Microfluidic chip having integrated electrodes

A microfluidic device having integrated components for conducting chemical operations. Depending upon the desired application, the components include electrodes for manipulating charged entities, heaters, electrochemical detectors, sensors for temperature, pH, fluid flow, and other useful components. The device may be fabricated from a plastic substrate such as, for example, a substantially saturated norbornene based polymer. The components are integrated into the device by adhering an electrically conductive film to the substrate. The film may be made of metal or an electrically conducting ink and is applied to the device through metal deposition, printing, or other methods for applying films. Methods for reducing bubble formation during electrokinetic separation and methods for heating material in a microfluidic device are also disclosed.

 

1. A microfluidic device for operations at high field strengths comprising:

a substrate having at least one channel and at least one aperture in fluid communication with said channel;

a cover bonded to said substrate such that a reservoir is formed at said at least one aperture; and

a driving electrode used to apply a field of at least 400 V/cm comprised of an electrically conducting silver/silver chloride ink pattern on at least one of said substrate and cover such that when a material is present in said channel and reservoir said ink pattern makes electrical contact with said material and such that fewer bubbles form in said channel and reservoir when establishing said field across a driving electrode of bare platinum.

2. The device of claim 1 wherein said ink pattern is on said cover.

3. The device of claim 1 wherein said electrical contact is made in said reservoir.

4. The device of claim 1 comprising a first channel, a second channel, and a third channel, the first and second channel being fluidly connected to the third channel at separate points along the third channel and wherein said electrical contact is made in one of the first channel, second channel, and third channel.

5. The device of claim 1 wherein said cover is bonded to said substrate by one method selected from the group consisting of thermal bonding, using an adhesive and using a double-sided adhesive layer.

6. The device of claim 1 wherein said material is a substance useful in electrophoretic applications.

7. The device of claim 1 wherein said ink pattern is on said substrate.

8. The device of claim 1 wherein said ink is patterned on said cover using one method selected from the group consisting of ink jet printing, screen printing and lithography.

9. The device of claim 1 wherein said cover is made of PMMA.

10. The device of claim 1 wherein said ink is an acrylic-based silver/silver chloride ink.

11. The device of claim 1 wherein said ink is a polyester based silver/silver chloride ink.

12. The device of claim 1 wherein said ink pattern has width of 10 to 400 μm.

13. The device of claim 1 wherein said ink pattern includes a contact and a lead.

14. The device of claim 1 wherein said substrate is made from a plastic selected from the group consisting of norbornene, polystyrene, acrylic, polycarbonate-polyester, and polyolefin.

15. The device of claim 1 wherein said substrate is a norbornene based substrate.

16. A method for reducing bubble formation during electrokinetic applications in a microfluidic device having interconnected channels and reservoirs, said method comprising the steps of:

providing at least two driving electrodes for contacting a medium in said channels and reservoirs when the medium is present, wherein at least one driving electrode has a surface comprising silver and silver chloride; and

establishing a field of at least 400 V/cm across the at least one driving electrode having a surface comprising silver and silver chloride and another driving electrode such that fewer bubbles form in said channels and reservoirs as are formed when establishing said field across driving electrodes of bare platinum.

17. The method of claim 16 wherein said microfluidic device comprises a substrate and a cover bonded to said substrate and wherein said electrodes are integrated electrodes formed using an ink patterned on said cover such that when said cover is bonded to said substrate to form said device said ink is positioned in said reservoir and makes electrical contact with said medium therein.

18. The method of claim 16 wherein at least one of said electrodes is positioned in one of said reservoirs to make electrical contact with said medium in said reservoirs and wherein said electrode comprises a silver/silver chloride coated electrode.

19. The method of claim 17 wherein the ink is an acrylic-based silver/silver chloride ink.

20. The method of claim 17 wherein the ink comprises a polyester-based silver/silver chloride ink.

TECHNICAL FIELD

This invention relates to microfluidic chips and in particular, to microfluidic chips having integrated electrodes.

BACKGROUND

Miniaturized devices for conducting chemical and biochemical operations have gained widespread acceptance as a new standard for analytical and research purposes. Provided in a variety of sizes, shapes, and configurations, the efficiency of these devices has validated their use in numerous applications. For example, microfluidic lab chips are utilized as tools for conducting capillary electrophoresis and other chemical and biochemical analysis in a reproducible and effective manner. Microarrays or Bio-chips are used to conduct hybridization assays for sequencing and other nucleic acid analysis.

In a typical labchip, materials are electrokinetically driven through interconnected microchannels. Electrodes are positioned in reservoirs fluidly connected to the microchannels to make electrical contact with a medium contained therein. Application of a voltage across two electrodes will drive material from one reservoir to another based on electrokinetic transport phenomena. In a microfluidic device having numerous channels and reservoirs to perform multiplexed procedures, an electrode array (e.g., 10 to 100 or more electrodes) may be positioned such that each electrode makes electrical contact with the medium in the device. Programmable controllers may be electrically connected to the electrodes to individually drive the electrodes in a controlled manner. Examples of the use of voltages and electrodes to transport materials electrokinetically are disclosed in, for example, U.S. Pat. Nos. 5,126,022; 5,750,015; 5,858,187; 6,010,607; and 6,033,546.

Various problems arise, however, when electrodes are "dropped in" reservoirs on a chip. First, the electrodes are subject to contamination from previous testing. An electrode dropped into one test chip may introduce unwanted material into a device subsequently tested, thereby contaminating the subsequently tested chip.

Additionally, when conventional metal electrodes (i.e. platinum, gold, etc.) are used to apply electrical fields within certain conductive media such as aqueous conductive media, bubbles are prone to form thereby disrupting the intended operation of the device. This problem is exacerbated in applications such as capillary electrophoresis where higher voltages are desirable to achieve more efficient separations (i.e. higher throughput, better resolution, etc.).

Within an electrophoretic channel or in a reservoir connected thereto, gas bubbles (e.g., an air bubble) can interfere with the electrical connection or otherwise change electrical properties between driving electrodes and the conductive medium. When bubbles are formed, electrokinetic operations can be severely or completely inhibited. Accordingly, current protocols for conducting capillary electrophoresis utilize remedial electrode configurations and are limited to voltages that will not generate substantial bubbles. These conventional protocols, however, typically do not achieve the desirable higher throughput of systems employing relatively higher voltages.

"Dropped in" electrodes must also be carefully aligned and the depth must be controlled. Positioning the electrodes too deep may break the electrode or damage the device; positioning the electrode too shallow may prevent application of a voltage to the medium in the device and thus prevent driving the sample material through the device. Further, moving electrodes into position adds complexity to the instrument used to carry out the testing.

It is therefore desirable to provide a microfluidic device that does interfere with the intended operations of the microdevice yet can still be integrated with electrically conductive components necessary for chemical and biochemical operations, e.g., heating elements, electrodes, electrochemical detectors, valves, flow detectors and the like.

SUMMARY OF THE INVENTION

In one variation of the present invention, a microfluidic chip includes a substrate having interconnected microchannels and at least one aperture. A cover is bonded to the substrate to enclose the microchannels and form a reservoir at the at least one aperture. An electrically conducting ink is patterned on the cover or the substrate such that the electrically conducting ink makes an electrical connection with a medium contained in the microchannels or reservoirs. In a variation, an ink trace is positioned in the reservoirs and can be used to drive materials through the channels by application of a voltage to the ink trace. In another variation, the ink trace is positioned in a channel and is used to heat or detect materials in the channels.

In another variation of the present invention, a method is provided for reducing bubble formation during electrokinetic applications in a microfluidic device having channels and reservoirs. The method includes applying voltage to a medium contained in the channel and reservoirs through an electrically conducting ink. In one variation the electrically conducting ink is a trace patterned on a cover or substrate of the microfluidic device. In another variation, the electrically conducting ink is a coating on an electrode dropped in a reservoir in the device. A platinum wire electrode, for example, may be coated with an electrically conducting ink to reduce bubble formation in this variation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top view of a microfluidic device having integrated electrodes in accordance with the present invention.

FIG. 2 shows a cross sectional view of the device shown in FIG. 1 taken along A—A.

FIGS. 3A-3B show cross sectional views of the device shown in FIG. 1 taken along B—B having various assemblies in accordance with the present invention.

FIG. 3C shows a cross-section of a variation of the present invention wherein a channel is formed due to an adhesion layer overlapping the electrodes.

FIGS. 4A and 4B show a cross sectional view of a microfluidic device having two microchannel systems: one system providing the leads to an electrode and the other system providing for an analytical capillary channel. FIG. 4A shows the unassembled device. FIG. 4B shows the fully assembled device.

FIG. 5 shows a top view of a microanalysis channel in accordance with the present invention that has both an electrochemical detector and a semi-circular driving electrode integrated therein.

FIGS. 6A and 6B show a top view and cross sectional view of a microfluidic device having an integrated electrode heater in accordance with the present invention.

FIGS. 6C and 6D show a top view and cross sectional view of another variation of a microfluidic device having an integrated electrode heater in accordance with the present invention.

FIGS. 7A-7C show cross sectional views of an integrated device in accordance with the present invention having alternative configurations: in particular, the electrode (indicated by reference numeral 301) is shown in a different position relative to the other components in each of FIGS. 7A-7C.

FIG. 8 shows a top view of a microanalysis channel in accordance with the present invention that has both a heater and a driving electrode integrated therein where the driving electrode has a minimized surface area for reducing unwanted hydrolysis or gas generating reactions.

FIG. 9 shows a top view of a heater integrated into a norbornene based substrate. The pattern includes a metal heating element and its incorporated lead.

FIG. 10 shows an electrophoretic separation for P450 assay on conductive ink-integrated chip: the line at the bottom is the control experiment using platinum wire as electrodes and carboxyfluorescein is used the internal reference.

FIG. 11 shows en electrophoretic separation for Kinase assay on conductive ink-integrated chip in accordance with the present invention: the line at the bottom is the control experiment using platinum wire as electrodes and carboxyfluorescein is used as the internal reference.

FIG. 12A shows DNA separation using ink-integrated microchips in accordance with the present invention: the sample is Genescan 700, denatured at 95° C. for 2 minutes and chilled down on ice and the 18 peaks are 75, 100, 139, 150, 160, 200, 250, 300, 340, 350, 400, 450, 490, 500, 550, 600, 650, and 700 base pairs DNA fragment.

FIG. 12B shows DNA separation using platinum wires as driving electrodes (the control experiment): the sample was Genescan 700, denatured at 95° C. for 2 minutes and the 18 peaks are 75, 100, 139, 150, 160, 200, 250, 300, 340, 350, 400, 450, 490, 500, 550, 600, 650, and 700 bp DNA fragment.

FIG. 13 shows an eTag™ probe separation using an electrode-integrated plastic chip in accordance with the present invention.

FIG. 14A shows separation data of 13 eTag™ probes using a carbon ink electrode integrated on a plastic chip in accordance with the present invention. The lower electropherogram is data from a control experiment where platinum wires were used as driving electrodes in the same reservoirs as the integrated electrodes.

FIG. 14B shows separation data of 13 eTag™ probes using an Ag/AgCl ink electrode integrated on a plastic chip in accordance with the present invention. The lower electropherogram is data from a control experiment where platinum wires were used as driving electrodes in the same reservoirs as the integrated electrodes.

FIGS. 15A and 15B show graphical illustrations of cyclic voltammetry data of platinum wire, carbon ink-, 20% Pd doped carbon ink-, Ag/AgCl ink-coated platinum wires in a buffer solution (pH=8.0) using a scan rate of 100 mV/s. The reference electrode is Ag/AgCl and the counter electrode is a platinum wire.

FIG. 16 shows separation of 13 eTag™ probes using carbon-ink-coated platinum wires as driving electrodes in accordance with the present invention.

FIG. 17 shows separation of 13 eTag™ probes using Ag/AgCl-ink-coated platinum wires as driving electrodes in accordance with the present invention.

FIG. 18 shows a cross sectional view of another microfluidic device having an integrated heater in accordance with the present invention.

FIG. 19 shows thermal response as a function of time for an applied voltage of 20 V of an integrated ink electrode heater on a microfluidic chip in accordance with the present invention. The heater features a serpentine shape.

FIG. 20 shows thermal response as a function of time for an applied voltage of 15 V of an integrated ink electrode heater on a microfluidic chip in accordance with the present invention. The heater is a single strip trace of 84.5×1×0.030 mm.

FIGS. 21A and 21B show thermal response as a function of voltage and resistance respectively of an integrated ink electrode heater on a microfluidic device in accordance with the present invention. The heater is a single strip.

FIG. 21C shows thermal cycling of screen printed heaters on plastic chip in accordance with the present invention and a commercial heat strip.

FIGS. 22A and 22B show partial top and cross sectional views respectively of a microfluidic device having an integrated chemical sensor in accordance with the present invention.

FIG. 23 shows data for a separation of 13 eTag probes on a microfluidic device integrated with Ag/AgCl ink electrodes. The field strength was increased from 400 V/cm (bottom) to 600 V/cm (top).

FIG. 24A shows data for a separation of 13 eTag probes on a microfluidic device using platinum wires as external driving electrodes. The field strength was 600 V/cm.

FIG. 24B shows data for a separation of 13 eTag probes on a microfluidic device integrated with carbon ink electrodes. The separation strength is 600 V/cm.

FIG. 24C shows a separation of 13 eTag probes on a microfluidic device integrated with Ag/AgCl ink electrodes. The separation strength is 600 V/cm.

FIG. 25 is a summary chart for the field strength test (600 V/cm) using Ag/AgCl-ink-integrated microfluidic devices.

DETAILED DESCRIPTION

The present invention is directed to an integrated microdevice for conducting chemical operations. By chemical operations, it is meant analytical and research applications that are by nature, chemical, biochemical, electrochemical, biological, and the like.

In one variation of the present invention, a microfluidic chip includes a substrate having interconnected microchannels and at least one aperture. A cover is bonded to the substrate to enclose the microchannels and form a reservoir at the at least one aperture. An electrically conducting ink is patterned on the cover or the substrate such that the electrically conducting ink makes an electrical connection with a medium contained in the microchannels or reservoirs. In other cases, the ink electrode traces are not in direct connection with the medium. In a variation, an ink trace is positioned in the reservoirs and can be used to drive materials through the channels by application of a voltage to the ink trace. In another variation, the ink trace is positioned in a channel and is used to heat or detect materials in the channels.

In another variation of the present invention, a method is provided for reducing bubble formation during electrokinetic applications in a microfluidic device having channels and reservoirs. The method includes applying voltage to a medium contained in channels and reservoirs through an electrically conducting ink. In one variation the electrically conducting ink is a trace patterned on a cover or substrate of the microfluidic device. In another variation, the electrically conducting ink is a coating on an electrode dropped in a reservoir in the device. A platinum wire electrode, for example, may be coated with an electrically conducting ink to reduce bubble formation in this variation.

In yet another variation of the present invention the device employs one or more functional components adhered to a microfluidic device. Functional components, microchannels, microarrays, reservoirs, and apertures (through-holes) may be formed in the substrate or cover or the features may be formed in both the substrate and the cover. The parts may then be bonded together to form the microfluidic device of the present invention. Depending upon the application, by functional components it is intended electrically conductive elements that facilitate or enable the intended chemical operations. For example, functional components can be electrodes for manipulating charged entities, heaters, electrochemical detectors, valves, sensors for temperature, pH, fluid flow, and the like.

Other variations of the above described invention are disclosed hereinafter and other variations will become apparent upon reading the following description in conjunction with the accompanying drawings.

Microfluidic Devices

An example of a microfluidic device or chip 10 in accordance with the present invention is shown in FIGS. 1 and 2. FIG. 1 is a top view of a chip 10 and FIG. 2 is a cross sectional view of the chip 10 of FIG. 1 taken along A—A. The microfluidic device 10 shown in FIGS. 1 and 2 is not to scale and is intended to illustrate structure which may be difficult to recognize if drawn to scale. In particular, the size of microchannel 14 relative to the thickness of the device 10 is exaggerated in FIG. 2.

Microfluidic device 10 includes a substrate 18 and a cover or plate 20 bonded to the substrate. While the substrate 18 is shown in the figures as a rectangular plate, the substrate may take a variety of different shapes including disc-like or other shapes. Further, the substrate is not limited to being positioned on top but may be positioned on the bottom of the microfluidic device or positioned in the microfluidic device between two components as in a sandwich configuration. Examples of microfluidic structures are described in, for example, U.S. Pat. Nos. 5,750,015, 5,126,022 and 6,033,546.

A substrate or chip preferably has a thickness (T), width (W), and length (L) of 0.005 to 0.5 inches, 0.5 to 10 inches and 1 to 10 inches, respectively. Additionally, certain films may be used as chips and be as thin as 0.005 inches.

The substrate 18 typically features at least one generally planar surface having one or more microchannels 14 and one or more apertures or through-holes 24 in fluid communication with the microchannels. Wells or reservoirs 26 are formed at the through-holes 24 when the cover 20 is bonded to the substrate 18 as shown in FIGS. 1 and 2. In one variation, a thin film cover is bonded to the bottom o