EVALUATION OF THE USE OF FREE AND IMMOBILIZED ACETYLCHOLINESTERASE FOR PARAOXON DETECTION WITH AN AMPEROMETRIC CHOLINE OXIDASE BASED BIOSENSOR

Aspects related to the use of free and immobilised acetylcholinesteras e (AChE) for the development of an amperometric biosensor for organoph osphorus (OF) insecticides based on enzyme inhibition have been studie d. Procedures based on free and immobilised AChE were previously studi ed from many authors but the measurement of the residual enzyme activi ty has been directly carried out in the same sample where incubation o f AChE with OP has been performed. With AChE immobilised on a nylon ne t 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 performe d in a standard solution containing the specific substrate in the buff er. With this two-step procedure, a Pt electrode, only covered with a thin layer of cross-linked choline oxidase and without any membrane, h as also been used in batch conditions obtaining interesting results in terms of sensitivity, precision and limit of detection.