Quartz crystal microbalance determination of organophosphorus and carbamate pesticides

We have developed a quartz crystal microbalance (QCM) biosensor for the determination of organophosphorus and carbamate pesticides. A change in resonant frequency is observed as a result of mass adsorption, and we have used this as the basis for sensor development. Specifically, we have used a two-enzyme system (acetylcholine-esterase and choline oxidase) which converts acetylcholine to betaine producing hydrogen peroxide as a by-product. In a third enzyme reaction (peroxidase), the peroxide is able to oxidise benzidines (3,3′-diaminobenzidine) into an insoluble product that precipitates out and can adsorb to surfaces. Non-ionic surfactants have been used for the first time to enhance the surface deposition of suspended precipitate, thereby improving sensor sensitivity. Pesticides are known to inhibit esterase activity (thereby reducing the amount of QCM-detectable precipitate produced). We have shown that the QCM-enzyme sensor system can be used to determine carbaryl and dichlorvos down to 1 ppm.