ABSTRACT
An enzyme electrode is the first type of biosensor which has been proposed and which results from the association of an enzyme and an electrochemical sensor which can detect a reactant involved in a catalyzed reaction. The enzyme may be soluble, immobilized onto a membrane, or embedded in a thin layer, but in each case it is tightly maintained in close contact with the electrochemical transducer. When the enzyme is in the presence of its substrate (i.e., the target analyte to be monitored in the complex mixture), an electrical signal is obtained that can be correlated to its concentration. Potentiometric and amperometric electrodes are commonly used as basic sensors; the potential or current output is then related to the analyte concentration with a logarithmic or linear relationship, respectively. A strong interest arose for such analytical devices and numerous papers appeared in the literature. Excellent reviews dealing with both theoretical and analytical aspects of the various types of enzyme electrodes have been published. 1-6 In this chapter we restrict the discussion to amperometric enzyme electrodes, with emphasis on membrane systems and characteristics for the practical use of such biosensors as detection limit, dynamic linear range, lifetime, and number of assays performed with the same membrane.
