High sensitive bienzymic sensor for the detection of dithiocarbamate fungicides

A bienzymic sensor for the determination of dithiocarbamate fungicides was developed based on aldehyde dehydrogenase inhibition. The NADH formed by the oxidation of propionaldehyde by aldehyde dehydrogenase was reoxidised by diaphorase using hexacyanoferrate(III) as electron acceptor. The hexacyanoferrate(II) produced was electrochemically oxidised at a potential of 250 mV vs. SCE. As dithiocarbamate fungicides inhibit aldehyde dehydrogenase, a decrease of the induced current was correlated to their concentration in the working medium. Aldehyde dehydrogenase and diaphorase were used in solution or entrapped in a photocrosslinkable poly(vinyl alcohol) bearing styrylpyridinium groups. The best results were achieved using entrapped enzymes and the sensitivity of the sensor was improved by lowering the amount of enzyme and by increasing the contact time between the pesticide and the enzyme. Using entrapped enzymes, the detection of 1.48 ppb of maneb was achieved whereas the commonly used spectrophotometric method allows to detect only 400 ppb of dithiocarbamate.