Open circuit potential amperometry and voltammetry

• US 20020180446A1
• Filed: 03/14/2002
• Published: 12/05/2002
• Est. Priority Date: 03/23/2001
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California), North Carolina State University (University of North Carolina System)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Lindsey, Jonathan S., Roth, Kristian A., Bocian, David, Kuhr, Werner
• Granted Patent: US 6,921,475 B2
• Time in Patent Office: Days
• US Class Current: 324/432
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: G01N 27/3277 being a redox reaction, e.g. detection by cyclic voltammetry voltammetry per se G01N27/42, G01N27/48

Abstract

This invention provides approaches to improve the signal to noise ratio (S/N) in electrochemical measurements (e.g. amperometry, voltammetry, etc.). In particular, a method is described wherein the faradaic current is temporally dissociated from the charging current associated with reading the charge of a redox-active species (e.g. a self-assembled monolayer (SAM)). This method, designated herein as open circuit potential amperometry (OCPA), quantitatively reads the charge of the redox species bound to (electrically coupled to) an electrode surface, while discriminating against both charging current(s) and amperometric signal(s) that arise, e.g. from diffusion-based species in solution.

Claims

1. A method of determining the oxidation state of a compound, said method comprising:

disconnecting an electrode from an electrochemical cell comprising said compound to allow said cell to reach an open circuit potential (OCP);

connecting said electrochemical cell to an externally applied potential equivalent to said open circuit potential; and

detecting a resulting current if said current exists wherein the magnitude of said current is a measure of the oxidation state of said compound.

2. The method of claim 1, wherein said compound is oxidized and said open circuit potential is a reducing potential.

3. The method of claim 1, wherein said compound is reduced and said open circuit potential is an oxidizing potential.

4. The method of claim 1, wherein said disconnecting is for a period ranging from about 1 μ

s to about 1000 seconds.

5. The method of claim 1, wherein said disconnecting is for a period sufficient to dissipate charge in said cell.

6. The method of claim 1, wherein said disconnecting is for a period comparable to the RC time constant of said cell.

7. The method of claim 1, wherein said electrochemical cell a member of an array of electrochemical cells.

8. The method of claim 7, wherein said array of electrochemical cells comprises at least 100 electrochemical cells.

9. The method of claim 1, wherein said disconnecting and said connecting comprise disconnecting and connecting the same electrode.

10. The method of claim 1, wherein said disconnecting and said connecting comprise making or breaking an electrical connection.

11. The method of claim 1, wherein said disconnecting and said connecting comprise varying a resistance between an electrode and said cell.

12. The method of claim 1, wherein said open circuit potential varies from about ±

0.001V to about ±

5V.

13. The method of claim 1, wherein said compound has a multiplicity of different and distinguishable non-zero oxidation states.

14. The method of claim 1, wherein said potential is applied through a voltage follower.

15. The method of claim 1, wherein said potential is applied through a counter electrode while a working electrode is held at ground.

16. The method of claim 1, wherein said detecting comprises amplifying said current with a high bandwidth current amplifier.

17. The method of claim 1, wherein said detecting is with a current transducer.

19. The method of claim 18, wherein said compound is oxidized and said open circuit potential is a reducing potential.

20. The method of claim 18, wherein said compound is reduced and said open circuit potential is an oxidizing potential.

21. The method of claim 18, wherein said disconnecting is for a period ranging from about 1 μ

s to about 1000 seconds.

22. The method of claim 18, wherein said disconnecting is for a period sufficient to dissipate charge in said cell.

23. The method of claim 18, wherein said disconnecting is for a period comparable to the RC time constant of said cell.

24. The method of claim 18, wherein said electrochemical cell a member of an array of electrochemical cells.

25. The method of claim 24, wherein said array of electrochemical cells comprises at least 100 electrochemical cells.

26. The method of claim 18, wherein said disconnecting and said connecting comprise disconnecting and connecting the same electrode.

27. The method of claim 18, wherein said disconnecting and said connecting comprise making or breaking an electrical connection.

28. The method of claim 18, wherein said disconnecting and said connecting comprise varying a resistance between an electrode and said cell.

29. The method of claim 18, wherein said open circuit potential varies from about ±

0.01V to about ±

5V.

30. The method of claim 18, wherein said compound has at least two different and distinguishable non-zero oxidation states.

31. The method of claim 18, wherein said potential is applied through a voltage follower.

32. The method of claim 18, wherein said detecting comprises amplifying said current with a high bandwidth current amplifier.

18. A method of determining the oxidation state of a compound, said method comprising:

applying a series of incrementally increasing voltage pulses to said compound in an electrochemical cell;

disconnecting an electrode from said electrochemical cell, after each pulse, to allow said cell to reach an open circuit potential (OCP);

connecting said electrochemical cell to an externally applied potential equivalent to said open circuit potential; and

detecting a resulting current if said current exists wherein the magnitude of said current is a measure of the oxidation state of said compound.

33. A device for the detection of an oxidation state of a compound, said device comprising:

a first electrode and a second electrode disposed to contact said compound and thereby form an electrochemical cell;

a voltage source connected to said first electrode;

a switch that allows said compound to be isolated from said voltage source and said electrochemical cell to reach an open circuit potential; and

a current transducer for measuring current produced by said electrochemical cell.

34. The device of claim 33, wherein said device comprises two or more electrochemical cells.

35. The device of claim 34, wherein said device comprises ten or more electrochemical cells.

36. The device of claim 33, wherein said voltage source comprises a voltage follower.

37. The device of claim 33, wherein said current meter comprises a broadband current amplifier.

38. The device of claim 33, wherein said first electrode and said second electrode are disposed in a channel through which a fluid comprising said compound can pass.

39. The device of claim 38, wherein said channel is a capillary tube.

40. The device of claim 38, wherein said is a channel on a chip.

41. The device of claim 33, wherein said electrodes are disposed in a well.

42. The device of claim 33, wherein said electrodes are disposed on a biosensor.

43. The device of claim 33, wherein said electrodes are components of a molecular memory.

44. A molecular memory device comprising:

a first electrode and a second electrode disposed to contact a redox-active compound comprising a porphyrinic macrocycle and thereby form an electrochemical storage cell wherein said first and second electrodes are fixed electrodes;

a voltage source connected to said first electrode;

a switch that allows said compound to be isolated from said voltage source and said storage cell to reach an open circuit potential; and

a current transducer for measuring current produced by said electrochemical cell.

45. The device of claim 44, wherein said device comprises two or more electrochemical cells.

46. The device of claim 45, wherein said device comprises ten or more electrochemical cells.

47. The device of claim 44, wherein said voltage source comprises a voltage follower.

48. The device of claim 44, wherein said current meter comprises a broadband current amplifier.

49. The device of claim 44, wherein said porphyrinic macrocycle is a porphyrin.