CHARACTERIZATION IN-VITRO OF A NAPHTHOQUINONE-MEDIATED GLUCOSE OXIDASE-MODIFIED CARBON-PASTE ELECTRODE DESIGNED FOR NEUROCHEMICAL ANALYSIS IN-VIVO

We have constructed and characterised in vitro a glucose sensor using glucose oxidase (GOx) incorporated onto the surface of a 200-mu m diam eter carbon paste electrode containing 1,4-naphthoquinone that acted a s a mediator for electron transfer. The rationale behind this design w as to produce a biosensor with minimal ascorbate and oxygen interferen ce for use in neurochemical analysis in vivo. The key to successful re alisation of this aim was detailed investigation of the optimum potent ial for operating the electrode. An applied potential of between - 100 and - 160 mV vs. see was found to produce the best selectivity for gl ucose; lower values gave faradaic currents for oxygen, and higher pote ntials faradaic responses for ascorbate. Operating at - 160mV, the sen sor had the following advantages: good sensitivity (ca. 20 mu A cm(-2) for 5 mM glucose); insensitivity to competition for reduced enzyme by oxygen; and freedom from lipid surfactant interactions. The stability of the electrode was limited, however, to a few days.