A TELEMETRY-INSTRUMENTATION SYSTEM FOR LONG-TERM IMPLANTABLE GLUCOSE AND OXYGEN SENSORS

This paper describes the development of a compact, low power, implanta ble system for in vivo monitoring of oxygen and glucose concentrations . The telemetry-instrumentation system consists of two amperometric se nsors: one oxygen and one glucose biosensor and two potentiostats for biasing the sensors, an instrumentation amplifier to subtract and ampl ify sensor output signals, and a signal transmitter subunit to convert and transmit glucose dependent signal from the sensors to a remote da ta acquisition system. The system produces a unipolar glucose dependen t voltage in the range of 1 to 3.6 V which is converted to a frequency and then transmitted using a frequency-modulated (FM) oscillator. Ini tial tests were performed on an open model electronic circuit using re sistors to simulate sensor outputs in the 10 to 1000 nA range. Further in vitro evaluation of the system was conducted with a compact printe d circuit board embedded in silicone elastomer, entirely submerged in buffer solution using actual sensors. The test results indicated satis factory operation of the system in simulated implantation conditions f or seven days. Response curve of transmitted signal vs glucose concent ration was obtained. The results of the in vitro evaluation of the tel emetry system permits its subcutaneous implantation in an animal model .