Development of a needle-type glucose sensor based on a titanium dioxide oxygen electrode for the artificial pancreas

A needle-type glucose sensor has been developed using a new type of oxygen (O 2 ) electrode system composed of a 0.5 or 1.0 mm Ti wire about 2.5 mm in diameter and 35 mm long, whose top is anodically oxidized. It responds well to O 2 tension in a saline solution. As the residual current of the prototype sensor is rather large at zero O 2 tension, the oxidized surface has been modified with Pt by electroplating. Thus the O 2 reduction preferentially proceeds on the Pt sites, and the applied potential for the sensor becomes less negative than for the prototype. Miniaturization of the sensor has been performed by using the side wall of the 0.3 mm Ti wire ≈ 1.1 mm in diameter and 15 mm long as the sensing and enzyme immobilizing site. GOD is immobilized on the Pt-modified surface of the Ti electrode with a silanizer using glutaraldehyde and BSA, or with an electropolymerized polypyrrole film. Both sensors linearly respond to glucose over a range of more than 500 mg/dl. The shape of the miniature sensor is promising for immobilizing the enzyme and coating the membranes easily.