Determination of organophosphorus and carbamate pesticides using a piezoelectric biosensor

A biosensor based on the quartz crystal microbalance has been developed for the determination of organophosphorus and carbamate pesticides. Detection is based on the inhibitory effects of these compounds on the activity of acetylcholinesterase immobilized on one of the faces of the crystal. Exposure of the immobilized enzyme to a solution of the histological substrate, 3-indolyl acetate, gives rise to the formation of an indigo pigment insoluble product that deposits (precipitates) on the crystal surface. The rate and extent of the enzymatic reaction can be followed in real time by measuring the frequency changes associated with the mass changes at the crystal surface induced by the accumulation of the enzymatic reaction product (indigo pigment). The presence of paroxon (organophosphorus pesticide) or carbaryl (carbamate pesticide) is detected by a diminution of the signal (frequency change) arising from their inhibitory effects. Calibration curves were constructed by plotting the percentage of inhibition vs the logarithm of the pesticide concentration. Detection limits of 5.0 x 10(-8) and 1.0 x 10(-7) M were obtained for paroxon and (after a 5-min preincubation) carbaryl, respectively.