A Novel Blood Glucose Monitoring Method an ISFET Biosensor Applied to Transcutaneous Effusion Fluid

Quasicontinuous blood glucose monitoring has been achieved by applying an ISFET (ion sensitive field effect transistor) biosensor to transcutaneous effusion fluid. The effusion fluid, collected through the skin by evacuation without harm to a living creature, contains the same glucose and urea concentration as that in the serum (1). The main advantage of using the ISFET biosensor is its application to small volume samples; for example, only about 0.4 µl/min effusion fluid, under 400 torr suction, was extracted from a 1 cm² skin surface in a rabbit experiment. The ISFET biosensor, which was employed for this glucose measurement, is 1.6 mm wide, 8 mm long and 0.35 mm thick. By using an effusion fluid collection cell 8 cm² in area, the fluid was collected every 10 min. Glucose concentrations for every 10 µl of sampling fluid were measured by the ISFET biosensor and compared with blood glucose concentration monitored by a continuous glucose analyzer. By injecting glucose solution into a femoral vein, an artificial high glucose concentration was induced. A good correlation between effusion fluid glucose concentration measured by a biosensor and blood glucose concentration measured by continuous monitoring equipment was obtained.