GLUCOSE BIOSENSOR BASED ON OXYGEN-ELECTRODE .2. LONG-TERM OPERATIONALSTABILITY OF THE RECHARGEABLE GLUCOSE BIOSENSOR

A potentially implantable glucose biosensor for measuring blood or tis sue glucose levels in diabetic patients has been developed. The glucos e biosensor is based on an amperometric oxygen electrode and immobiliz ed glucose oxidase enzyme, in which the immobilized enzyme can be repl aced (the sensor recharged) without surgical removal of the sensor fro m the patient. Recharging of the sensor is achieved by injecting fresh immobilized enzyme into the sensor using a septum. A special techniqu e for immobilization of the enzyme on Ultra-Low Temperature Isotropic (ULTI) carbon powder held in a liquid suspension has been developed. I n vitro studies of the sensors show stable performance during several recharge cycles over a period of 3 months of continuous operation. Dif fusion membranes which ensure linear dependence of the sensor response on glucose concentration have been developed. These membranes compris e silastic latex-rubber coatings over a microporous polycarbonate memb rane. Calibrution curves of the amperometric signal show linearity ove r a wide range of glucose concentrations (up to 16 mM), covering hypog lycemic, normoglycemic and hyperglycemic conditions. The experimental results confirm the suitability of the sensors for in vitro measuremen ts in undiluted human sera.