MICROFLUIDIC FREE INTERFACE DIFFUSION TECHNIQUES

• US 20120046639A1
• Filed: 08/19/2011
• Published: 02/23/2012
• Est. Priority Date: 04/06/2001
• Status: Active Grant

• Current Assignee: California Institute of Technology, Regents of the University of California (University of California)
• Original Assignee: California Institute of Technology, Regents of the University of California (University of California)
• Inventors: Hansen, Carl L., Quake, Stephen R., Berger, James M.
• Granted Patent: US 8,709,152 B2
• Time in Patent Office: Days
• US Class Current: 604/500
• CPC Class Codes: B01F 25/00 Flow mixers; Mixers for falling materials, e.g. solid particles centrifugal mixers B04
• CPC Class Codes: B01F 33/3039 with mixing achieved by diffusion between layers
• CPC Class Codes: B01J 2219/00355 peristaltic
• CPC Class Codes: B01J 2219/00378 Piezoelectric or ink jet dispensers
• CPC Class Codes: B01J 2219/00396 Membrane valves
• CPC Class Codes: B01J 2219/00398 in multiple arrangements
• CPC Class Codes: B01J 2219/00439 using micromirror arrays
• CPC Class Codes: B01J 2219/005 Beads
• CPC Class Codes: B01J 2219/00527 Sheets
• CPC Class Codes: B01J 2219/00605 the compounds being directly bound or immobilised to solid supports
• CPC Class Codes: B01J 2219/0061 The surface being organic
• CPC Class Codes: B01J 2219/00612 the surface being inorganic
• CPC Class Codes: B01J 2219/00619 using hydrophilic or hydrophobic regions
• CPC Class Codes: B01J 2219/00621 by physical means, e.g. trenches, raised areas
• CPC Class Codes: B01J 2219/00635 by reactive plasma treatment
• CPC Class Codes: B01J 2219/00637 by coating it with another layer
• CPC Class Codes: B01J 2219/00659 Two-dimensional arrays
• CPC Class Codes: B01J 2219/00707 separated from the reactor apparatus
• CPC Class Codes: B01J 2219/00722 Nucleotides
• CPC Class Codes: B01J 2219/00725 Peptides
• CPC Class Codes: B01L 2200/025 : Align devices or objects to ensure defined positions relative to each other
• CPC Class Codes: B01L 2200/027 : for microfluidic devices
• CPC Class Codes: B01L 2200/0605 : Metering of fluids
• CPC Class Codes: B01L 2200/10 : Integrating sample preparation and analysis in single entity, e.g. lab-on-a-chip concept
• CPC Class Codes: B01L 2300/0681 : Filter
• CPC Class Codes: B01L 2300/0861 : Configuration of multiple channels and/or chambers in a single devices
• CPC Class Codes: B01L 2300/123 : Flexible; Elastomeric
• CPC Class Codes: B01L 2300/14 : Means for pressure control
• CPC Class Codes: B01L 2300/18 : Means for temperature control
• CPC Class Codes: B01L 2400/0481 : squeezing of channels or chambers
• CPC Class Codes: B01L 2400/0655 : pinch valves
• CPC Class Codes: B01L 2400/0688 : surface tension valves, capillary stop, capillary break
• CPC Class Codes: B01L 3/502738 : characterised by integrated valves microvalves F16K99/0001
• CPC Class Codes: B01L 3/502746 : characterised by the means for controlling flow resistance, e.g. flow controllers, baffles B01L3/502738 takes precedence
• CPC Class Codes: B01L 3/502769 : characterised by multiphase flow arrangements
• CPC Class Codes: B01L 7/54 : using spatial temperature gradients
• CPC Class Codes: B01L 9/527 : for microfluidic devices, e.g. used for lab-on-a-chip
• CPC Class Codes: B81B 1/00 : Devices without movable or flexible elements, e.g. microcapillary devices
• CPC Class Codes: C30B 29/02 : Elements
• CPC Class Codes: C30B 7/14 : the crystallising materials being formed by chemical reactions in the solution
• CPC Class Codes: F04B 43/043 : Micropumps
• CPC Class Codes: F04B 43/14 : having plate-like flexible members
• CPC Class Codes: F16K 2099/0074 : using photolithography, e.g. etching
• CPC Class Codes: F16K 2099/0078 : using moulding or stamping
• CPC Class Codes: F16K 2099/008 : Multi-layer fabrications
• CPC Class Codes: F16K 2099/0084 : Chemistry or biology, e.g. "lab-on-a-chip" technology
• CPC Class Codes: F16K 2099/0086 : Medical applications
• CPC Class Codes: F16K 99/0001 : Microvalves microdevices B81B1/00; manufacture or treatment of devices or systems in or on a substrate B81C1/00; microfluidic structures B01L3/5027; micropumps F04B19/006
• CPC Class Codes: F16K 99/0015 : Diaphragm or membrane valves
• CPC Class Codes: F16K 99/0017 : Capillary or surface tension valves, e.g. using electro-wetting or electro-capillarity effects
• CPC Class Codes: F16K 99/0059 : actuated by a pilot fluid
• CPC Class Codes: Y10T 117/1004 : with means for measuring, testing, or sensing
• CPC Class Codes: Y10T 117/1008 : with responsive control means
• CPC Class Codes: Y10T 117/1012 : with a window or port for visual observation or examination
• CPC Class Codes: Y10T 137/0318 : Processes
• CPC Class Codes: Y10T 137/0324 : With control of flow by a condition or characteristic of a fluid
• CPC Class Codes: Y10T 137/2224 : Structure of body of device
• CPC Class Codes: Y10T 436/25 : including sample preparation

Abstract

A static fluid and a second fluid are placed into contact along a microfluidic free interface and allowed to mix by diffusion without convective flow across the interface. In accordance with one embodiment of the present invention, the fluids are static and initially positioned on either side of a closed valve structure in a microfluidic channel having a width that is tightly constrained in at least one dimension. The valve is then opened, and no-slip layers at the sides of the microfluidic channel suppress convective mixing between the two fluids along the resulting interface. Applications for microfluidic free interfaces in accordance with embodiments of the present invention include, but are not limited to, protein crystallization studies, protein solubility studies, determination of properties of fluidics systems, and a variety of biological assays such as diffusive immunoassays, substrate turnover assays, and competitive binding assays.

Claims

1. A method of mixing two fluids comprising:

disposing a first static fluid;

disposing a second fluid proximate to the first static fluid to form a fluidic interface;

suppressing convective flow of the first and second fluids such that mixing between the first and second fluids across the interface occurs substantially exclusively by diffusion.

2. The method of claim 1 wherein suppressing convective flow of the first and second fluids comprises restricting in a first dimension a portion of the first and second fluids at the interface.

3. The method of claim 2 wherein the first dimension comprises a width of a microfluidic channel.

4. The method of claim 3 wherein convective flow is restricted due to non-slip layers present at the walls of the channel.

5. The method of claim 1 wherein the second fluid is disposed in direct contact with the first fluid.

6. The method of claim 5 wherein the first fluid is disposed within a branch of the flow channel.

7. The method of claim 6 wherein the first fluid remains static within the branch channel due to a counter pressure.

8. The method of claim 6 wherein the branch channel is dead-ended.

9. The method of claim 1 wherein:

the first fluid is disposed in contact with one side of an obstruction;

the second fluid is disposed in contact with an opposite side of the obstruction; and

the obstruction is removed from the channel to form the fluidic interface.

10. The method of claim 9 wherein:

the first and second fluid are disposed in a microfluidic channel;

the obstruction comprises an elastomer membrane present within the microfluidic channel; and

the elastomer membrane portion is removed by being deflected from the channel in response to an actuation force.

11. The method of claim 10 wherein the width of the microfluidic flow channel is defined by a width of a raised feature of a mold utilized to fabricate the microfluidic flow channel in an elastomer material.

12. The method of claim 11 wherein the width of the raised feature is defined utilizing photolithographic techniques.

13. The method of claim 11 wherein the width of the raised feature is defined by patterning a mask over a region in which the line is to be located, and then removing material on either side of the mask.

14. The method of claim 10 wherein the width of the microfluidic flow channel is defined by a width of a line of sacrificial material encapsulated within a layer of elastomer material.

15. The method of claim 14 wherein the width of the sacrificial material is defined by forming a layer of the sacrificial material over the elastomer and removing sacrificial material from either side of the line.

16. The method of claim 2 wherein the first dimension comprises a width of a hydrophilic path.

17. The method of claim 16 wherein the width of the hydrophilic path is defined by a width of an area of a substrate surface exposed during deposition of hydrophilic material.

18. The method of claim 16 wherein the width of the hydrophilic path is defined by a width of an area of a hydrophilic substrate surface masked during deposition of hydrophobic material.

19. A method of mixing two fluids comprising:

providing a first static fluid having a total volume;

providing a second static fluid having a total volume;

disposing a portion of the first static fluid in contact with a portion of the second static fluid to form a fluidic interface, such that a minimum volume of the first and second fluids is exposed to a steepest concentration gradient present immediately along the fluidic interface.

20. The method of claim 19 wherein portions of the first and second fluids along the interface are restricted by a dimension of a microfluidic flow channel.

21. The method of claim 20 wherein the first fluid is positioned in a first chamber, the second fluid is positioned in a second chamber, and the microfluidic flow channel connects the chambers, such that a ratio of a cross-sectional area of the first chamber to a cross-sectional area of the microfluidic flow channel is between 500 and 25,000.

22. A method of determining a property of a fluidic system comprising:

disposing a first static fluid containing a target;

disposing a second static fluid proximate to the first fluid to form a fluidic interface;

suppressing convective flow of the first and second fluids such that mixing occurs across the interface solely by diffusion to reveal the physical property.

23. The method of claim 22 wherein the first and second fluids are the same and a coefficient of diffusion of the target in another fluid is known, such that a viscosity of the first and second fluids can be determined.

24. The method of claim 22 wherein the second fluid contains an analyte known to bind to the target, such that a concentration of the target can be determined from deviation in an observed diffusive behavior of the analyte from an expected diffusive behavior of the analyte in the absence of the target.

25. The method of claim 24 wherein an affinity of the analyte to the target is known, and a concentration of the target can be determined by deviation of at least one of a temporal diffusion profile and a spatial diffusion profile of the analyte from a corresponding profile expected in the absence of the target.

26. The method of claim 24 wherein an affinity of the analyte to the target is known, and a size of the target can be determined by deviation of at least one of a temporal diffusion profile and a spatial diffusion profile of the analyte from a corresponding profile expected in the absence of the target.

27. The method of claim 24 wherein a relative concentration of the analyte and target is known, and an affinity of the analyte to the target can be determined by deviation of at least one of a temporal diffusion profile and a spatial diffusion profile of the analyte from a corresponding profile expected in the absence of the target.

28. The method of claim 22 wherein the second fluid contains a microorganism, such that chemotaxis exhibited by the organism toward the target can be analyzed.

29. A structure for analyzing a property of a target material comprising:

a first microfabricated region configured to contain a volume of a first static fluid including a target;

a second microfabricated region configured to contain a volume of a second static fluid including an analyte known to bind to the target;

a valve actuable to place the volume of the first fluid in diffusive communication with the volume of the second fluid across a free microfluidic interface; and

a detector configured to detect a presence of the analyte in the first microfabricated region.

30. The structure of claim 29 wherein:

the first microfabricated region comprises a first chamber in fluid communication with a first channel portion restricted in at least one dimension relative to dimensions of the first chamber;

the second microfabricated region comprises a second chamber in fluid communication with a second channel portion restricted in at least one dimension relative to dimensions of the second chamber;

the valve comprises an elastomer membrane deflectable into the channel between the first channel portion and the second channel portion; and

the detector is configured to detect a rate of increase of the concentration of the analyte in the first chamber over time.

31. The structure of claim 29 wherein:

the first microfabricated region comprises a first microfabricated channel portion restricted in at least one dimension;

the second microfabricated region comprises a second microfabricated channel portion restricted in the at least one dimension;

the valve comprises an elastomer membrane deflectable into the microfabricated channel between the first channel portion and the second channel portion; and

the detector is configured to detect a concentration of the analyte over a distance from the valve in the first chamber.

32. The structure of claim 29 wherein the detector is configured to detect at least one of fluorescence, refractive index, colorimetry, surface plasmon resonance, and conductivity.

33. A method of reducing a concentration of a small molecule in a protein sample, the method comprising:

disposing a first static fluid containing the protein sample in a microfluidic channel;

disposing a second static fluid having a low concentration of the small molecule proximate to the first fluid to form a fluidic interface;

suppressing convective flow of the first and second fluids such that the small molecule from the first static fluid diffuses across the interface solely by diffusion to reduce the concentration of small molecule present in the first static fluid.

34. A method of determining reaction between a ligand and a target comprising:

positioning a first fluid containing the ligand in a first chamber;

positioning a second fluid containing the target in a second chamber;

establishing a microfluidic free interface between the first and second fluids in a channel connecting the first and the second chamber;

allowing mixing to occur by diffusion across the microfluidic free interface between the first and second fluids, such that the ligand binds to the target and reactivity between the ligand and target can be determined by deviation of at least one of a temporal diffusion profile and a spatial diffusion profile from a corresponding profile expected in the absence of the target.

35. The method of claim 34 wherein the deviation in diffusion profile reflects a diminished diffusion of a ligand/target combination relative to diffusion of the ligand alone.

36. The method of claim 34 wherein:

the target is bound to an original ligand;

the ligand represents a competitor ligand; and

the deviation in diffusion profile reflects an enhanced diffusion of the displaced original ligand, and is evidenced by a detectable physical property of the original ligand.

37. The method of claim 34 wherein the deviation in diffusion profile is evidenced by emission of a fluorescent signal from the displaced original ligand.

38. The method of claim 34 wherein the deviation in diffusion profile is evidenced by quenching of a fluorescent signal from the displaced original ligand.

39. The method of sampling a chemical reaction under a spectrum of conditions, the method comprising:

forming a microfluidic free interface between a first fluid containing a first reactant and a second fluid containing a second reactant;

causing diffusion of the first reactant into the second fluid to create a concentration gradient of the first reactant; and

observing reaction between the first reactant at various concentrations along the gradient and the second reactant.

40. The method of claim of claim 39 wherein:

the second reactant comprises an enzyme catalyzing a reaction to produce a detectable product; and

the first reactant comprises an inhibitor to the enzyme.

41. The method of claim 41 wherein the product is detected by monitoring at least one of fluorescence, refractive index, colorimetry, surface plasmon resonance, and conductivity.

42. A method of creating a concentration gradient of a chemical species comprising:

disposing a first fluid containing the chemical species;

disposing a second static fluid proximate to the first static fluid to form a microfluidic free interface;

suppressing convective flow of the first and second fluids such that mixing between the first and second fluids across the microfluidic free interface occurs substantially exclusively by diffusion and a concentration gradient of the chemical species is created.

43. The method of claim 42 wherein the first chemical species comprises a nutrient for a cell in fluidic communication with the second fluid.

44. The method of claim 42 further comprising:

disposing a third fluid containing a second chemical species proximate to the second fluid to form a second microfluidic free interface;

suppressing convective flow of the second and third fluids such that mixing between the second and third fluids across the second microfluidic free interface occurs substantially exclusively by diffusion and a second concentration gradient of the second chemical species is superimposed over the concentration gradient of the first chemical species.

45. The method of claim 44 wherein a direction of the concentration gradient of the first chemical species is not parallel with a direction of the concentration gradient of the second chemical species.

46. The method of claim 44 wherein the direction of the concentration gradient of the first chemical is approximately perpendicular to a direction of the concentration gradient of the second chemical, such that an array of concentration conditions of the first and second chemical species is created.

47. The method of claim 46 wherein diffusion of the first and second chemical species occurs in a shallow chamber.

48. The method of claim 46 wherein diffusion of the first and second chemical species occurs in a set of orthogonally-oriented microfluidic flow channels.

49. A method of introducing a drug into a subject comprising:

disposing a first static fluid containing the drug in a microfluidic device;

disposing a second fluid in the microfluidic device between the first static fluid and the subject;

establishing a microfluidic free interface between the first fluid and the second fluid, such that a predetermined amount of the drug diffuses to reach the subject only after a predetermined time.

50. The method of claim 49 wherein a time of diffusion of the drug to the subject is determined by a dimension of a channel in the microfluidic device positioned between the subject and the first fluid.

51. A method of controlling the concentration of reactants during a chemical reaction comprising:

disposing a first static fluid containing a first reactant in a microfluidic structure;

disposing a second fluid in the microfluidic structure proximate to the first static fluid, the second static fluid containing a second reactant;

establishing a microfluidic free interface between the first and second fluids;

allowing diffusion between the first and second fluids across the microfluidic free interface to determine the relative concentration of the first and second reactants.