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 chel ate (Ni-NTA silica). This sensor was used to detect the inhibitory effects of organophosphorus and carbamate pesticides on acetylcholinesterase activi ty. The immobilisation method takes advantages of the ability of Ni2+ to bi nd to peptides or proteins containing histidine residues. The only requirem ent 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 geneti c engineering: to incorporate six histidine tails. With the optimised proce dure described, a good sensor stability and a high sensitivity were obtaine d. The sensor was tested for the detection of the pesticides paraoxon, dich lorvos and chlorpyrifos ethyl oxon, the defection level being respectively 4.1, 0.5 and 0.1 ppb.