Electropipettor and compensation means for electrophoretic bias

• US 20030085126A1
• Filed: 12/18/2002
• Published: 05/08/2003
• Est. Priority Date: 06/28/1996
• Status: Active Grant

• Current Assignee: Caliper Life Sciences Incorporated (Revvity, Inc.)
• Original Assignee: Caliper Technologies Corp (Revvity, Inc.)
• Inventors: Parce, J. Wallace, Knapp, Michael R.
• Granted Patent: US 7,001,496 B2
• Time in Patent Office: Days
• US Class Current: 204/450
• 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 33/30351 using hydrophilic/hydrophobic surfaces
• CPC Class Codes: B01F 33/30352 using roughness of the surfaces
• CPC Class Codes: B01J 19/0093 Microreactors, e.g. miniaturised or microfabricated reactors laboratory containers with capillary fluid transport in microfabricated channels or chambers B01L3/5027
• CPC Class Codes: B01J 2219/00891 Feeding or evacuation
• CPC Class Codes: B01L 2200/027 for microfluidic devices
• CPC Class Codes: B01L 2400/0415 electrical forces, e.g. electrokinetic
• CPC Class Codes: B01L 2400/0418 electro-osmotic flow [EOF]
• CPC Class Codes: B01L 2400/0421 electrophoretic flow
• CPC Class Codes: B01L 3/021 Pipettes, i.e. with only one conduit for withdrawing and redistributing liquids
• CPC Class Codes: B01L 3/502715 characterised by interfacing components, e.g. fluidic, electrical, optical or mechanical interfaces
• CPC Class Codes: B01L 3/50273 characterised by the means or forces applied to move the fluids micropumps F04B19/006, of the membrane type F04B43/043
• CPC Class Codes: B01L 3/502784 specially adapted for droplet or plug flow, e.g. digital microfluidics automatic analysis using a stream of discrete samples in a tube system G01N35/08
• CPC Class Codes: F04B 17/00 Pumps characterised by combination with, or adaptation to, specific driving engines or motors
• CPC Class Codes: F04B 19/006 Micropumps F04B43/043 and F04B43/095 take precedence
• CPC Class Codes: G01N 27/44704 Details; Accessories
• CPC Class Codes: G01N 27/44743 Introducing samples
• CPC Class Codes: G01N 27/44791 Microapparatus sample containers with integrated microfluidic structures B01L3/5027
• CPC Class Codes: H02N 11/006 Motors
• CPC Class Codes: Y10S 366/02 Micromixers: segmented laminar flow with boundary mixing orthogonal to the direction of fluid propagation with or without geometry influences from the pathway
• CPC Class Codes: Y10T 436/113332 : with conveyance of sample along a test line in a container or rack
• CPC Class Codes: Y10T 436/2575 : Volumetric liquid transfer

Abstract

A channel (140) is divised into portions (142, 144). The sidewalls of each channel portion (142, 144) have surface charges of opposite polarity. The two channel portions (142, 144) are physically connected together by a salt bridge (133), such as a glass frit or gel layer. The salt bridge (133) separates the fluids in channel (140) from an ionic fluid reservoir (135). To impart electroosmotic and electrophoretic forces along the channel (140) between parts A and B, respectively. Additionally, a third electrode (137) is placed in the reservoir (135).

Claims

1. A microfluidic system with compensation for electrophoretic bias, comprising

a capillary channel having sides, a first end and a second end, said capillary channel further divided into first and second portions, said sides of said first and second portions having surface charges of opposite polarities;

and

a first electrode at said first end;

a second electrode between said first and second portions of said capillary channel; and

a third electrode at said second end, said first, second and third electrodes set at voltages such that a fluid is electroosmotically pumped through said first and second portions from said first end to said second end, and electrophoretic movement in said second portion is opposite to electrophoretic movement in said first portion.

2. The microfluidic system of claim 1 wherein said first and second portions of said capillary channel each have surface charge densities, said surface charge densities approximately equal.

3. The microfluidic system of claim 2 wherein said first and second portions of said capillary channel each have volumes, said volumes approximately equal.

4. The microfluidic system of claim 1 wherein said sides of at least one of said portions of said capillary channel are defined by a film, said film having said surface charge of said one portion.

5. A microfluidic system with compensation for electrophoretic bias, comprising

a first capillary channel;

a second capillary channel intersecting said first capillary channel; and

a chamber at said intersection of said first and second capillary channels shaped such that a region containing subject material moving from said first capillary channel to said second capillary channel is mixed to compensate for electrophoretic bias in moving along said first capillary channel.

6. The microfluidic system of claim 5 wherein said chamber is defined by sides along a first capillary channel length funneling into said second capillary channel.

7. The microfluidic system of claim 6 wherein said chamber sides are straight.

8. The microfluidic system of claim 6 wherein said second capillary channel width is approximately equal to a length of said subject material region.

9. The microfluidic system of claim 5 wherein said subject material has a diffusion constant and said second capillary channel has a width such that said subject material diffuses across said second channel width before being diverted from said second channel.

10. The microfluidic system of claim 9 wherein said subject material has a diffusion constant of approximately 1×

10<sup>−

5</sup> cm²/sec. and said second channel width is approximately 10 μ

m.

11. An electropipettor for introducing materials into a microfluidic system, said electropipettor fluidly connected to said microfluidic system, said electropipettor comprising

a capillary channel having an end for contacting at least one source of said materials;

and

a voltage source for applying a voltage between said one source of said materials and a second electrode in said microfluidic system when said capillary channel end contacts said one source of said materials such that material from said one source is electrokinetically introduced into said electropipettor toward said microfluidic system.

12. The electropipettor of claim 11 wherein said capillary channel has a cross-sectional area of approximately 10-100 (μ

m)².

13. The electropipettor of claim 11 wherein said voltage source applies a negative voltage to said first electrode with respect to said second electrode.

14. The electropipettor of claim 11 wherein said capillary channel is defined in a substrate and by a cover element over said substrate.

15. An electropipettor for introducing subject materials into a microfluidic system, said electropipettor fluidly connected to said microfluidic system, said electropipettor comprising

a first capillary channel having a first end for contacting at least one source of said subject materials and a second end terminating in said microfluidic system;

a second capillary channel having a first end terminating near said first end of said first capillary channel and a second end terminating in a source of first spacer material;

a voltage source for applying voltages between said at least one subject material source and said microfluidic system, and between said first spacer material source and said microfluidic system such that subject material from said one subject material source and spacer material from said first spacer material source are electrokinetically introduced into said electropipettor toward said microfluidic system.

16. The electropipettor of claim 15 further comprising

a third capillary channel having a first end terminating near said first end of said first capillary channel and a second end terminating in a source of second spacer material;

and wherein

said voltage source applies voltages to said second spacer material source and said microfluidic system such that subject material from said second spacer material source is electrokinetically introduced into said electropipettor toward said microfluidic system.

17. The electropipettor of claim 16 wherein said first spacer material source holds spacer material of ionic concentration orders of magnitude greater than that of said second spacer material source.

18. The electropipettor of claim 15 further comprising an electrode disposed along said first capillary channel such that said electrode contacts said subject material source when said first capillary channel end is placed into at least one source of said subject materials;

and said voltage source is connected to said electrode to apply voltages between said at least one subject material source and said microfluidic system.

19. The electropipettor of claim 15 wherein said first and second capillary channels are defined in a substrate and by a cover element over said substrate.

40. A sampling system comprising:

an electropipettor of claim 16;

a sample substrate, said sample substrate having a plurality of different samples immobilized thereon; and

a translation system for moving said electropipettor relative to said sample substrate.

41. The sampling system of claim 40, wherein said first end of said first capillary channel and said first end of said second capillary channel terminate in a fluid retention well at a tip of said electropipettor.

42. The sampling system of claim 40, wherein said plurality of different samples are dried onto a surface of said sample substrate, and wherein said electropipettor is capable of expelling an amount of a fluid to resolubilize said sample on said sample substrate.

43. The sampling system of claim 42, wherein said samples are applied to said sample substrate surface in a fluid form, and said substrate surface comprises a plurality of fluid localization regions.

44. The sampling system of claim 43, wherein said fluid localization regions comprise relatively hydrophilic regions surrounded by relatively hydrophobic regions.

45. The sampling system of claim 43, wherein said fluid localization regions comprise relatively hydrophobic regions surrounded by relatively hydrophilic regions.

46. The sampling system of claim 43, wherein said fluid localization regions comprise depressions on said surface of said sample substrate.

20. A method of introducing materials from a plurality of sources into a microfluidic system, said microfluidic system having a capillary channel having an end, a voltage source for applying a voltage potential to an electrode in said microfluidic system, said method comprising

contacting said capillary channel end to a subject material source;

applying a voltage to said subject material source with respect to said electrode such that subject material from said source is electrokinetically introduced into said capillary channel toward said microfluidic system;

selecting a source of spacer material, said spacer material having a predetermined ionic concentration;

contacting said capillary channel end into said source of spacer material;

applying a voltage to said spacer material source with respect to said electrode such that said spacer material is electrokinetically introduced into said capillary channel next to said subject material; and

repeating the steps above with different material sources so that a plurality of different materials separated by spacer material is electrokinetically introduced into said capillary channel and transported toward said microfluidic system without intermixing said different materials.

21. The method of claim 20 wherein said spacer material comprises a solution of high ionic strength.

22. The method of claim 20 wherein said spacer material comprises a substantially immiscible fluid.

23. The method of claim 20 wherein said spacer material comprises an ionophore.

24. The method of claim 20 wherein said capillary channel has a cross-sectional area of approximately 10-1000 (μ

m)².

25. The method of claim 20 wherein said steps of contacting said capillary channel end to a source of spacer material and applying a voltage to said spacer material source with respect to said first electrode to electrokinetically introduce said spacer material into said capillary channel, further comprise:

placing said capillary channel end into a source of a first spacer material;

applying a voltage to said first spacer material source with respect to said electrode such that said first spacer material is electrokinetically introduced into said capillary channel;

placing said capillary channel end into a source of a second spacer material;

applying a voltage to said second spacer material source with respect to said electrode such that said second spacer material is electrokinetically introduced into said capillary channel; and

repeating said first two steps above so that said plurality of different subject materials are separated by regions of said first, second and first spacer materials.

26. The method of claim 25 wherein said first spacer material comprises a solution of high ionic strength, and said second spacer material comprises a solution of low ionic strength.

27. The method of claim 20 further comprising disposing a second electrode along said capillary channel to said capillary channel end so that said second electrode contacts a source when said capillary channel end contacts said material or spacer source;

and wherein said voltage applying steps comprise creating a voltage difference between said microfluidic system electrode and said second electrode.

28. The method of claim 20 wherein said voltage applying steps comprise applying a negative voltage to said subject material or spacer sources with respect to said microfluidic system electrode.

29. A microfluidic system for moving a plurality of subject materials from a first location to a second location along a channel, said microfluidic system comprising:

a source for creating a voltage difference across said first location and said second location;

a plurality of subject material regions in said channel, said subject material regions separated by first spacer regions of high ionic strength; and

at least one second spacer region of low ionic concentration.

30. A microfluidic system for transporting a plurality of subject material regions from a first point to a second point on a channel, said microfluidic system comprising:

a pair of first spacer regions on either side of each subject material region, said first spacer regions having high ionic concentrations;

at least one second spacer region, said second spacer region having a low ionic concentration.

31. The microfluidic system of claim 30, wherein said second spacer region has an ionic concentration at least two orders of magnitude less than that said first spacer region.

32. The microfluidic system of claim 31 wherein said second spacer region has an ionic concentration in the range of 1 to 10 mM, and said first spacer regions have ionic concentrations in the range of 100 to 1000 mM.

33. A microfluidic system, comprising:

a substrate having at least a first channel and at least a second channel disposed in said substrate, said at least second channel intersecting said first channel, wherein said first channel is deeper than said second channel; and

an electroosmotic fluid direction system.

34. The microfluidic system of claim 33, wherein said at least first channel is at least twice as deep as said second channel.

35. The microfluidic system of claim 33, wherein said at least first channel is at least five times deeper than said second channel.

36. The microfluidic system of claim 33, wherein said at least first channel is at least about ten times deeper than said second channel.

37. In an electroosmotic fluid direction system, a method of controllably delivering a fluid stream along a first channel, wherein said first channel is intersected by at least a second channel, and wherein said fluid stream comprises at least two fluid regions having different ionic strengths, the method comprising, providing said first channel with a greater depth than said second channel.

38. A method of transporting fluid samples within a microfluidic channel, comprising:

introducing at least a plug of a first fluid material having a first ionic strength into said channel;

introducing at least a first sample fluid plug into said channel;

introducing at least a second fluid material plug having said first ionic strength into said channel;

introducing at least a third fluid material plug having a second ionic strength, said second ionic strength being lower than said first ionic strength; and

applying a voltage across said channel.

39. The method of claim 38, wherein said steps of introducing said at least first fluid material plug, said at least sample fluid plug, said at least second fluid material plug and said at least third fluid material plug comprise:

placing an end of said channel in contact with a source of said at least first fluid material, and applying a voltage from said source of said at least first fluid material to said channel, whereby said first fluid material is introduced into said channel;

placing an end of said channel in contact with a source of said at least first sample fluid and applying a voltage from said source of said at least first sample fluid to said channel, whereby said first sample fluid is introduced into said channel;

placing an end of said channel in contact with a source of said at least second fluid material and applying a voltage from said source of said at least second fluid material to said channel, whereby said second fluid material is introduced into said channel; and

placing an end of said channel in contact with a source of said at least third fluid material and applying a voltage from said source of said at least third fluid material to said channel, whereby said third fluid material is introduced into said channel.

47. The use of a substrate having a channel, in transporting at least a first subject material from at least a first location to a second location along said channel, utilising at least one region of low ionic concentration which is transported along said channel due to an applied voltage.

48. A use of claim 47, in which the ionic concentration of said one region is substantially lower than that of said subject material.

49. A use of claim 47 or claim 48, wherein a plurality of subject materials are transported, separated by high ionic concentration spacer regions.

52. A use of any of claims 47 to 51, in which said substrate is a microfluidic system.

53. A use of any of claims 47 to 51, in which the substrate is an electropipettor.

54. A use of claim 53, in which said electropipettor has a main channel for transportation of said subject material and at least one further channel fluidly connected to said main channel from which a further material to be transported along said main channel is obtained.

55. A use of claim 54, in which said further material is drawn into said main channel as a buffer region between each of a plurality of separate subject materials.

50. The use of a substrate having a channel along which at least a first subject material may be transported, in electrophoretic bias compensation, said channel being divided into a first and a second portion, in which the wall or walls of said channel are oppositely charged, such that electrophoretic bias on said at least first subject material due to transportation in said first portion is substantially compensated for by electrophoretic bias due to transport in said second portion.

51. A use of claim 50 in which a first electrode is located at a remote end of said first portion, a second electrode is located at the intersection between said portions and a third electrode is located at a remote end of said second portion.

56. The use of a microfluidic system having at least a first and a second fluid channel which intersect, in optimising flow conditions, the channels having different depths.

57. A use of claim 56 in which one channel is between 2 to 10 times deeper than the other channel.

58. The use of a microfluidic system having a first channel and a second channel intersecting the first channel, in electrophoretic compensation, the intersection between said channels being shaped such that a fluid being transported along said first channel towards said second channel is mixed at said intersection and any electrophoretic bias in the fluid is dissipated.

59. A microfluidic system comprising a substrate having a channel, in which at least a first subject material is transported from at least a first location to a second location along said channel, utilizing at least one region of low ionic concentration which is transported along said channel due to an applied voltage.

60. The system of claim 59, in which the ionic concentration of said one region is substantially lower than that of said subject material.

61. A system of claim 59 or claim 60, wherein a plurality of subject materials are transported, separated by high ionic concentration spacer regions.

64. An electropipettor comprising a system as claimed in any of claims 59 to 61, or a substrate as claimed in claims 62 or claim 63.

65. An electropipettor as claimed in claim 64, having a main channel for transportation of said subject material and at least one further channel fluidly connected to said main channel from which a further material to be transported along said main channel is obtained.

66. An electropipettor as claimed in claim 65, in which said further material is drawn into said main channel as a buffer region between each of a plurality of separate subject materials.

62. A substrate having a channel along which at least a first subject material may be transported, in electrophoretic bias compensation, said channel being divided into a first and a second portion, in which the wall or walls of said channel are oppositely charged, such that electrophoretic bias on said at least first subject material due to transportation in said first portion is substantially compensated for by electrophoretic bias due to transport in said second portion.

63. A substrate as claimed in claim 62 in which a first electrode is located at a remote end of said first portion, a second electrode is located at the intersection between said portions and a third electrode is located at a remote end of said second portion.

67. A microfluidic system having at least a first and a second fluid channel which intersect, said channels having different depths, in order to optimize flow conditions.

68. A system as claimed in claim 67 in which one channel is between 2 to 10 times deeper than the other channel.

69. A microfluidic system having a first channel and a second channel intersecting said first channel, the intersection between said channels being shaped such that a fluid being transported along said first channel towards said second channel is mixed at said intersection and any electrophoretic bias in said fluid is dissipated.