Patent ID: 8163164

Claim:
A method for determining a concentration of an analyte in a sample, comprising the steps of: contacting a sample with a sensor, wherein the sensor comprises: a working electrode and a counter electrode, wherein the working electrode and counter electrode are separated by an effective distance in a range of 25 to 1000 μm; a sample chamber for holding the sample fluid, the sample chamber comprising the working electrode, the counter electrode, a first indicator electrode to indicate when the sample chamber is beginning to fill with sample, and a second indicator electrode to indicate when the sample chamber is substantially filled with sample, wherein the sample chamber is sized to contain a volume of no more than about 1 μL of the sample; and an analyte-responsive enzyme and a diffusible redox mediator disposed in the sample chamber, which redox mediator is non-immobilized wherein a background signal generated by the diffusible redox mediator in the absence of the analyte is no more than 25% of the signal generated by oxidation or reduction of the average normal physiological amount of analyte; observing a signal from the first indicator electrode to signify that the sample chamber is beginning to fill with sample; observing a signal from the second indicator electrode to signify that the sample chamber is substantially filled with sample; generating a sensor signal at the working electrode, and determining the concentration of the analyte by coulometry using the sensor signal.