24, wherein the polymeric material is selected from polydimethylsiloxane (PDMS), polyurethane, polyvinylchloride (PVC), polystyrene, polysulfone, polycarbonate, polymethylmethacrylate (PMMA), and polytetrafluoroethylene.

Description Submit all comments and votes

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a regular application of provisional Patent Application No. 60/015,498, filed Apr. 16, 1996, which is hereby incorporated herein by reference in its entirety for all purposes.

BACKGROUND OF THE INVENTION

There has recently been an increasing interest in the application of manufacturing techniques common to the electronics industry, such as photolithography, wet chemical etching, etc., to the microfabrication of fluidic devices for use in obtaining chemical and biochemical information.

The manufacture of fluidic devices in solid substrates, e.g., silicon, glass, etc., was described as early as 1979, with the disclosure of the Stanford Gas Chromatograph (discussed in Manz et al., Avd. in Chromatog. (1993) 33:1-66, citing Terry et al., IEEE Trans. Electron. Devices (1979) ED-26:1880). These fabrication technologies have since been applied to the production of more complex devices for a wider variety of applications.

To date, the most prominent use of this technology has been in the area of capillary electrophoresis (CE). Capillary electrophoresis typically involves the injection of a macromolecule containing sample, e.g., nucleic acids or proteins, into one end of a thin capillary. A potential is then applied along the length of the capillary to electrophoretically draw the materials contained within the sample through the channel. The macromolecules present in the sample then separate from each other based upon differences in their electrophoretic mobility within the capillary. Such differences in electrophoretic mobility typically result from differences in the charge and/or size of a compound. Other factors can also affect the electrophoretic mobility of a given compound, such as interactions between the compound and the capillary walls, interactions with other compounds, conformation of the compound, and the like.

Capillary electrophoresis methods have traditionally employed fused silica capillaries for the performance of these electrophoretic separations. In more recent applications, this fused silica capillary has been replaced by an etched channel in a solid planar substrate, e.g., a glass or silica slide or substrate. A covering layer or substrate provides the last wall of the capillary.

Early discussions of the use of this planar substrate technology for fabrication of such devices are provided in Manz et al., Trends in Anal. Chem. (1990) 10(5):144-149 and Manz et al., Adv. in Chromatog. (1993) 33:1-66, which describe the fabrication of fluidic devices and particularly capillary electrophoresis devices, in silicon and glass substrates.

Although generally concerned with the movement of material in small scale channels, as the name implies, capillary electrophoresis methods employ electrophoresis to affect that material movement, e.g., the movement of charged species when subjected to an electric field. While providing significant improvements in the separation of materials, these capillary electrophoresis methods cannot be used in the direction of bulk materials or fluids within microscale systems. In particular, because electrophoresis is the force which drives the movement of materials in CE systems, species within the material to be moved which have different electrophoretic mobilities will move at different rates. This results in a separation of the constituent elements of the material. While this typically is not a problem in CE applications, where separation is the ultimate goal, where the goal is the bulk transport of fluid borne materials from one location to another, electrophoretic separation of the constituent elements of that material can create numerous problems. Such problems include excessive dilution of materials in order to ensure complete transport of all materials, biasing of a transported material in favor if faster electrophoresing species and against slower or even oppositely electrophoresing species.

While mechanical fluid direction systems have been discussed for moving and directing fluids within microscale devices, e.g., utilizing external pressures or internal microfabricated pumps and valves, these methods generally require the use of costly microfabrication methods, and/or bulky and expensive equipment external to the microfluidic systems. Accordingly, it would generally be desirable to produce a microscale fluidic device that can be easily and cheaply manufactured. The present invention meets these and other needs.

SUMMARY OF THE INVENTION

It is a general object of the invention to provide microfluidic devices for the performance of chemical and biochemical analyses, syntheses and detection. The devices of the invention combine precise fluidic control systems with microfabricated polymeric substrates to provide accurate, low cost, miniaturized analytical devices that have broad applications in the fields of chemistry, biochemistry, biotechnology, molecular biology and numerous other fields.

In a first aspect, the present invention provides a microfluidic system which includes a microfluidic device. The device comprises a body that is substantially fabricated from a polymeric material. The body includes at least two intersecting channels disposed therein, where the interior surfaces of these channels have a surface potential associated therewith, which is capable of supporting sufficient electroosmotic mobility of a fluid disposed within the channels. At least one of the two intersecting channels has at least one cross sectional dimension in the range of from about 0.1 .mu.m to about 500 .mu.m. The device also includes at least first, second and third ports disposed at termini of the first channel and at least one terminus of the second channel, and these ports are in electrical contact with fluid in the channels. The system also includes an electrical control system for concomitantly applying a voltage at the three ports, to selectively direct flow of a fluid within the intersecting channels by electroosmotic flow.

The present invention also provides a method of fabricating microfluidic devices for use with an electroosmotic fluid direction system. The method comprises molding a polymeric material to form a substrate that has at least one surface, and at least first and second intersecting channels disposed in that surface. Each of the at least first and second intersecting channels has an interior surface which has a surface potential associated therewith, which is capable of supporting sufficient electroosmotic flow of a fluid in those channels. Again, at least one of the intersecting channels has at least one cross-sectional dimension in the range of from about 0.1 .mu.m to about 500 .mu.m. A cover layer is overlaid on the surface of the substrate, whereby the cover layer encloses the intersecting channels. Together, the substrate and cover layer will also comprise at least three ports disposed therein, each of the at least three ports being in fluid communication with first and second termini of said first channel and at least one terminus of the second channel.

In a related aspect, the present invention also provides a method for directing movement of a fluid within a microfluidic device. The method comprises providing a microfluidic device having at least first and second intersecting channels disposed therein. Each of the first and second intersecting channels has a fluid disposed therein, wherein the at least first and second channels have interior surfaces having a surface potential associated therewith, which is capable of supporting sufficient electroosmotic mobility of the fluid disposed in those channels. The device also includes at least first, second, third and fourth ports disposed in the substrate, wherein the first and second ports are in fluid communication with the first channel on different sides of the intersection of the first channel with the second channel, and the third and fourth ports are in fluid communication with the second channel on different sides of the intersection of the second channel with the first channel. A voltage gradient is then applied between at least two of the first, second, third and fourth ports to affect movement of said fluid in at least one of the first and second intersecting channels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic illustration of one embodiment of a microfluidic system.

FIG. 2 is a schematic illustration of one embodiment of a microfluidic device of the present invention.

FIG. 3 is a plot illustrating electroosmotic transport of a neutral fluorescent dye past a detector in a microfluidic channel, fabricated in a polymeric substrate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally provides microfluidic devices and systems, as well as methods for using such devices and systems. The devices and systems of the present invention are generally characterized in that they typically include precise fluid direction and control systems, and that they are largely fabricated from polymeric materials. These two characteristics provide the microfluidic devices and systems of the present invention with a number of advantages over previously used materials, such as silica based substrates, semiconductor substrates, e.g., silicon, and the like, including ease of manufacturing, low cost of materials, and inertness to a wide range of potential reaction conditions, including salts, pH and application of electric fields. In addition, these devices and systems also are generally characterized by their inclusion of, or adaptability to precise fluid direction and control elements.

I. Microfluidics, Generally

As noted above, the present invention generally relates to microfluidic devices and systems, which include precise fluid control elements, e.g., fluid transport and direction systems, and which are fabricated from polymeric substrates.

The term "microfluidic device" as used herein, refers to a device or aggregation of devices, which includes a plurality of interconnected channels or chambers, through which materials, and particularly fluid borne materials may be transported to effect one or more preparative or analytical manipulations on those materials. Typically, such channels or chambers will include at least one cross sectional dimension that is in the range of from about 0.1 .mu.m to about 500 .mu.m, and preferably from about 1 .mu.m to about 100 .mu.m. Dimensions may also range from about 5 .mu.m to about 100 .mu.m. Use of dimensions of this order allows the incorporation of a greater number of channels, chambers or sample wells in a smaller area, and utilizes smaller volumes of reagents, samples and other fluids for performing the preparative or analytical manipulation of the sample that is desired.

The microfluidic device may exist alone or may be a part of a microfluidic system which can include: sampling systems for introducing fluids, e.g., samples, reagents, buffers and the like, into the device; detection systems; data storage systems; and control systems, for controlling fluid transport and direction within the device, monitoring and controlling environmental conditions to which the fluids in the device are subjected, e.g., temperature, current and the like. A schematic illustration of one embodiment of such a system is shown in FIG. 1. As shown, the system includes a microfluidic device 100. The device, and particularly the reagent wells or ports of the device are electrically connected to voltage controller 110, which controls fluid transport within the device. An example of a particularly preferred voltage controller is described in, e.g., U.S. patent application No. 08/691,632, filed Aug. 2, 1996, and incorporated herein by reference in its entirety for all purposes. Detection of the output of the device is carried out by detector 120. Both detector 120 and voltage controller 110 are connected to computer 130, which instructs voltage controller in the selective application of varying voltage levels to the various ports of the device 100. The computer also receives and stores detection data from detector 120, and is typically appropriately programmed to perform analysis of those data.

Microfabricated fluidic substrates have been described for the performance of a number of analytical reactions. For example, U.S. Pat. No. 5,498,392 to Wilding and Kricka, describes a mesoscale apparatus which includes microfabricated fluid channels and chambers in a solid substrate for the performance of nucleic acid amplification reactions. Further, U.S. Pat. No. 5,304,487 to Wilding and Kricka also describes a mesoscale device for detecting an analyte in a sample which device includes a cell handling region. The device also includes microfabricated channels and chambers having at least one cross-sectional dimension in the range of from 0.1 .mu.m to about 500 .mu.m. Similar devices are also described in U.S. Pat. Nos. 5,296,375, 5,304,487, 5,427,946, and 5,486,335, also to Wilding and Kricka, for detection of cell motility and fluid characteristics, e.g., flow restriction as a function of analyte concentration. The disclosure of each of these patents is incorporated herein by reference.

III. Polymeric Substrates

Typically, fabrication of fluidic systems having small or even microscale dimensions has drawn on techniques that are widely used in the electronics industry, such as photolithography, wet chemical etching, controlled vapor deposition, laser drilling, and the like. As a result, these microfabricated systems have typically been manufactured from materials that are compatible with these manufacturing techniques, such as silica, silicon, gallium arsenide and the like. While each of these materials is well suited for microfabrication, and many are well suited for inclusion in microfluidic systems, the costs associated with the materials and manufacture of devices utilizing such materials renders that use commercially impractical.

The present invention on the other hand, is characterized in that the devices are substantially fabricated from polymeric materials. By "Polymeric Substrates" or "Polymeric Materials" is generally meant organic, e.g., hydrocarbon based, polymers that are capable of forming rigid or semi-rigid structures or substrates. By "substantially fabricated from polymeric materials" is meant that greater than 50% (w/w) of the materials used to manufacture the microfluidic devices described herein are polymeric materials. For example, while a substrate may be fabricated entirely of a polymeric material, that substrate may also include other non-polymeric elements incorporated therein, including, e.g., electrodes, glass or quartz detection windows, glass cover layers and the like. Typically, the devices of the present invention comprise greater than 60% polymeric materials, preferably greater than 70%, more preferably greater than 80% and often greater than 95% polymeric materials.

Microfabrication of polymeric substrates for use in the devices of the invention may be carried out by a variety of well known methods. In particular, polymeric substrates may be prepared using manufacturing methods that are common in the microfabrication industry, such as injection molding or stamp molding/embossing methods where a polymeric substrate is pressed against an appropriate mold to emboss the surface of the substrate with the appropriate channel structures. Utilizing these methods, large numbers of substrates may be produced using, e.g., rolling presses or stamps, to produce large sheets of substrates. Typically, these methods utilize molds or stamps that are themselves, fabricated using the above-described, or related microfabrication techniques.

Although generally not preferred for the manufacture of polymeric substrates for cost reasons, other microfabrication techniques are also suitable for preparation of polymeric substrates, including, e.g., laser drilling, etching techniques, and photolithographic techniques. Such photolithographic methods generally involve exposing the polymeric substrate through an appropriate photolithographic mask, i.e., representing the desired pattern of channels and chambers, to a degradative level of radiation, e.g., UV light for set periods of time. The exposure then results in degradation of portions of the surface of the substrate resulting in the formation of indentations which correspond to the channels and/or chambers of the device.

Suitable polymeric materials for use in fabricating substrates are generally selected based upon their compatibility with the conditions present in the particular operation to be performed by the device. Such conditions can include extremes of pH, temperature and salt concentration. Additionally, substrate materials are also selected for their inertness to critical components of an analysis or synthesis to be carried out by the device, e.g., proteins, nucleic acids and the like.

Polymeric substrate materials may be rigid, semi-rigid, or non-rigid, opaque, semi-opaque or transparent, depending upon the use for which they are intended. For example, devices which include an optical or visual detection element, e.g., for use in fluorescence based or calorimetric assays, will generally be fabricated, at least in part, from a transparent polymeric material to facilitate that detection. Alternatively, transparent windows of, e.g., glass or quartz, may be incorporated into the device to allow for these detection elements. Additionally, the polymeric materials may have linear or branched backbones, and may be cross-linked or non-cross-linked. Examples of preferred polymeric materials include, e.g., polydimethylsiloxanes (PDMS), polymethylmethacrylate (PMMA), polyurethane, polyvinylchloride (PVC), polystyrene, polysulfone, polycarbonate and the like.

Typically, the polymeric substrates used in the devices of the present invention are fabricated in two or more parts. Specifically, a first planar substrate element is provided having a plurality of grooves and/or wells, corresponding to the fluid channels and/or chamb