A POTENTIOMETRIC BIOSENSOR FOR PESTICIDES BASED ON THE THIOCHOLINE HEXACYANOFERRATE(III) REACTION

A solid-state acetylcholinesterase (AChE) sensor was developed on the basis of AChE acetylthiocholine-hexacyanoferrate (III) reaction. Various properties of the sensor were investigated and possibilities for its practical use in the detection and assay of pesticides are suggested. The response of the sensor was induced by two phenomena: the Donnan effect and the redox potential. Unlike pH-sensitive sensors, this type of sensor is operated at high ionic strength and a high buffer capacity. The ability of the AChE sensor to assay pesticides was demonstrated by the characterization and quantitative determination of dichlorvos based on its inhibition of AChE. The kinetics of inhibition by dichlorvos of the reaction with AChE were studied by potentiometric and photometric methods. The bimolecular reaction constant was 7.07 10(5) M-1 min-1 and the affinity constant was 4.76 10(-6) M. The detection limits for dichlorvos were 1 muM for a flow-injection mode and 0.2 muM for stationary measurement. The AChE acetylthiocholine-hexacyanoferrate(III) system opens up possibilities for the detection and assay of toxic chemicals by the use not only potentiometric but also of other types of sensors.