AN ISFET GLUCOSE SENSOR WITH A SILICONE-RUBBER MEMBRANE FOR UNDILUTED SERUM MONITORING

An ion-sensitive field-effect transistor (ISFET) glucose sensor with a silicone rubber membrane has been fabricated and its operation has been demonstrated in monitoring glucose concentration in serum and suction effusion fluid without dilution. The sensor characteristics are evaluated by measuring glucose concentrations in HEPES-NaOH buffers with different buffer capacities. The silicone membrane, which restricts glucose diffusion, expands the linear calibration range up to 500 mg/dl glucose. This membrane also restricts buffer species diffusion, so that the sensor output is not affected by solution buffer capacity. Moreover, investigation on the relationship between the sensor response and dissolved oxygen concentration shows that this sensor maintains constant outputs in solutions containing 1.5-7.5 ppm of oxygen. The sensor is mounted in a flow cell, into which serum samples and HEPES-NaOH buffer solution are alternately fed by a peristaltic pump. It takes 15 min to measure one sample. In 21 measurements on the same serum sample, the sensor output variance coefficient is found to be 4.7%. The sensor is applied to monitor glucose concentration in glucose-loaded rabbit suction effusion fluid. The glucose-level profile obtained by this sensor shows a good correlation with that measured by a conventional glucose analyser.