Capacitance detection in electrochemical assay

Patent metadata

Field	Value
Publication number	US-9645104-B2
Application number	US-201414246592-A
Country	US
Kind code	B2
Filing date	Apr 7, 2014
Priority date	Feb 25, 2010
Publication date	May 9, 2017
Grant date	May 9, 2017

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.

First claim

What is claimed is:

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.

Assignees

• Lifescan Scotland Ltd

Inventors

• Elder David
• Rippel Sven

Classifications

• G01N27/22 Primary

  by investigating capacitance · CPC title

• G01N27/307 Primary

  Disposable laminated or multilayered electrodes (G01N27/3272 takes precedence) · CPC title

• G01N27/3274 Primary

  Corrective measures, e.g. error detection, compensation for temperature or hematocrit, calibration (coding of calibration information G01N33/48771) · CPC title

• G01N27/416

  Systems (G01N27/27 takes precedence) · CPC title

• G01N33/487

  of liquid biological material · CPC title