DIRECT ELECTRON-TRANSFER BASED TRI-ENZYME ELECTRODE FOR MONITORING OFORGANOPHOSPHORUS PESTICIDES

A potentiometric biosensor has been developed based on the ability of organophosphorus pesticides to inhibit the catalytic activity of the e nzyme choline esterase. The detection of choline esterase activity is based on the principle of molecular transduction. Immobilized peroxida se acting as the molecular transducer, catalyzes the electroreduction of hydrogen peroxide by direct (mediatorless) electron transfer. The s ensing element consists of a carbon based electrode covered by a layer of three co-immobilized enzymes: choline esterase, choline oxidase an d peroxidase. A butyryl choline sensitive tri-enzyme electrode has bee n developed employing highly dispersed teflonized carbon black as an e lectrode material. The immobilization procedure is based on physical a dsorption of peroxidase and co-immobilization of choline oxidase and c holine esterase using glutaraldehyde as a binding agent. The electrode retains 95% of its initial activity after 1 month of storage at 4 deg rees. The parameters of the inhibitor assay procedure have been optimi zed. The procedure for measuring the electrode activity requires 3-5 m in. Incubation of the electrode in a solution containing the organopho sphorus pesticide, trichlorfon, for 10 min results in a notable decrea se of electrode activity. This allows for the determination of trichlo rfon in a nanomolar concentration range with a low detection limit of 5 nM (1.3 ppb).