A SIMPLE DISPOSABLE POTENTIOMETRIC BIOSENSOR FOR PESTICIDES

Organophosphorus pesticides can imitate the molecular shape of choline esters and they can therefore bind irreversibly to the esteratic acti ve sites of cholinesterases. In the study reported on here this enzyme inhibition has been investigated as a basis for the determination of pesticides by potentiometry, with an internal pH electrode detecting t he change in proton concentration arising from the formation of acid i n the reaction catalysed by the enzyme. Various methods for the immobi lization of butyryl cholinesterase on the surface of the pH electrode have been investigated, and a disposable biosensor based on thermally grown iridium oxide electrodes with a simple procedure for immobilizat ion of the enzyme is described. Indirect determination at the level of mu g ml(-1) of a model pesticide, paraoxon, can be successfully achie ved using the irreversible inhibition of the enzyme.