An enzyme-based sensor for glucose was first employed by LC Clark and C Lyons in 1962. More recent applications involve enzymes which catalyse redox reactions whose rates are made proportional to the analyte (substrate) concentration. Typically the progress of the reaction is monitored by measuring the rate of formation of a product or the disappearance of a reactant. If a product or reactant is electroactive, then its concentration may be monitored directly.
The enzymes catalysing these reactions are typically oxidoreductases, but hydrolytic enzymes such as alkaline phosphatase can also be used if they produce an electroactive species.
"Biosensors - A Practical Approach", Cass AEG (Ed.) OUP (1990) FIZ610.28
Clark LC, Lyons C, (1962) Ann.N.Y.Acad.Sci.102, 29.