Measurement of Glucose Concentration in the Presence of Coreactants with a Platinum Electrode

An implantable glucose sensor is being developed that is based on the use of a high-area platinum electrode. The sensor is operated in a controlled potential mode, in which the potential of the platinum working electrode versus an unpolarized reference electrode is periodically varied according to a preselected voltage-time regimen. The change in potential is accompanied by a flow of current between the platinum working electrode and a counter-electrode. This current serves to periodically rejuvenate the electrode surface and to provide a signal that is proportional to the glucose concentration. A method for analyzing this signal has been developed, the compensated net charge (CNC) method, that involves integration of the current over one complete potential cycle. This method significantly improves both the sensitivity and selectivity for determining glucose in the presence of the normal physiologic coreactants. For a solution containing glucose, amino acids, and urea, a change in glucose concentration from 50 to 150 mg/dl gives about a 50% change in the net charge. A change in the urea concentration from 20 to 40 mg/dl has no effect on the net charge. A change in the amino acids concentration from 35 to 65 mg/dl has little effect on the net charge above a glucose concentration of about 100 mg/dl. Negligible effects on the net charge have also been found for creatinine (0–1.5 mg/dl) and uric acid (0–4 mg/dl).