1.4. Origin of Biosensor

Enzyme Electrode. The biosensor was first described by Clark and Lyons in 1962, when the term enzyme-electrode was adopted. In this first enzyme electrode, an oxido-reductase enzyme, glucose oxidase, was held next to a platinum electrode in a membrane sandwich (Fig. 1.8) . The platinum anode polarized at + 0.6 V responded to the peroxide produced by the enzyme reaction with substrate. The primary target substrate for this system was glucose:

and led to the development of the first glucose analyser for the measurement of glucose in whole blood. This Yellow Springs Instrument (Model 23 YSI) appeared on the market in 1974, and the same technique as employed here has been applied to many other oxygen mediated oxido-reductase enzyme systems.

Use of Membrane for Selectivity. A key development in the YSI sensor was the employment of membrane technology in order to eliminate interference by other electro-active substances. Polarized at +0.6V, the major interference to the peroxide measurement is ascorbic acid. Various combinations of membrane-enzyme sandwich have been developed, all satisfying the following criteria:

This was accomplished in the YSI, for example, with an enzyme layer sandwiched between a cellulose acetate membrane and a Nucleopore polycarbonate membrane.