IMMOBILIZATION OF ENZYMES ON SCREEN-PRINTED SENSORS VIA AN HISTIDINE TAIL. APPLICATION TO THE DETECTION OF PESTICIDES USING MODIFIED CHOLINESTERASE

A new screen-printed electrode for the detection of pesticides is described based on the immobilisation of acetylcholinesterase (AChE) by a metal chelate (Ni-NTA silica). This sensor was used to detect the inhibitory effects of organophosphorus and carbamate pesticides on acetylcholinesterase activity. The immobilisation method takes advantages of the ability of Ni2 + to bind to peptides or proteins containing histidine residues. The only requirement for this immobilisation to occur using a metal chelate is the presence of a histidine tail on the enzyme molecule. The AChE was modified by genetic engineering to incorporate six histidine tails. With the optimised procedure described, a good sensor stability and a high sensitivity were obtained. The sensor was tested for the detection of the pesticides paraoxon, dichlorvos and chlorpyrifos ethyl oxon, the detection level being respectively 4.1, 0.5 and 0.1 ppb.