TOWARDS AN IMPLANTABLE AND REFILLABLE GLUCOSE SENSOR-BASED ON OXYGEN-ELECTRODE PRINCIPLES

A glucose biosensor based on an amperometric oxygen electrode has been developed. The properties of oxygen-permeable membranes prepared by d ip-coating the oxygen electrode in silastic materials have been compar ed with those using a standard PTFE mechanically attached membrane. Gl ucose diffusion membranes of different thicknesses also made from sila stic layers have been studied in order to optimize the sensor paramete rs: response time, sensitivity and the concentration range of linear r esponse. The sensor utilizing silicon water-based elastomer (Dow Corni ng 3-5025) for preparation of both oxygen and glucose membranes demons trates a linearity up to 330 mg/dl glucose and a response time of abou t 10 min. The enzyme in the sensor, glucose oxidase, can be replaced ( the sensor refilled) without surgical removal of the sensor from the p atient. Refilling of the sensor is achieved by injecting fresh immobil ized enzyme into the sensor using a septum. A special technique for im mobilization of the enzyme on ultra-low-temperature isotropic (ULTI) c arbon powder held in a liquid suspension has been developed. Prelimina ry studies of the sensors for long-term stability, carried out as a co ntinuous operational test in 100 mg/dl glucose, show practically const ant sensitivity of the sensor (an average value of 0.0548 +/- 0.0049 m uA per 100 mg/dl) over two months of continuous operation. During this period the sensor was refilled three times.