Investigations of potentially implantable glucose sensors

Abstract

The catalytic oxidation of H2 02 on Pt and Pt/Ir electrodes in pH 7.4 phosphate buffer was studied. It was found that the electron transfer reaction is more favorable at low concentration and at a well stabilized Pt /Ir electrode the dynamic range can be extended to nearly 1 mM. The oxidation of H20i is independent of oxygen partial pressure. The electrode surface conditioning was proven to be the most important factor affecting the quantitative measurement of H20i. Covering the electrode surface with cellulose acetate membrane could effectively protect the electrode surface and substantially shorten the stabilization time.

A needle-type miniature glucose sensor for in vivo monitoring was developed. Its performance was evaluated both in vitro and in vivo. A multi-layer inner .membrane was demonstrated to successfully eliminate electrochemical interferences. The in vivo interference from acetaminophen has been reduced to a minimal level. The sensor could be sterilized and stored in dry state without losing its characteristics, which made clinical applications possible.

A method of sensor toxicity screening was developed using cell culture technique. A freshly prepared sensor was found to have certain toxicity. The toxic substances could be removed by buffer treatment and a non toxic sensor was readily available.

To evaluate the effect of oxygen on the performance of the glucose sensor, a miniature oxygen sensor was constructed which had identical size and geometry to those of the glucose sensor. It was characterized in buffer and in vivo measurements were carried out in rat subcutaneous tissue. Results showed that glucose sensors of low sensitivity were essentially independent of environmental Po2 while high sensitivity sensors were affected by oxygen fluctuation