A disposable enzymatic electrochemical biosensor for amperometric organophosphorus pesticide determination based on a screen-printed carbon electrode (SPCE) platform was successfully developed. The working electrode consists of acetylcholine esterase (AChE) immobilized onto the surface of multi-walled carbon nanotube (MWCNT), chitosan (CS) and gold nanoparticle (AuNP)-modified SPCE. Ferricyanide was used as a redox mediator in solution. Two linear dynamic response ranges from 0.01 to 10 μg L-1 and from 10 to 100 μg L-1 were found for paraoxon-ethyl, with a detection limit of 0.03 μg L-1 (calculated as the amount of pesticide resulting in 10% of enzyme inhibition). High sensitivity was achieved due to a synergistic effect of AuNPs and MWCNTs deposited on the SPCE surface. Moreover, 83% of enzyme activity was retained after a dry storage period of 49 days (4 °C). Finally, the results of the electrochemical biosensor for paraoxon-ethyl-spiked spinach sample analysis showed a good agreement with those obtained from conventional HPLC.
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