Method for determination of analyte concentrations and related apparatus

• US 9,005,424 B2
• Filed: 11/25/2013
• Issued: 04/14/2015
• Est. Priority Date: 04/15/2005
• Status: Active Grant

• Current Assignee: Agamatrix Incorporated (AgaMatrix Holdings LLC d/b/a WaveForm Diabetes)
• Original Assignee: Agamatrix Incorporated (AgaMatrix Holdings LLC d/b/a WaveForm Diabetes)
• Inventors: Diamond, Steven, Harding, Ian, Iyengar, Sridhar G., Wei, Baoguo
• Primary Examiner(s): Ball, J. Christopher
• Application Number:
  US14/088,967
• Publication Number:
  US 20140083870A1
• Time in Patent Office: 505 Days
• Field of Search: 20440301-40315, 205/777.5, 205/779, 205/792
• US Class Current: 205/775
• CPC Class Codes: C12Q 1/006 for glucose
• CPC Class Codes: G01N 27/307 Disposable laminated or multilayered electrodes G01N27/3272 takes precedence
• CPC Class Codes: G01N 27/3272 Test elements therefor, i.e. disposable laminated substrates with electrodes, reagent and channels optical biosensors G01N33/52
• CPC Class Codes: G01N 27/3273 Devices therefor, e.g. test element readers, circuitry details not specific to biochemical electrodes G01N33/4875
• CPC Class Codes: G01N 27/4161 measuring the voltage and using a constant current supply, e.g. chronopotentiometry
• CPC Class Codes: G01N 27/4166 measuring a particular property of an electrolyte
• CPC Class Codes: G01N 33/48707 by electrical means G01N33/49, G01N33/493 take precedence

Abstract

A method is provided for determining analyte concentrations, for example glucose concentrations, that utilizes a dynamic determination of the appropriate time for making a glucose measurement, for example when a current versus time curve substantially conforms to a Cottrell decay, or when the current is established in a plateau region. Dynamic determination of the time to take the measurement allows each strip to operate in the shortest appropriate time frame, thereby avoiding using an average measurement time that may be longer than necessary for some strips and too short for others.

Claims

1. A method for determining an analyte in a sample comprising the steps of:

(a) detecting introduction of a sample to be evaluated into an electrochemical test strip having working and counter electrodes and setting the time of detection as t=0;

(b) applying a potential between the electrodes sufficient to generate a diffusion-limited current when analyte is present in the sample;

(c) monitoring the diffusion limited current for a local maximum occurring at a time starting at t=1 second and setting a time, t_peak, as the time at which the local maximum occurs;

(d) sampling the current for determination of analyte at a time, t_meas, wherein t_meas is after t_peak, and t_meas is determined based on the value of t_peak, and

(e) generating an indication of analyte in the sample based on the sampled current value at time t_meas.

2. The method of claim 1, wherein t_meas is set to a₁ X t_peak +a₂ where a₁ and a₂ are empirically determined constants, with the proviso that the value of a₂ can be 0.

3. The method of claim 2, wherein a₁ has a value of 1.25 to 1.35 and a₂ is 0.

4. The method of claim 2, wherein a₁ has a value of 1.5 to 5 and a₂ is 0.

5. The method of claim 1, wherein the time t_test, is dynamically determined for a particular test as equal to t_peak plus a predetermined time interval.

10. The method of claim 5, wherein the plurality of current versus time points to be sampled is restricted according a range dependent on t_peak.

6. A method for determining an analyte in a sample comprising the steps of:

(a) introducing a sample to be evaluated into an electrochemical test strip having working and counter electrodes;

(b) applying a potential between the electrodes sufficient to generate a diffusion-limited current when analyte is present in the sample;

(c) dynamically determining a time, t_peak, as the time when diffusion limiting current at the counter electrode is established;

(d) sampling the current at a time t_test after t_peak to collect a plurality of current versus time data points, and analyzing these data points to identify the time when the current conforms to Cottrell decay, and identifying this time as t_meas, and

(e) generating an indication of analyte in the sample based on the sampled current values at time t_meas.

7. The method of claim 6, wherein the first derivative of the current versus time data points (dI/dt) is evaluated to identify the time when the current conforms to Cottrell decay.

8. The method of claim 6, wherein the second derivative of the current versus time data points (dI²/dt²) is evaluated to identify the time when the current conforms to Cottrell decay.

9. The method of claim 6, wherein the first derivative of the reciprocal of current squared versus time data points (d(1/I²)/dt) is evaluated to identify the time when the current conforms to Cottrell decay.

11. A method for determining an analyte in a sample comprising the steps of:

(a) introducing a sample to be evaluated into an electrochemical test strip having working and counter electrodes;

(b) applying a potential between the electrodes sufficient to generate a diffusion-limited current when analyte is present in the sample;

(c) dynamically determining a time, t_peak, as the time when diffusion limiting current at the counter electrode is established;

(d) sampling the current after t_peak to collect a plurality of current versus time data points, and analyzing these data points to identify the time when the current is a plateau current having a change of less than 3%/sec, and identifying this time as t_meas, and

(e) generating an indication of analyte in the sample based on the sampled current values at time t_meas.

12. The method of claim 11, wherein the plurality of current versus time points to be sampled is restricted according a range dependent on t_peak.