Glucose Biosensor Based on Oxygen Electrode. Part II: Long-Term Operational Stability of the Rechargeable Glucose Biosensor

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Abstract
A potentially implantable glucose biosensor for measuring blood or tissue glucose levels in diabetic patients has been developed. The glucose biosensor is based on an amperometric oxygen electrode and immobilized glucose oxidase enzyme, in which the immobilized enzyme can be replaced (the sensor recharged) without surgical removal of the sensor from the patient. Recharging of the sensor is achieved by injecting fresh immobilized enzyme into the sensor using a septum. A special technique for immobilization of the enzyme on Ultra-Low Temperature Isotropic (ULTI) carbon powder held in a liquid suspension has been developed. In vitro studies of the sensors show stable performance during several recharge cycles over a period of 3 months of continuous operation. Diffusion membranes which ensure linear dependence of the sensor response on glucose concentration have been developed. These membranes comprise silastic latex-rubber coatings over a microporous polycarbonate membrane. Calibration curves of the amperometric signal show linearity over a wide range of glucose concentrations (up to 16 mM), covering hypoglycemic, normoglycemic and hyperglycemic conditions. The experimental results confirm the suitability of the sensors for in vitro measurements in undiluted human sera.