Rapid and simple nanosensor by combination of graphene quantum dots and enzymatic inhibition mechanisms

•Graphene quantum dots are proposed as fluorescent probes for fenoxycarb determination.•Acetylcholinesterase was chosen as biorecognition element in the procedure.•Quenching effect of reaction products on nanoparticle fluorescence allowed for detection of fenoxycarb inhibitor.•The fluorescence recovery was dependent on fenoxycarb concentration.•Analysis of river water was successfully performed through the developed sensing method.

In this paper, we report a simple, rapid and reproducible sensing approach for determination of fenoxycarb pesticide in river water based on the combined use of nitrogen-doped graphene quantum dots (N-GQDs) and acetylcholinesterase (AChE) enzyme as biorecognition element. Nanoparticles were used as fluorescent probes, while AChE was employed for inhibitor screening. The enzyme-generated products quenched the native fluorescence of N-GQDs. When fenoxycarb was introduced into the assay solution, the activity of AChE to convert substrate into products resulted to be reduced and consequently, N-GQD fluorescence was recovered gradually in an inhibitor concentration-dependent manner. Preliminary studies showed that nanoparticles were not directly sensitive to fenoxycarb, however, the inclusion of an enzymatic system in solution allowed for successful determination of pesticide in aqueous samples. Under optimized conditions, fenoxycarb concentrations ranging from 6 to 70 μM exhibited an excellent linear relationship with the inhibition efficiency percentage (R2 = 0.9941). The proposed biosensor has a limit of detection (LOD) of 3.15 μM, and excellent reproducibility values (RSD <3%) in river water analysis. Additionally, this analytical strategy is rapid and simple, and it provides a promising alternative for assaying AChE activity and screening of its inhibitors.

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