Capacitance detection in electrochemical assay

• US 9,645,104 B2
• Filed: 04/07/2014
• Issued: 05/09/2017
• Est. Priority Date: 02/25/2010
• Status: Expired due to Fees

• Current Assignee: Cilag Gmbh International (Johnson & Johnson)
• Original Assignee: LifeScan Scotland Limited (Johnson & Johnson)
• Inventors: Elder, David, Rippel, Sven
• Primary Examiner(s): Nguyen, Vincent Q
• Application Number:
  US14/246,592
• Publication Number:
  US 20140332415A1
• Time in Patent Office: 1,128 Days
• Field of Search: 324658-690
• CPC Class Codes: G01N 27/22 by investigating capacitance
• CPC Class Codes: G01N 27/307 Disposable laminated or multilayered electrodes G01N27/3272 takes precedence
• CPC Class Codes: G01N 27/3274 Corrective measures, e.g. error detection, compensation for temperature or hematocrit, calibration coding of calibration information G01N33/48771

Abstract

A method and system are provided to determine fill sufficiency of a biosensor test chamber by determining capacitance of the test chamber in which an electrochemical reaction is initiated in the test chamber and an oscillating voltage of a predetermined frequency is applied to the chamber. A phase angle between a current output and the oscillating voltage from the chamber is determined and the capacitance is calculated based on a product of the current output and a sine of the phase angle divided by a product of two times pi times the frequency and the voltage.

Claims

1. A method of determining capacitance of a biosensor chamber having two electrodes disposed in the chamber and coupled to a microcontroller, the method comprising:

initiating an electrochemical reaction in the biosensor chamber;

applying an oscillating voltage of a predetermined frequency to the chamber;

determining a phase angle between a current output and the oscillating voltage from the chamber; and

calculating a capacitance of the chamber based on a product of the current output and a sine of the phase angle divided by a product of two times pi times the frequency and the voltage, and wherein the calculating comprises calculating capacitance with an equation of the form;

C=|(i_T sin Φ

)|÷

2π

fV

where;

C≈

capacitance;

i_T≈

total current;

Φ

≈

phase angle between total current and resistor current;

f≈

frequency; and

V≈

voltage

and in which the calculating further comprises;

sampling a plurality of current outputs from the chamber over one cycle of the frequency;

obtaining a mean of sampled current output;

subtracting the mean from each sampled current of the plurality of current outputs; and

extracting root-mean-squared value of all negative values from the subtracting to provide for the total current output.

2. The method of claim 1, in which the calculating comprises:

determining from the sampling, at least one cross-over point of the current from negative to positive values; and

interpolating proximate the at least one cross-over point of the current to determine a first angle at which the current changes from positive to negative or negative to positive.

3. The method of claim 2, in which the interpolating the at least one cross-over point of the current comprises:

interpolating another cross-over point from the sampling to determine another angle at which the current changes from positive to negative or negative to positive; and

subtracting from the another angle approximately 180 degrees to provide for a second angle.

4. The method of claim 3, in which the subtracting further comprises calculating an average of the first and second angles.

5. The method of claim 3, in which the calculating comprises determining a difference in the angle between the oscillating input current and the output current as the phase angle.