Acetylcholinesterase-based biosensor electrodes for organophosphate pesticide detection. I. Modification of carbon surface for immobilization of acetylcholinesterase.

Screen-printed carbon electrodes modified with the dialdehydes, glutaraldehyde and terephthaldicarboxaldehyde, and then polyethyleneimine have been utilized for production of pesticide biosensors based on acetylcholinesterase. To improve the extent of dialdehyde modification, the electrodes were NH2-derivatized, initially by electrochemical reduction of 4-nitrobenzenediazonium to a nitroaryl radical permitting attachment to the carbon surface. Subsequent reduction of the 4-nitrobenzene yields a 4-aminobenzene modified carbon surface. Drosophila melanogaster acetylcholinesterase was immobilized either covalently onto dialdehyde modified electrodes or non-covalently onto polyethyleneimine modified electrodes. Internal diffusion limitations due to the dialdehyde and polyethyleneimine modifications increased the apparent Km of the immobilized enzyme. The thiocholine sensitivity was about 90% for dialdehyde modified electrodes and about 10% for polyethyleneimine modified electrodes as compared with non-modified carbon electrodes. The detection limit of the biosensors produced by non-covalent immobilization of acetylcholinesterase onto polyethyleneimine modified carbon electrodes was found to be about 10(-10) M for the organophosphate pesticide dichlorvos.