Evaluation of the use of free and immobilised acetylcholinesterase for paraoxon detection with an amperometric choline oxidase based biosensor

Aspects related to the use of free and immobilised acetylcholinesterase (AChE) for the development of an amperometric biosensor for organophosphorus (OP) insecticides based on enzyme inhibition have been studied. Procedures based on free and immobilised AChE were previously studied from many authors but the measurement of the residual enzyme activity has been directly carried out in the same sample where incubation of AChE with OP has been performed. With AChE immobilised on a nylon net and not assembled on the sensor it is possible to perform incubation and measurement steps separately: the incubation step is performed in the sample containing the inhibitor, the measurement step is performed in a standard solution containing the specific substrate in the buffer. With this two-step procedure, a Pt electrode, only covered with a thin layer of cross-linked choline oxidase and without any membrane, has also been used in batch conditions obtaining interesting results in terms of sensitivity, precision and limit of detection.