PIEZORESISTIVE CANTILEVER BASED NANOFLOW AND VISCOSITY SENSOR FOR MICROCHANNELS

• US 20080011058A1
• Filed: 03/19/2007
• Published: 01/17/2008
• Est. Priority Date: 03/20/2006
• Status: Abandoned Application

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Cohen, Dan, Quist, Arjan, Chand, Ami, Lal, Ratnesh
• Application Number:
  US11/688,064
• Publication Number:
  US 20080011058A1
• Time in Patent Office: Days
• US Class Current: 73/54.23
• CPC Class Codes: B82Y 35/00 Methods or apparatus for measurement or analysis of nanostructures
• CPC Class Codes: G01N 2291/0256 Adsorption, desorption, surface mass change, e.g. on biosensors
• CPC Class Codes: G01N 2291/02818 Density, viscosity
• CPC Class Codes: G01N 2291/02836 Flow rate, liquid level
• CPC Class Codes: G01N 29/022 Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices microdevices per se B81B
• CPC Class Codes: G01N 29/032 by measuring attenuation of acoustic waves
• CPC Class Codes: G01Q 20/04 Self-detecting probes, i.e. wherein the probe itself generates a signal representative of its position, e.g. piezoelectric gauge
• CPC Class Codes: G01Q 30/14 Liquid environment

Abstract

This invention provides a sensor to measure physical and/or chemical properties of viscous fluids. The sensor is based on microfabricated piezoresistive cantilevers. Deflection of these cantilevers is read out using, e.g., a wheatstone bridge to amplify and convert the deflection into a voltage output. The cantilevers and/or tips attached thereto, can be chemically or physically modified using reagents specific to interact with analytes to be detected in the fluid. The cantilevers can be integrated in a microfluidic system for easy fluid handling and the ability to manage small quantities of fluids.

Claims

1. A device for measuring physical and/or chemical properties of fluids or analytes in fluids at a nanoscale, said device comprising a piezoresistive microcantilever, said microcantilever having a spring constant of less than about 0.6 N/m.

2. The device of claim 1, wherein said microcantilever has a spring constant of less than about 0.4 N/m.

3. The device of claim 1, wherein said microcantilever has a spring constant that ranges from about 0.2 N/m to about 0.3 N/m.

4. The device of claim 1, wherein said microcantilever has a thickness of less than about 5.0 μ

m at least one location.

5. The device of claim 1, wherein said microcantilever has a thickness of less than about 3.0 μ

m at least one location.

6. The device of claim 1, wherein said microcantilever comprises at least one lever of length less than about 100 μ

m.

7. The device of claim 1, wherein said microcantilever comprises at least one lever of length less than about 75 μ

m.

8. The device of claim 1, wherein said microcantilever comprises at least one lever of length about 50 μ

m.

9. The device of claim 1, wherein said microcantilever comprises a material selected from the group consisting of silicon, carbon, germanium, tungsten, nickel, silicon nitride, and silicon oxide.

10. The device of claim 1, wherein said device further comprises a sensing tip attached to said microcantilever.

11. The device of claim 10, wherein said microcantilever has a spring constant at least five-fold less than said sensing tip.

12. The device of claim 10, wherein said microcantilever has a spring constant at least 10-fold less than said sensing tip.

13. The device of claim 10, wherein said sensing tip comprises a carbon nanotube.

14. The device of claim 10, wherein said sensing tip comprises a silicon structure.

15. The device of claim 10, wherein said sensing tip comprises a carbon cone, a carbon nanotube, a nanowire, diamond, silicon nitride, silicon oxide.

16. The device of claim 10, wherein said microcantilever and/or sensing tip is coated with a magnetic or non-magnetic metal layer.

17. The device of claim 19, wherein said metal layer functions as a chemical catalyst, a magnetic field sensor, or a capacitance sensor.

18. The device of claim 10, wherein said cantilever and/or sensing tip is functionalized with an agent selected from the group consisting of a hydroxyl, an amino, a carboxyl, and a thiol and/or a binding moiety selected from the group consisting of a nucleic acid, an antibody, a polypeptide, a sugar, a lectin, a carbohydrate, a cell, a receptor, a small organic molecule, an avidin, a streptavidin, a biotin, and a protein.

19. The device of claim 10, wherein said sensing tip is disposed in a microchannel.

20. The device of claim 1, wherein said device comprises a plurality of microcantilevers.

21. The device of claim 20, wherein said device comprises at least 10 microcantilevers.

22. The device of claim 20, wherein each of said plurality of microcantilevers bears a sensing tip.

23. The device of claim 22, different sensing tips are functionalized with agents that bind different analytes.

24. The device of claim 1, wherein said device is coupled to an instrument to measure electrical resistance changes in said microcantilever.

25. A piezoresistive microcantilever, said microcantilever having a spring constant of less than about 0.6 N/m.

26. The microcantilever of claim 25, wherein said microcantilever has a spring constant of less than about 0.4 N/m.

27. The microcantilever of claim 25, wherein said microcantilever has a spring constant that ranges from about 0.2 N/m to about 0.3 N/m.

28. The microcantilever of claim 25, wherein said microcantilever has a thickness of less than about 5.0 μ

m at least one location.

29. The microcantilever of claim 25, wherein said microcantilever has a thickness of less than about 3.0 μ

m at least one location.

30. The microcantilever of claim 25, wherein said microcantilever comprises at least one lever of length less than about 100 μ

m.

31. The microcantilever of claim 25, wherein said microcantilever comprises at least one lever of length less than about 75 μ

m.

32. The microcantilever of claim 25, wherein said microcantilever comprises at least one lever of length about 50 μ

m.

33. The microcantilever of claim 25, wherein said microcantilever comprises a material selected from the group consisting of silicon, carbon, germanium, tungsten, nickel, silicon nitride, and silicon oxide.

34. A method of measuring the flow rate or viscosity of a fluid, said method comprising:

contacting said fluid with a device comprising a piezoresistive microcantilever, said microcantilever having a spring constant of less than about 0.6 N/m; and

measuring the electrical resistance or electrical conductivity of said microcantilever wherein the electrical resistance or electrical conductivity provides a measure of the deflection of said microcantilever which provides a measure of flow rate and/or viscosity of said fluid.

35. The method of claim 34, wherein said fluid is in a microchannel.

36. A method of detecting the presence or quantity of an analyte in a solution, said method comprising:

contacting said solution with a device comprising a piezoresistive microcantilever, said microcantilever having a spring constant of less than about 0.6 N/m, wherein said microcantilever is attached to a sensing tip that is functionalized with an agent that binds said analyte; and

detecting deflection of said microcantilever wherein deflection of said microcantilever provides a measure of presence or amount of analyte bound to said tip.

37. The method of claim 36, wherein said detecting comprises detecting the conductance or resistivity of said microcantilever.

38. The method of claim 36, wherein said tip is functionalized with an agent selected from the group consisting of a hydroxyl, an amino, a carboxyl, and a thiol and/or a binding moiety selected from the group consisting of a nucleic acid, an antibody, a polypeptide, a sugar, a lectin, a carbohydrate, a cell, a receptor, a small organic molecule, an avidin, a streptavidin, a biotin, and a protein.

39. The method of claim 36, wherein said contacting is in a microchannel or microchamber.

40. A method of fabricating a piezoresistive microcantilever, said method comprising:

providing a device layer on a substrate wherein said device layer comprises a microcantilever;

micromachining said microcantilever to dimensions providing a spring constant of less than about 0.6 N/m.

41. The method of claim 40, wherein said micromachining comprises micro-milling using a focused ion beam.

42. The method of claim 40, wherein said microcantilever is machined to dimensions providing a spring constant of less than about 0.4 N/m.

43. The method of claim 40, wherein said microcantilever is machined to dimensions providing a spring constant that ranges from about 0.2 N/m to about 0.3 N/m.

44. The method of claim 40, wherein said microcantilever is machined to a thickness of less than about 5.0 μ

m at least one location.

45. The method of claim 40, wherein said microcantilever is machined to a thickness of less than about 3.0 μ

m at least one location.

46. The method of claim 40, wherein said microcantilever is machined to comprise at least one lever of length less than about 100 μ

m.

47. The method of claim 40, wherein said microcantilever is machined to comprise at least one lever of length less than about 75 μ

m.

48. The method of claim 40, wherein said microcantilever is machined to comprise least one lever of length about 50 μ

m.

49. The method of claim 40, wherein said method further comprises depositing a sensing tip attached to said microcantilever.

50. The method of claim 49, wherein said sensing tip comprises a carbon nanotube or a nanowire.