The Low-Potential Approach of Glucose Sensing

Study of glucose sensing using a smooth Pt electrode and cyclic voltammetry (CV) at low potentials revealed two well-defined, redox current peaks of adsorbed species. At 370 C a reduction peak occurs at ¿0.80 V versus Ag/AgCl and an oxidation peak at ¿0.72 V. Furthermore, the redox couple has been shown to be reversible, involving a simple, direct, electron-transfer process under diffusion control. The reaction is not complicated by secondary chemical (nonelectro-chemical) reactions. Based on this approach, a square wave voltammetry (SWV) technique has been adopted to obtain pure faradaic currents (noncapacitance current), fast response times, and enhanced sensitivity-for the designated reversible redox peaks. The SWV technique also permits the employment of much smaller-sized Pt wire electrodes (0.5 mm diameter) for glucose sensing. Plots of current versus glucose concentration in Krebs-Ringer solutions, for both redox peaks, are linear for glucose levels in the 70-350 mg/dl range. Studies of glucose concentration variations in the ultrafiltrate of human serum have also demonstrated a linear relationship between current and glucose level. Thus far, the linearity is limited to a narrow glucose range (80¿180 mg/dl), but this is within the critical domain for diabetic control. The advantages of the low-potential approach using SWV is an improvement over CV and could be a promising method for implantable microelectrode glucose sensing.