Methods and apparatus for manipulating droplets by electrowetting-based techniques

• US 20040058450A1
• Filed: 09/24/2002
• Published: 03/25/2004
• Est. Priority Date: 09/24/2002
• Status: Active Grant

• Current Assignee: Duke University
• Original Assignee: Duke University
• Inventors: Pamula, Vamsee K., Ren, Hong, Paik, Philip Y., Pollack, Michael G., Fair, Richard B.
• Granted Patent: US 7,329,545 B2
• Time in Patent Office: Days
• US Class Current: 436/150
• CPC Class Codes: B01F 33/3021 the components to be mixed being combined in a single independent droplet, e.g. these droplets being divided by a non-miscible fluid or consisting of independent droplets
• CPC Class Codes: B01F 33/3031 using electro-hydrodynamic [EHD] or electro-kinetic [EKI] phenomena to mix or move the fluids
• CPC Class Codes: B01F 33/30351 using hydrophilic/hydrophobic surfaces
• CPC Class Codes: B01J 2219/00479 Means for mixing reactants or products in the reaction vessels
• CPC Class Codes: B01J 2219/00653 the compounds being bound to electrodes embedded in or on the solid supports
• CPC Class Codes: B01L 2300/089 Virtual walls for guiding liquids
• CPC Class Codes: B01L 2300/165 Specific details about hydrophobic, oleophobic surfaces
• CPC Class Codes: B01L 2400/0415 electrical forces, e.g. electrokinetic
• CPC Class Codes: B01L 2400/0427 Electrowetting
• CPC Class Codes: B01L 3/502792 for moving individual droplets on a plate, e.g. by locally altering surface tension
• CPC Class Codes: C40B 60/14 for creating libraries
• CPC Class Codes: G01N 15/14 Optical investigation techniques, e.g. flow cytometry
• CPC Class Codes: G01N 2035/1046 Levitated, suspended drops
• CPC Class Codes: G02B 26/005 based on electrowetting
• CPC Class Codes: Y10T 436/11 Automated chemical analysis
• CPC Class Codes: Y10T 436/113332 with conveyance of sample along a test line in a container or rack
• CPC Class Codes: Y10T 436/117497 with a continuously flowing sample or carrier stream
• CPC Class Codes: Y10T 436/118339 with formation of a segmented stream
• CPC Class Codes: Y10T 436/25 including sample preparation
• CPC Class Codes: Y10T 436/25625 Dilution
• CPC Class Codes: Y10T 436/2575 : Volumetric liquid transfer

Abstract

In a method for sampling a continuous liquid flow, the liquid flow is supplied to a surface along an input flow path. The liquid flow is sampled by forming a sample droplet from a portion of the liquid flow. The sample droplet is moved along an analysis flow path to a processing area of the surface, where the sample droplet is processed. Discrete sample droplets are formed and moved using an electrowetting technique. A binary mixing apparatus and method are also provided. The apparatus comprises an array of electrodes, an electronic controller communicating with the electrodes, a sample droplet supply area communicating with the array, and an additive droplet supply area communicating with the array. The electronic controller alternately energizes and de-energizes selected electrodes to carry out droplet-to-droplet binary mixing operations to obtain one or more droplets having a target mixing ratio.

Claims

1. A method for sampling a continuous liquid flow, comprising the steps of:

(a) supplying a liquid flow to a surface along a first flow path;

(b) sampling the liquid flow by forming a sample droplet from a portion of the liquid flow;

(c) moving the sample droplet along a second flow path to a processing area of the surface; and

(d) processing the sample droplet at the processing area.

2. The method according to claim 1 wherein the surface comprises an array of electrodes, and the liquid flow portion and the sample droplet electrically communicate with a conductive element and selectively communicate with one or more of the electrodes.

3. The method according to claim 2 wherein the conductive element is spaced from the array of electrodes, and the sample droplet during movement is disposed between the array of electrodes and the conductive element.

4. The method according to claim 2 wherein the step of sampling the liquid flow comprises sequentially energizing and de-energizing a selected set of the electrodes of the array, wherein a first one of the selected electrodes is disposed under the liquid flow along the first flow path, a second one of the selected electrodes is adjacent to the first electrode, and a third one of the selected electrodes is adjacent to the second electrode.

5. The method according to claim 4 wherein the step of sampling the liquid flow comprises energizing the first, second and third electrodes to cause the liquid flow portion to spread over the second and third electrodes from the first electrode, and de-energizing the second electrode to cause the sample droplet to form on the third electrode.

6. The method according to claim 4 wherein the second electrode is adjacent to the first flow path, wherein the droplet is formed adjacent to the first flow path.

7. The method according to claim 2 wherein the step of moving the sample droplet along the second flow path comprises sequentially energizing and de-energizing a selected set of the electrodes of the array.

8. The method according to claim 7 wherein the step of sequentially energizing and de-energizing causes the sample droplet to make a turn as the sample droplet is moved along the second flow path.

9. The method according to claim 2 wherein the step of processing the sample droplet comprises sequentially energizing and de-energizing a selected set of the electrodes of the array.

10. The method according to claim 1 wherein the step of moving the sample droplet comprises merging the sample droplet with an additional droplet to form a combined droplet, and moving the combined droplet along the second flow path to the processing area to mix the combined droplet as it moves along the second flow path.

11. The method according to claim 1 wherein the step of processing the sample droplet comprises merging the sample droplet with an additional droplet to produce a combined droplet.

12. The method according to claim 11 wherein the step of merging causes the sample droplet to become diluted.

13. The method according to claim 11 wherein the step of merging causes the sample droplet to react with the additional droplet.

14. The method according to claim 11 comprising the step of linearly oscillating the combined droplet back and forth to mix its contents.

15. The method according to claim 11 comprising the step of moving the combined droplet along a looped path one or more times to mix its contents.

16. The method according to claim 11 wherein the combined droplet is disposed on a two-by-two array of four electrodes of the surface and overlaps each of the four electrodes, and the method comprises the step of mixing the combined droplet by sequentially energizing and de-energizing each of the four electrodes to rotate the combined droplet.

17. The method according to claim 16 wherein a portion of the combined droplet remains substantially stationary at or near an intersecting region of the four electrodes while the combined droplet is rotating.

18. The method according to claim 11 comprising the step of splitting the combined droplet into first and second split droplets.

19. The method according to claim 18 comprising the step of merging the first and second split droplets to mix their contents.

20. The method according to claim 19 comprising the step of oscillating the first and second split droplets to mix their contents prior to merging the first and second split droplets.

21. The method according to claim 11 wherein the processing area comprises a first electrode, a second electrode adjacent to the first electrode, and a third electrode adjacent to the second electrode, and the sample droplet is merged with the additional droplet by moving the sample droplet from the first electrode to the second electrode and moving the additional droplet from the third electrode to the second electrode, whereby the combined droplet is formed on the second electrode.

22. The method according to claim 21 comprising the step of splitting the combined droplet into first and second split droplets by energizing the first, second and third electrodes to cause the combined droplet to spread to the first and third electrodes, and subsequently de-energizing the second electrode, whereby the first split droplet is formed on the first electrode and the second split droplet is formed on the third electrode.

23. The method according to claim 11 wherein the processing area comprises at least two electrodes, the sample droplet is disposed on one of the electrodes and an additional droplet is disposed on the other electrode, and the sample droplet is merged with the additional droplet by moving either the sample droplet or the additional droplet onto the electrode on which the other droplet is disposed.

24. The method according to claim 1 wherein the step of processing the sample droplet comprises analyzing the sample droplet at the processing area.

25. A method for sampling a continuous liquid flow, comprising the steps of:

(a) supplying a liquid flow to a surface along an input flow path;

(b) sampling the liquid flow by forming a first sample droplet and a second sample droplet from a portion of the liquid flow;

(c) moving the first sample droplet along a first transport flow path to a first destination area of the surface;

(d) moving the second sample droplet along a second transport flow path to a second destination area of the surface.

26. The method according to claim 25 wherein the first droplet is moved at a first movement rate and the second droplet is moved at a second movement rate substantially equal to the first movement rate.

27. The method according to claim 25 wherein the first droplet is moved at a first movement rate and the second droplet is moved at a second movement rate different from the first movement rate.

28. The method according to claim 25 comprising the steps of processing the first sample droplet at the first destination area and processing the second sample droplet at the second destination area.

29. The method according to claim 28 wherein the step of processing the first sample droplet comprises combining the first sample droplet with a first additional droplet.

30. The method according to claim 29 wherein the step of processing the second sample droplet comprises combining the second sample droplet with a second additional droplet.

31. The method according to claim 30 wherein the first additional droplet is different in composition from the second additional droplet.

32. The method according to claim 28 wherein the first and second sample droplets are processed substantially simultaneously.

33. The method according to claim 28 wherein the first and second sample droplets are processed at different rates.

34. The method according to claim 25 wherein the first destination area is adapted to perform a first process and the second destination area is adapted to perform a second process different from the first process.

35. The method according to claim 25 wherein the first and second destination areas are the same area.

36. The method according to claim 25 wherein the first and second sample droplets are formed at two different locations along the input flow path.

37. A method for performing microfluidic sampling, comprising the steps of:

(a) providing a substrate comprising an arrangement of first, second and third electrodes, wherein the second electrode is interposed between the first and third electrodes;

(b) causing a fluid input flow stream to flow to the first electrode;

(c) energizing the first, second and third electrodes to cause a portion of the fluid input flow stream to spread across the second and third electrodes; and

(d) de-energizing the second electrode to form a droplet on the third electrode, the droplet being separate from the fluid input flow stream.

38. The method according to claim 37 wherein the fluid input flow stream flows across the substrate along an input direction, and the second and third electrodes are disposed along the input direction.

39. The method according to claim 37 wherein the fluid input flow stream flows across the substrate along an input direction, and the second and third electrodes are disposed along a transport direction different from the input direction.

40. The method according to claim 37 comprising the step of moving the droplet to a processing area of the substrate by sequentially energizing and de-energizing a selected set of additional electrodes.

41. The method according to claim 37 comprising the step of forming a plurality of droplets by repeating steps (c) and (d) a desired number of times.

42. The method according to claim 41 comprising the step of recombining two or more of the droplets on the substrate to form a fluid output flow stream.

43. A method for sampling a continuous liquid flow, comprising the steps of:

(a) supplying a liquid flow to a surface along a first flow path; and

(b) sampling the liquid flow by performing an electrowetting technique to form a sample droplet on the surface, whereby the sample droplet is distinct from the liquid flow and controllable independently of the liquid flow.

44. The method according to claim 43 wherein the electrowetting technique is performed by providing a set of electrodes on the surface, placing at least a portion of the liquid flow in communication with a conductive element and a first one of the electrodes, and selectively activating and de-activating the set of electrodes, whereby the sample droplet is formed on another electrode different from the first electrode.

45. The method according to claim 44 wherein a second one of the electrodes is disposed adjacent to the first electrode and a third one of the electrodes is disposed adjacent to the second electrode, and the electrowetting technique is performed by energizing the first, second and third electrodes to cause the liquid flow portion to spread across the second and third electrodes, and de-energizing the second electrode to cause the sample droplet to form on the third electrode.

46. The method according to claim 43 comprising the step of moving the sample droplet along a second flow path by electrowetting.

47. A method for mixing the contents of a droplet, comprising the steps of:

(a) providing a two-by-two array comprising first, second, third, and fourth electrodes;

(b) placing a multi-component droplet comprising a first composition and a second composition in electrical communication with the first, second, third and fourth electrodes and with a conductive element; and

(c) mixing the first and second compositions of the multi-component droplet by sequentially energizing and de-energizing the first, second, third, and fourth electrodes to cause the multi-component droplet to rotate.

48. The method according to claim 47 comprising the step of forming the multi-component droplet by combining a first droplet comprising the first composition and a second droplet comprising the second composition.

49. The method according to claim 47 wherein a portion of the multi-component droplet remains substantially stationary at or near an intersecting region between the first, second, third, and fourth electrodes while the multi-component droplet rotates.

50. A binary mixing apparatus comprising:

(a) an array of electrodes;

(b) a conducting element positioned in relation to at least one of the electrodes to enable a droplet placed in electrical communication with the at least one electrode to electrically communicate with the conducting element;

(c) an electrode selector for sequentially energizing one or more selected electrodes of the array to move a droplet disposed on the array into contact with another droplet;

(d) a first droplet supply area communicating with the array; and

(e) a second droplet supply area communicating with the array.

51. The apparatus according to claim 50 comprising a substrate comprising the electrode array.

52. The apparatus according to claim 51 wherein the conducting element is spaced from the substrate to define a space between the conducting element and the substrate, and the space is sized to enable a droplet placed in the space to electrically communicate with the conducting element and the at least one electrode of the array.

53. The apparatus according to claim 52 comprising a plate spaced in parallel with the substrate and comprising the conducting element.

54. The apparatus according to claim 52 comprising a filler fluid contained in the space.

55. The apparatus according to claim 50 wherein the electrodes and the conducting element are hydrophobized.

56. The apparatus according to claim 50 comprising a dielectric layer disposed on the electrode array.

57. The apparatus according to claim 50 wherein the electrode selector comprises a processor.

58. A binary mixing apparatus comprising:

(a) first mixing unit comprising;

(i) a first array comprising a plurality of first electrodes;

(ii) a first sample droplet supply area communicating with the first array;

(iii) a first diluent droplet supply area communicating with the first array; and

(iv) a first droplet outlet area communicating with the first array;

(b) a second mixing unit comprising;

(i) a second array comprising a plurality of second electrodes;

(ii) a second sample droplet supply area communicating with the second array;

(iii) a second diluent droplet supply area communicating with the second array; and

(iv) a second droplet outlet area communicating with the second array and with the first mixing unit; and

(c) an electronic controller communicating with the first and second electrodes and adapted for causing selected first and second electrodes to be energized according to programmable computer program instructions executed by the electronic controller.

59. The apparatus according to claim 58 wherein the first array comprises a first substrate area on which the plurality of first electrodes are disposed, and a first conductive element positioned in relation to at least one of the first electrodes to enable a droplet placed in electrical communication with the at least one first electrode to electrically communicate with the first conductive element.

60. The apparatus according to claim 59 comprising a filler fluid contained between the first array and the first conductive element.

61. The apparatus according to claim 59 wherein the first array and the first conductive element are hydrophobized.

62. The apparatus according to claim 59 comprising a dielectric layer disposed on the first array.

63. The apparatus according to claim 59 wherein the second array comprises a second substrate area on which the plurality of second electrodes are disposed, a second conductive element positioned in relation to at least one of the second electrodes to enable a droplet placed in electrical communication with the at least one second electrode to electrically communicate with the second conductive element.

64. The apparatus according to claim 58 comprising a buffer unit communicating with the first diluent droplet supply area and the second droplet outlet area and controlled by the electronic controller.

65. A method for producing a droplet having a desired mixing ratio, comprising the steps of:

(a) providing an array of electrodes;

(b) providing a sample droplet having an initial concentration and a diluent droplet on the array;

(c) merging the sample droplet with the diluent droplet to form a combined droplet by sequentially energizing and de-energizing a selected set of the electrodes; and

(d) mixing the combined droplet to reduce its concentration below the initial concentration of the sample droplet, whereby the reduced concentration of the combined droplet corresponds to an approximate mixing ratio

66. The method according to claim 65 wherein the step of mixing occurs passively as a result of the merging step.

67. The method according to claim 65 wherein the step of mixing comprises actively mixing the combined droplet by subjecting the combined droplet to an electrowetting-based actuation event.

68. The method according to claim 67 wherein the step of mixing comprises sequentially energizing and de-energizing another selected set of electrodes to move the combined droplet along a desired path across the array.

69. The method according to claim 67 wherein the step of mixing comprises sequentially energizing and de-energizing another selected set of electrodes to oscillate the combined droplet back and forth.

70. The method according to claim 67 wherein the step of mixing comprises sequentially energizing and de-energizing another selected set of electrodes to move the combined droplet along a looped path for a desired number of cycles.

71. The method according to claim 67 wherein the step of mixing comprises sequentially energizing and de-energizing a two-by-two sub-array of first, second, third, and fourth electrodes to rotate the combined droplet for a desired number of cycles.

72. The method according to claim 71 wherein a portion of the combined droplet remains substantially stationary at or near an intersecting region between the first, second, third, and fourth electrodes while the combined droplet rotates.

73. The method according to claim 65 comprising the step of repeating the merging and mixing steps for a determined number of times using one or more additional diluent droplets to form one or more new combined droplets until the reduced concentration of the last combined droplet approaches the desired mixing ratio within a desired range of accuracy.

74. The method according to claim 65 comprising the steps of splitting the mixed combined droplet into two mixed droplets, merging at least one of the two mixed droplets with an additional diluent droplet to form a new combined droplet, and mixing the new combined droplet.

75. The method according to claim 65 comprising the step of, after mixing the combined droplet, determining whether the approximate mixing ratio of the combined droplet approaches the desired mixing ratio within the desired range of accuracy.

76. The method according to claim 75 wherein the step of determining comprises measuring a value representative of the reduced concentration of the combined droplet and comparing the measured value to a determined set point value representative of the desired mixing ratio.

77. The method according to claim 75 wherein, if it is determined that the approximate mixing ratio of the combined droplet has not approached the desired mixing ratio within a desired range of accuracy, merging the combined droplet with a new diluent droplet to form a new combined droplet having a concentration more closely approaching the desired mixing ratio.

78. The method according to claim 65 wherein the sample droplet is provided on a first electrode of a first row of the array and the diluent droplet is provided on a second electrode of a second row of the array, and the sample droplet and diluent droplet are merged by energizing an intermediate row electrode disposed between the first and second rows to cause the sample droplet and diluent droplet to form the combined droplet.

79. The method according to 78 comprising the step of splitting the combined droplet by energizing the first electrode, the intermediate row electrode and the second electrode and then de-energizing the intermediate electrode to form two mixed droplets, wherein the two mixed droplets each have the reduced concentration and are respectively formed on the first and second electrodes.

80. The method according to claim 80 comprising the step of merging a first one of the mixed droplets with an additional diluent droplet to form a new combined droplet having a concentration more closely approaching the desired mixing ratio.

81. The method according to claim 80 wherein the first mixed droplet is initially positioned on a first electrode column of the array and the additional diluent droplet is initially positioned on a second electrode column of the array, and the first mixed droplet and the additional diluent droplet are merged by energizing an intermediate column electrode disposed between the first and second electrode columns to move the first mixed droplet or the additional diluent droplet into contact with the other to form a new combined droplet.

82. A method for producing a droplet having a desired mixing ratio, comprising the steps of:

(a) providing an electrode array comprising a plurality of control electrodes;

(b) providing a first droplet having a first composition on a first control electrode of the electrode array;

(c) providing a second droplet having a second composition on a second control electrode of the electrode array;

(d) energizing a third control electrode of the electrode array disposed between the first and second control electrodes to cause the first droplet and the second droplet to merge with each other at the third control electrode, whereby a merged droplet is formed at the third control electrode comprising the first and second compositions; and

(e) actuating the combined droplet to mix the first and second compositions.

83. The method according to claim 82 wherein the step of actuating the combined droplet comprises subjecting the combined droplet to an electrowetting-based event.

84. A method for producing a droplet having a desired final mixing ratio, comprising the steps of:

(a) in a first mixing unit, mixing a first sample droplet with a first diluent droplet to form a first combined droplet having a desired first intermediate mixing ratio;

(b) in a second mixing unit, mixing a second sample droplet with a second diluent droplet to form a second combined droplet having a desired second intermediate mixing ratio;

(c) transporting the second combined droplet to the first mixing unit; and

(d) in the first mixing unit, combining the first combined droplet with the second combined droplet to form a third combined droplet having the desired final mixing ratio.

85. The method according to claim 84 wherein the first, second and third combined droplets are formed by performing electrowetting-based processes.