AN AMPEROMETRIC GLUCOSE-OXIDASE POLY(O-PHENYLENEDIAMINE) BIOSENSOR FOR MONITORING BRAIN EXTRACELLULAR GLUCOSE - IN-VIVO CHARACTERIZATION INTHE STRIATUM OF FREELY-MOVING RATS/

Amperometric glucose biosensors based on the immobilization of glucose oxidase (GOx) on PI electrodes with electropolymerized o-phenylenedia mine (PPD) were implanted in the right striatum of freely-moving rats. Carbon paste electrodes for the simultaneous monitoring of ascorbic a cid (AA) and/or tissue O-2 were implanted in the left striatum. A deta iled in vivo characterization of the Pt/PPD/GOx signal was carried out using various pharmacological manipulations. Confirmation that the bi osensor responded to changing glucose levels in brain extracellular fl uid (ECF) was obtained by intraperitoneal (i.p.) injection of insulin that caused a decrease in the Pt/PPD/GOx current, and local administio n of glucose (1 mM) via an adjacent microdialysis probe that resulted in an increase in the biosensor current. An insulin induced increase i n tissue O-2 in the brain was also observed. Interference studies invo lved administering AA and subanaesthetic doses of ketamine i.p. Both r esulted in increased extracellular AA levels with ketamine also causin g an increase in O-2. No significant change in the Pt/PPD/GOx current was observed in either case indicating that changes in O-2 and AA, the principal endogenous interferents, have minimal effect on the respons e of these first generation biosensors. Stability tests over a success ive 5-day period revealed no significant change insensitivity. These i n vivo results suggest reliable glucose monitoring in brain ECF. (C) 1 998 Elsevier Science B.V.