CAPACITANCE DETECTION IN ELECTROCHEMICAL ASSAYS

1 . A method of determining capacitance of a biosensor chamber having a 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.

2 . The method of claim 1 , in which the calculating comprises calculating capacitance with an equation of the form:

C =|( i T sinΦ)|÷2 πƒV

where:

C≈capacitance;

i T ≈total current;

Φ≈phase angle between total current and resistor current;

ƒ≈frequency; and

V≈voltage.

3 . The method of claim 2 , in which the calculating 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.

4 . The method of claim 3 , 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.

5 . The method of claim 4 , 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.

6 . The method of claim 5 , in which the subtracting further comprises calculating an average of the first and second angles.

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

8 . An analyte measurement system comprising:

An analyte test strip including:

a substrate having a reagent disposed thereon;

at least two electrodes proximate the reagent in test chamber;

an analyte meter including:

a strip port connector disposed to connect to the two electrodes;

a power supply; and

a microcontroller electrically coupled to the strip port connector and the power supply, the microcontroller being programmed to:

(a) initiate an electrochemical reaction in the biosensor chamber; apply an oscillating voltage of a predetermined frequency to the chamber;

(b) determine a phase angle between a current output and the oscillating voltage from the chamber; and

(c) calculate 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.

9 . An analyte measurement system comprising:

An analyte test strip including:

a substrate having a reagent disposed thereon;

at least two electrodes proximate the reagent in test chamber;

an analyte meter including:

a strip port connector disposed to connect to the two electrodes;

a power supply; and

a microcontroller electrically coupled to the strip port connector and the power supply such that a percent error in capacitance measurement of the test strip across a range of capacitance as compared to a referential parallel R-C circuit is less than about 3%.