Insecticide identification using a flow injection analysis system with biosensors based on various cholinesterases

This work presents an automatic method able to identify the presence of neurotoxic insecticides using omethoate as a model compound. The acetylcholinesterase (AChE)-based biosensors used to detect the neurotoxic insecticides present two shortcomings: the weak limit of detection (LOD) and the lack of selectivity. An appropriate LOD is obtained in our work by using two sensitive AChEs from Drosophila melanogaster (Dm): the wild type (wt-Dm) and the E69W mutant. To discriminate between the insecticides and all other interferences, we use a FIA system that provides analytical information acquired from two enzymes: (i) the sensitive Dm-AChEs and (ii) an omethoate-resistant AChE from Electric Eel (Eel), which is equally affected by the matrix. The enzymes were immobilised on screen-printed electrodes by entrapment in a photocrosslinkable PVA-SbQ polymer used with a FIA system with three channels, each one of them simultaneously analysing the same sample using biosensors based on different AChEs. The biosensor based on the wt-Dm had a LOD of 2 × 10−6 M omethoate, while the one based on the E69W mutant permitted to lower the LOD to 1 × 10−7 M. Interferences produced by mercury and hypocloryte were successfully discriminated. Environmental water samples were also analysed.