THE RESPONSE OF SCREEN-PRINTED ENZYME ELECTRODES CONTAINING CHOLINESTERASES TO ORGANO-PHOSPHATES IN SOLUTION AND FROM COMMERCIAL FORMULATIONS

Electrodes containing a layer of cobalt phthalocyanine, mixed with gra phite ink, and a layer of acetyl-or butyryl cholinesterase were constr ucted by screen-printing, except for a thin layer of polyurethane appl ied by an airbrush. When the electrodes were made the anodes of electr ochemical cells, the generation of current by the addition of enzyme s ubstrate was inhibited by standard solutions of organo-phosphate pesti cides. Cholinesterase activity was inhibited by paraoxon and dichlorvo s concentrations as low as 10(-8) M. The relationship between the loga rithm of concentration and the inhibition quotient (ratio between init ial current and the rate of change of the inhibited current) was curvi linear. Malathion only caused an inhibition of current generated by el ectrodes containing acetyl cholinesterase. Inhibition by malathion req uired a period of pre-incubation in the pesticide before addition of e nzyme substrate, and was evident down to, and including, a concentrati on of 10(-7) M. The addition of diluted commercial formulations of som e organo-phosphate pesticides caused rapid inhibition of electrode fun ction. Nearly linear relationships were observed between the logarithm of the degree of dilution of commercial formulations containing P=O g roups and the natural logarithms of the inhibition quotients. Inhibiti on by formulations containing malathion did not require pre-incubation of the electrodes in the mixture (only electrodes containing acetyl c holinesterase were tested). The relationship between the logarithm of the degree of dilution and the natural logarithm of the inhibition quo tient was curvilinear. The responses of the screen-printed electrodes to commercial formulations of pesticides indicate that they may be a s uitable platform for further development of sensors capable of detecti ng the presence of these pesticides in the environment. (C) 1997 Elsev ier Science Limited.