Chapter 14
Amperometric Enzyme Sensors
Amperometry is a suitable transduction method when coupled with an enzymatic reaction involving oxidation/reduction steps, such as those catalyzed by oxidase and dehydrogenase enzymes. The prototype is the amperometric glucose sensor, which was first introduced by Clark and Lyons in 1962 [1], and that was the starting point for further impressive advances and improvements.
During the evolution of the technology of oxidase-based amperometric sensors three main transduction methods were developed. These are summarized below with reference to oxidase-type enzymes. The general scheme for an oxidase-catalyzed reaction is:
(14.1) 
where S an P are the substrate and the product of the enzymatic reaction.
Hence, first-generation amperometric sensors relied on electrochemical monitoring of either oxygen depletion or hydrogen peroxide formation. In second-generation sensors oxygen is replaced by an artificial electron acceptor (that is, a redox mediator) that could be incorporated along with the enzyme in the biocatalytic layer [2]. In this way, the sensor becomes independent of any additional reagent in solution. Attempts at performing direct electron transfer from the enzyme to the electrode led to the third-generation, mediatorless sensors [2]. Current research is directed at improving sensor performance by rational use of new materials, particularly ...
