Electrical current for controlling fluid parameters in microchannels

Claims

What is claimed is:

1. A method of elevating temperature in at least a portion of a fluid-filled channel disposed in a substrate, to a selected elevated temperature, comprising:

applying a selectable current through a fluid in the at least a portion of the fluid-filled channel, the portion of the fluid-filled channel having a electrical resistance;

controlling at least one of the selectable current or the electrical resistance to elevate the temperature in the portion of the channel to the selected elevated temperature.

2. The method of claim 1, further comprising transporting a material through at least the portion of the channel to elevate the temperature of the material to the selected elevated temperature.

3. The method of claim 1, wherein the portion of the channel is at least a first portion and the selected elevated temperature is a first selected elevated temperature, and further comprising maintaining at least a second portion of the channel at a second temperature lower than the first selected elevated temperature.

4. The method of claim 3, further comprising providing the first portion of the channel with a narrowed cross-sectional area relative to the second portion of the channel; and

wherein the controlling step comprises applying a constant current through a fluid in the first and second portions of the channel.

5. The method of claim 3, comprising repeatedly transporting a material between the at least first portion of the channel and the at least second portion of the channel to cycle a temperature of the material between the first selected elevated temperature and the second temperature.

6. The method of claim 5, wherein the material comprises reagents for performing a nucleic acid amplification reaction.

7. The method of claim 6, wherein the nucleic acid amplification reaction is selected from the group consisting of a polymerase chain reaction and a ligase chain reaction.

8. The method of claim 2, wherein the transporting of the material comprises electrokinetically transporting the material through the at least first portion.

9. The method of claim 8, wherein the selectable current is a first selectable current, and wherein the step of electrokinetically transporting the material comprises applying a second selectable current through the channel to electrokinetically transport a material along the first channel.

10. The method of claim 9, wherein the first selectable current comprises an alternating current and the second selectable current comprises a direct current.

11. The method of claim 8, wherein electrokinetically transporting the material through the channel comprises electroosmotically transporting the material through the channel.

12. The method of claim 8, wherein electrokinetically transporting the material through the channel comprises electrophoretically transporting the material through the channel.

13. The method of claim 1, wherein the fluid-filled channel is disposed in a substrate, and further comprising the step of maintaining a global temperature of the substrate at a selected level above or below ambient temperature.

14. The method of claim 1, wherein the channel is a first channel, and the applying step comprises:

providing at least a second channel intersecting the first channel at the portion of the first channel; and

applying the first selectable current through the second channel and the portion of the first channel.

15. The method of claim 1, wherein the controlling step further comprises sensing a temperature in the portion of the channel, and increasing or decreasing the selectable current based upon the temperature sensed.

16. The method of claim 15, wherein the sensing step comprises determining a relative electrical resistance through the fluid in the portion of the channel, the relative electrical resistance being indicative of the temperature of the fluid in at least the portion of the channel.

17. A method of heating fluid in a microfluidic system, said method comprising steps of;

providing a channel having a first end, a second end, and a region defined therebetween, said channel being disposed in a substrate;

providing fluid in said region of said channel;

applying an electric current through said fluid to heat said fluid at said region;

wherein said electric current selectively heats said fluid in said region of said channel while preventing substantial heating of said fluid outside said region.

18. The method of claim 17, wherein said channel is an annular region.

19. The method of claim 17, wherein said current is applied using a voltage bias applied directly to said fluid.

20. The method of claim 19, wherein said voltage bias is applied directly to said fluid using a pair of electrodes.

21. The method of claim 17, wherein said region has a smaller cross-section relative to a cross-section of said channel at said first end.

22. The method of claim 17, wherein said region has a smaller cross-section relative to a cross-section of said channel at said second end.

23. The method of claim 17, wherein said current is DC, AC, or arbitrary.

24. The method of claim 17, wherein said fluid contains materials selected from the group consisting of samples, analytes, buffers and reagents.

25. The method of claim 17, wherein said channel comprises a cross-section ranging from about 0.1 .mu.m to about 500 .mu.m.

26. The method of claim 17, wherein said region is disposed in said substrate adjacent to a second fluid-filled channel disposed in said substrate, but wherein said region is not in direct fluid communication with said second channel.

27. The method of claim 17, further comprising a step of moving said fluid in said channel, said step of moving comprising the steps of applying a voltage bias to said fluid to move said fluid between said first end and said second end.

28. The method of claim 17, wherein said voltage bias is provided by DC.

29. The method of claim 17, wherein said applying step occurs successively to heat and cool said fluid in said region; wherein said applying step selectively heats and cools said fluid in said region of said channel while preventing substantial heating of said fluid outside said region.

30. The method of claim 29, wherein said fluid comprises a nucleic acid material.

31. The method of claim 29, wherein said steps occur in a nucleic acid amplification process.

32. The method of claim 31, wherein the nucleic acid amplification process is selected from the group consisting of PCR and LCR.

33. A method of controlling temperature of fluid in a channel defined in a substrate of a microfluidic system, said method comprising steps of:

applying an electrical energy source to begin heating said fluid in said channel; and

adjusting a first parameter applied from said electrical energy source to said fluid to provide a relatively constant second parameter in said fluid, wherein said first parameter is current, voltage, power or a combination thereof, and the second parameter is resistance and conductivity; and

wherein said fluid is heated without substantially increasing a temperature of said substrate.

34. The method of claim 33, wherein said first parameter is voltage.

35. The method of claim 33, wherein said first parameter is electric current.

36. The method of claim 33, wherein said second parameter is conductivity.

37. The method of claim 33, wherein said applying step occurs successively to heat and cool said fluid in said channel.

38. The method of claim 33, wherein said fluid is heated in a portion of said channel.