Nowadays extensive volumes of pesticides are employed for agricultural and\nenvironmental practices, but they have negative effects on human health. The levels of\npesticides are necessarily restricted by international regulatory agencies, thus rapid,\ncost-effective and in-field analysis of pesticides is an important issue. In the present work,\nwe propose a butyrylcholinesterase (BChE)-based biosensor embedded in a flow system for\norganophosphorus pesticide detection. The BChE was immobilized by cross-linking on a\nscreen-printed electrode modified with Prussian Blue Nanoparticles. The detection of\nparaoxon (an organophosphorus pesticide) was carried out evaluating its inhibitory effect on\nBChE, and quantifying the enzymatic hydrolysis of butyrylthiocholine before and after the\nexposure of the biosensor to paraoxon, by measuring the thiocholine product at a working\nvoltage of +200 mV. The operating conditions of the flow system were optimized. A flow\nrate of 0.25 mL/min was exploited for inhibition steps, while a 0.12 mL/min flow rate was\nused for substrate measurement. A substrate concentration of 5 mM and an incubation time\nof 10 min allowed a detection limit of 1 ppb of paraoxon (corresponding to 10% inhibition). The stability of the probe in working conditions was investigated for at least eight\nmeasurements, and the storage stability was evaluated up to 60 days at room temperature in\ndry condition. The analytical system was then challenged in drinking, river and lake water\nsamples. Matrix effect was minimized by using a dilution step (1:4 v/v) in flow analysis. This\nbiosensor, embedded in a flow system, showed the possibility to detect paraoxon at ppb level\nusing an automatable and cost-effective bioanalytical system.
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