Implanted electroenzymatic glucose sensors

The advent of electrochemical sensors for intermittent sampling of blood gases and hydrogen ions in the clinic, intensive care, and surgical units has revolutionized diagnostic and critical care medical technics. The use of electrochemical sensors for continuous transcutaneous monitoring of blood gases is further enhancing the medical surveillance of patients. The more recent introduction of glucose and other electroenzymatic sensors has stimulated broad research in the development of metabolic monitoring. For the present research, the glucose sensor widely used for the rapid specific micro-analysis of whole blood and plasma is explored for possible use as an in vivo intravascular or tissue-implanted sensor. This sensor is based on the polarographic measurement of hydrogen peroxide generated by glucose oxidase (EC 1.1.3.4) held between two membranes. The first membrane allows the diffusion of glucose, ions, and many other small molecules, while the second membrane allows the diffusion of the glucose-generated hydrogen peroxide to the platinum surface, but excludes ascorbic acid, bilirubin, and uric acid. Such sensors respond rapidly and specifically when acutely implanted subcutaneously in cats and dogs. They function well as glucose-sensor-tipped venous catheters. One sensor was repeatedly used for in vitro polarograms, subcutaneous and blood glucose monitoring, over a period of ten months, with storage in the cold between uses, with the complete retention of its response characteristics.