A capacitive field-effect sensor for the direct determination of organophosphorus pesticides

A novel capacitive field-effect sensor for the direct determination of organophosphorus pesticides by the enzyme organophosphorus hydrolase (OPH) is presented. The enzyme OPH hydrolyses organophosphorus compounds catalytically, thus releasing H+ ions. By means of a silicon-based field-effect sensor, which consists of a layer sequence of Al/p-Si/SiO2 with alternative pH-sensitive materials (Ta2O5, Al2O3 and Si3N4), this pH shift can be recorded directly in a potentiometric measuring arrangement. To obtain the enzyme biosensor, thus the OPH has been immobilised on top of the pH-sensitive layer structure. Typical sensor characteristics, like pH sensitivity, sensitivity towards paraoxon, reversibility of the sensor signal, response time, detection limit, long-term stability and selectivity to various pesticides have been studied.