Method for reducing bias in amperometric sensors

• US 5,653,863 A
• Filed: 05/09/1996
• Issued: 08/05/1997
• Est. Priority Date: 05/05/1995
• Status: Expired due to Term

• Current Assignee: Bayer Healthcare LLC (Bayer AG)
• Original Assignee: Bayer Corporation (Bayer AG)
• Inventors: Yip, Kin Fai, Huang, Dijia, Musho, Matthew K., Genshaw, Marvin A.
• Primary Examiner(s): Gorgos, Kathryn L.
• Assistant Examiner(s): NOGUEROLA, ALEXANDER STEPHAN
• Application Number:
  US08/647,219
• Time in Patent Office: 453 Days
• Field of Search: 204/401, 204/402, 204/403, 204/406, 205/775, 205/777.5
• US Class Current: 205/777.5
• CPC Class Codes: C12Q 1/004 mediator-assisted

Abstract

Apparatus and method are provided for determining the concentration of an analyte in a fluid test sample by applying the fluid test sample to the surface of a working electrode which is electrochemically connected to a reference electrode which surface bears a composition comprising an enzyme specific for the analyte. A mediator is reduced in response to a reaction between the analyte and the enzyme. An oxidizing potential is applied between the electrodes to return at least a portion of the mediator back to its oxidized form before determining the concentration of the analyte to thereby increase the accuracy of the analyte determination. Following this initially applied potential, the circuit is switched to an open circuit or to a potential that substantially reduces the current to minimize the rate of electrochemical potential at the working electrode. A second potential is applied between the electrodes and the current generated in the fluid test sample is measured to determine analyte concentration. Optionally, the accuracy of the analyte determination is further enhanced algorithmically.

Claims

1. In a method for determining the concentration of an analyte in a fluid test sample by applying the fluid test sample to the surface of a working electrode which is electrochemically connected to a reference electrode which surface bears a composition comprising an enzyme specific for the analyte, a mediator which is reduced in response to a reaction between the analyte and the enzyme, which mediator has undergone partial reduction, and then determining the concentration of the analyte in the fluid test sample as a function of the current which passes through the fluid test sample by measuring the current between the working and reference electrodes which results from the amount of reduced mediator produced during storage of the sensor at ambient conditions and during the time period prior to the current measurement period and which is measured at the working electrode by applying a sufficient potential between the working and reference electrode to oxidize the reduced mediator at a time interval on the order of seconds after applying the potential, the improvement which comprises increasing the accuracy of the analyte determination by applying an oxidizing potential between the electrodes to return at least a portion of the mediator back to its oxidized form so as to undo previous reduction of the mediator that occurred before use of the electrodes and switching the system to an open circuit or to a potential that substantially reduces the current to minimize the rate of electrochemical reaction at the working electrode for a set delay period before determining the concentration of the analyte by applying a second potential between the electrodes and then measuring the current generated in the fluid test sample.

2. The method of claim 1 wherein the accuracy of the analyte determination is further increased by:

a) determining the current (i₁) during the application of the positive pulse and the current (i₂) at the end of the application of the second potential, and

b) calculating the analyte level G by solving the equation;

##EQU10## where Int and slope are the intercept and slope of i₂, k is a partial correction factor with a value from 0 to 1, Δ

(i₁, i₂) is an error correction term proportional to the background bias calculated as;

##EQU11## where s₁ =slope of i₁

i_1-lo =i₁ at a low analyte level, and

i_2-lo =i₂ at a low analyte level.

3. The method of claim 2 wherein the analyte is glucose.

4. The method of claim 1 wherein the mediator is a ferricyanide salt.

5. The method of claim 1 further including the step of providing a selected time delay after applying said oxidizing potential before said second potential is applied.

6. The method of claim 5 wherein said step of providing a selected time delay includes the step of waiting a selected time delay in a range between 10 seconds and 40 seconds before said second potential is applied and wherein said second potential is applied for a selected time period in a range between 5 seconds and 10 seconds before the step of measuring said current.

7. The method of claim 1 wherein the step of applying said oxidizing potential between the electrodes includes the steps of applying a voltage potential selectively provided in a range between 0.1 volts and 0.9 volts, comparing the measured current with a threshold value and identifying a time interval for applying said voltage potential responsive to a measured current greater than said threshold value.

8. The method of claim 7 wherein said step of identifying a time interval includes identifying a set time interval selectively provided in a range between 5 seconds and 15 seconds.

9. In a method for determining the concentration of an analyte in a fluid test sample by applying the fluid test sample to the surface of a working electrode which surface bears a composition comprising an enzyme specific for the analyte, a mediator which is reduced in response to a reaction between the analyte and the enzyme, which mediator has undergone partial reduction due to ambient conditions, the improvement which comprises:

a) applying a positive potential pulse to the electrode to oxidize at least a portion of the mediator back to its oxidized form and applying a second potential between the electrodes,

b) determining the current (i₁) during the application of the positive pulse and the current (i₂) at the end of the application of the second potential, and

c) calculating the analyte level G by solving the equation;

##EQU12## where Int and slope are the intercept and slope of i₂, k is a partial correction factor with a value from 0 to 1, Δ

(i₁, i₂) is an error correction term proportional to the background bias calculated as;

##EQU13## where s₁ =slope of i₁

i_1-lo =i₁ at a low analyte level, and

i_2-lo =i₂ at a low analyte level.

10. The method of claim 9 wherein the mediator is a ferricyanide salt.

11. The method of claim 10 wherein the analyte is glucose.