Development of potentially implantable glucose sensors.

Abstract

A novel glucose oxidase based needle-type glucose microsensor has been developed for subcutaneous glucose monitoring. The new configuration greatly facilitates the deposition of uniform enzyme and polymer films so that sensors with satisfactory in vitro characteristics (upper limit of linear range (>15 mM) and response time (<5 min) can be prepared in high yield (>60%). The sensor is equivalent in size to a 26 gauge needle (0.45 mm o.d.) and can be implanted with ease without any incision. The insertion of the sensor causes minimal trauma to the tissue and to the sensor itself. The multilayer structure of the sensor ensures satisfactory performance in subcutaneous tissue over extended periods of time (up to 20 days). The sensor response is largely independent of oxygen tension in the normal physiological range. It also exhibits the desired sensitivity and selectivity. A two-point in vivo calibration procedure is adapted for in vivo evaluation of the sensors. Both short-term and long-term implantation experiments are described. The methods of cell culture toxicity testing are modified and applied to locate the source of toxicity in a multi-component glucose sensor. It is shown that a non-toxic sensor can be readily obtained by removing the leachable toxic substances through extraction in phosphate buffer. A nonenzymatic glucose sensor that utilizes permselective membranes to achieve the selectivity required for screening glucose in biological fluids has been described. Interference from endogenous oxidizable substances such as amino acids, urea, ascorbic acid, and uric acid, as well as the effect of chloride and proteins on glucose response, is studied by using flow injection analysis. A set of membranes made of Nafion perfluorinated membrane and collagen, when arranged in front of the working electrode (gold), result in significant improvement in the system selectivity and sensitivity.