Method and apparatus for non-contact electrostatic actuation of droplets

• US 20040055536A1
• 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: Fair, Richard B., Kolar, Pramod
• Granted Patent: US 6,989,234 B2
• Time in Patent Office: Days
• US Class Current: 118/626
• CPC Class Codes: B01J 2219/0036 Nozzles
• CPC Class Codes: B01J 2219/0065 by the use of liquid beads
• CPC Class Codes: B01J 2219/00653 the compounds being bound to electrodes embedded in or on the solid supports
• CPC Class Codes: B01L 2200/0626 using levitated droplets
• CPC Class Codes: B01L 2300/089 Virtual walls for guiding liquids
• CPC Class Codes: B01L 2400/027 electrostatic forces between substrate and tip
• CPC Class Codes: B01L 2400/0415 electrical forces, e.g. electrokinetic
• CPC Class Codes: B01L 2400/0427 Electrowetting
• CPC Class Codes: B01L 3/0241 Drop counters; Drop formers making arrays for combinatorial libraries B01J19/0046; automation of dispensing for analysis G01N35/10
• CPC Class Codes: B05B 5/0255 spraying and depositing by electrostatic forces only
• CPC Class Codes: B41J 2002/14395 Electrowetting
• CPC Class Codes: C40B 60/14 for creating libraries

Abstract

An apparatus for actuating a droplet comprises a first conductive layer, a second conductive layer, a conductive elongate element, and a voltage source. The first conductive layer comprises a first hydrophobic surface. The second conductive layer comprises a hydrophilic surface facing the first hydrophobic surface. The second conductive layer is axially spaced from the first conductive layer to define a gap therebetween. The conductive medial element is disposed in the gap between the first and second conductive layers, and comprises a second hydrophobic surface. The voltage source communicates with the second conductive layer and the elongate element. By applying a voltage potential between the elongate element and the second conductive layer, droplets can be electrostatically actuated so as to move from the first conductive layer into contact with the second conductive layer. The apparatus is particularly useful in the synthesis of microarrays of biological, chemical, or biochemical samples.

Claims

1. An apparatus for actuating a droplet, comprising:

(a) a first conductive layer comprising a first hydrophobic surface;

(b) a second conductive layer comprising a hydrophilic surface facing the first hydrophobic surface, the second conductive layer axially spaced from the first conductive layer to define a gap therebetween;

(c) a conductive elongate element disposed in the gap between the first and second conductive layers and comprising a second hydrophobic surface; and

(d) a voltage source communicating with the second conductive layer and the elongate element.

2. The apparatus according to claim 1 wherein the first conductive layer comprises a plurality of control electrodes covered by the first hydrophobic surface.

3. The apparatus according to claim 2 comprising a second voltage source communicating with the control electrodes and the elongate element.

4. The apparatus according to claim 1 wherein the first conductive layer comprises a planar body, and the first hydrophobic surface is disposed on the planar body.

5. The apparatus according to claim 4 wherein the planar body comprises a glass.

6. The apparatus according to claim 4 wherein the first conductive layer comprises a conductive material disposed on the planar body, and the first hydrophobic surface is disposed on the conductive material.

7. The apparatus according to claim 6 wherein the conductive material comprises a metal.

8. The apparatus according to claim 6 wherein the conductive material comprises indium tin oxide.

9. The apparatus according to claim 6 wherein the first conductive layer comprises a dielectric material disposed on the conductive material, and the first hydrophobic surface is disposed on the dielectric material.

10. The apparatus according to claim 9 wherein the dielectric material comprises a parylene composition.

11. The apparatus according to claim 1 wherein the first hydrophobic surface comprises a hydrophobized region of the first conductive layer.

12. The apparatus according to claim 1 wherein the first hydrophobic surface comprises a hydrophobic layer disposed on the first conductive layer.

13. The apparatus according to claim 12 wherein the hydrophobic layer comprises PTFE.

14. The apparatus according to claim 1 wherein second conductive layer comprises a planar body, the planar body comprises an outer surface opposing the hydrophilic surface, and a conductive backing is disposed on the outer surface.

15. The apparatus according to claim 14 wherein the planar body comprises a derivatized glass.

16. The apparatus according to claim 14 wherein the conductive backing comprises a metal.

17. The apparatus according to claim 14 wherein the conductive backing comprises indium tin oxide.

18. The apparatus according to claim 1 wherein the hydrophilic surface of the second conductive layer comprises a plurality of analyte-specific receptor sites.

19. The apparatus according to claim 18 wherein the first conductive layer comprises a plurality of control electrodes, and at least one of the control electrodes is aligned across the gap with a corresponding group of the receptor sites.

20. The apparatus according to claim 1 wherein the second hydrophobic surface comprises a hydrophobized region of the elongate element.

21. The apparatus according to claim 1 wherein the second hydrophobic surface comprises a hydrophobic layer disposed on the elongate element.

22. The apparatus according to claim 21 wherein the hydrophobic layer comprises PTFE.

23. The apparatus according to claim 1 wherein the elongate element comprises a metal-containing wire.

24. The apparatus according to claim 1 comprising a plurality of conductive elongate elements disposed in the gap.

25. The apparatus according to claim 1 comprising a spacer element, wherein the elongate element is supported by the spacer element.

26. The apparatus according to claim 1 comprising a container, wherein the first conductive layer, the second conductive layer, and the elongate element are disposed in the container.

27. The apparatus according to claim 26 comprising a filler fluid disposed in the gap between the first and second conductive layers.

28. The apparatus according to claim 1 comprising an electronic controller communicating with the voltage source.

29. The apparatus according to claim 1 wherein the elongate element is spaced from the first conductive layer at a distance of approximately 0.05 mm to approximately 2 mm.

30. A method for electrostatically actuating a droplet, comprising the steps of:

(a) placing a droplet on a first conductive layer;

(b) positioning the droplet into alignment with a target site of a second conductive layer axially spaced from the first conductive layer;

(c) grounding the droplet by contacting the droplet with an elongate grounding element axially spaced between the first and second conductive layers; and

(d) actuating the droplet by applying a voltage potential between the grounding element and a second conductive layer axially spaced from the grounding element, whereby the droplet is charged and attracted to the second conductive layer and moves off the first conductive layer into contact with a hydrophilic surface of the second conductive layer.

31. The method according to claim 30 wherein the droplet placed on the first conductive layer comprises a fluid and an analyte.

32. The method according to claim 31 wherein the step of actuating the droplet into contact with the hydrophilic surface of the second conductive layer causes the analyte of the droplet to remain on the hydrophilic surface.

33. The method according to claim 32 wherein the hydrophilic surface comprises analyte-specific receptor sites.

34. The method according to claim 30 wherein the step of positioning the droplet comprises causing the droplet to move across the first conductive layer by performing an electrowetting-based actuation technique.

35. The method according to claim 30 wherein the step of positioning the droplet comprises moving the first conductive layer.

36. The method according to claim 35 wherein the step of actuating the droplet causes the droplet to move around the elongate element.

37. The method according to claim 30 wherein the step of actuating the droplet into contact with the hydrophilic surface of the second conductive layer causes at least a portion of the droplet to remain on the hydrophilic surface.

38. A microarray structure synthesized according to the method of claim 30, wherein the structure comprises a surface and a plurality of sample-containing spots disposed on the surface.