Electrochemical sensor

• US 7,545,148 B2
• Filed: 08/03/2005
• Issued: 06/09/2009
• Est. Priority Date: 08/17/2004
• Status: Active Grant

• Current Assignee: Roche Diabetes Care Inc. (Roche Holding AG)
• Original Assignee: Oxford Biosensors Limited
• Inventors: Griffiths, John, Hyland, Mark, Broughall, John Morton, Askew, Herbert Frank, Lorimer, Kevin
• Primary Examiner(s): Nguyen; Vincent Q
• Application Number:
  US11/660,255
• Publication Number:
  US 20070285099A1
• Time in Patent Office: 1,406 Days
• Field of Search: 324/446, 204/400, 205/775
• US Class Current: 324/446
• CPC Class Codes: G01N 27/48 using polarography, i.e. measuring changes in current under a slowly-varying voltage

Abstract

In an electrochemical sensor, the potential difference applied to the electrochemical cell is raised to a measuring value at a rate determined to reduce the transient current. The maximum rate of change of the voltage is set to prevent saturation of an IE converter. The electrochemical cell may contain micro-electrodes as working and reference electrodes. The method may be applied to a battery powered, handheld device.

Claims

1. An electrochemical sensor device comprising:

a potentiostat for applying a potential between working and counter electrodes in electrical contact with a target solution and sampling the current flowing between the electrodes;

a controller for controlling the potentiostat so that it applies a time varying potential having a ramp-up period, during which the potential difference increases from a first predetermined potential to a second predetermined potential, followed by a plateau period during which said potential difference is maintained substantially constant at said second predetermined potential and samples the current flowing between said working and counter electrodes for measurement purposes, only during said plateau period.

2. A device according to claim 1 wherein the controller is adapted to control the potentiostat so that the rate of potential change in the ramp-up period is less than or equal to about 250Vs⁻

1, preferably less than about 150Vs<sup>−

1</sup> and most preferably in the range of from about 5 to 75Vs<sup>−

1</sup>.

3. A device according to claim 1 wherein the controller is further adapted to control the potentiostat so that the time-varying potential further comprises a second ramp-up period during which the potential difference increases from a third predetermined potential to a fourth predetermined potential, and a second plateau period during which said potential difference is maintained substantially constant at said fourth predetermined potential;

and to sample said current during said second plateau period.

4. A device according to claim 3 wherein the fourth predetermined potential is of the opposite polarity to the second predetermined potential.

5. A device according to claim 1 wherein the potential difference in the ramp-up period(s) substantially follows a part of a sinusoidal function, in particular half a period.

6. A device according to claim 1 wherein the potential difference in the ramp-up period(s) substantially follows a part of a function selected from the group comprising a linear sweep, logarithmic functions, sigmoidal functions, hyperbolas, logistic functions, Weibull functions, a Gompertz growth model, a Hill function, and a Chapman model.

7. A device according to claim 1 wherein said first potential is an open circuit potential.

8. A device according to claim 1 wherein said third potential is an open circuit potential.

9. A device according to claim 1 wherein said electrodes are micro-electrodes, microband electrodes or a micro-electrode array.

10. A device according to claim 1 further comprising a waveform generator arranged to generate the waveform of the potential difference in the ramp-up period(s) in real time.

11. A device according to claim 1 further comprising a memory for storing a plurality of values representing the waveform to be applied to said electrodes and wherein said controller is adapted to read said values in sequence from said memory.

12. A device according to claim 1 wherein said device is battery powered and hand held.

13. An electrochemical sensing method comprising:

applying a time-varying potential between working and reference electrodes in electrical contact with a target solution, using a potentiostat containing an IE converter said time varying potential having a ramp-up period, during which the potential difference increases from a first predetermined potential to a second predetermined potential, followed by a plateau period during which said potential difference is maintained substantially constant at said second predetermined potential; and

sampling the current flowing between said working and counter electrodes for measurement purposes, only during said plateau period,

wherein the inncrease of the potential difference in the ramp-up period has a maximum rate that is set to prevent saturation of the IE converter.

14. A method according to claim 13 wherein the rate of potential change in the ramp-up period is less than or equal to about 250Vs⁻

1, preferably less than about 150Vs<sup>−

1</sup> and most preferably in the range of from about 5 to 75Vs<sup>−

1</sup>.

15. A method according to claim 13 wherein the time-varying potential further comprises a second ramp-up period during which the potential difference increases from a third predetermined potential to a fourth predetermined potential, and a second plateau period during which said potential difference is maintained substantially constant at said fourth predetermined potential;

and the method further comprising sampling said current during said second plateau period.

16. A method according to claim 15 wherein the fourth predetermined potential is of the opposite polarity to the second predetermined potential.

17. A method according to claim 15 wherein the fourth predetermined potential is of a different magnitude than the second predetermined potential.

18. A method according to claim 13 wherein the potential difference in the ramp-up period(s) substantially follows a part of a sinusoidal function, in particular half a period.

19. A method according to claim 13 wherein the potential difference in the ramp-up period(s) substantially follows a part of a function selected from the group comprising a linear sweep, logarithmic functions, sigmoidal functions, hyperbolas, logistic functions, Weibull functions, a Gompertz growth model, a Hill function, and a Chapman model.

20. A method according to claim 13 wherein the waveform of the potential difference in the ramp-up period(s) is calculated in real time.

21. A method according to claim 13 wherein said first potential is an open circuit potential.

22. A method according to claim 13 wherein said third potential is an open circuit potential.

23. A method according to claim 13 wherein said electrodes are micro-electrodes, microband electrodes or a micro-electrode array.