Double-enzymes-mediated fluorescent assay for sensitive determination of organophosphorus pesticides based on the quenching of upconversion nanoparticles by Fe3+

Herein, a new double-enzymes-modulated fluorescent assay based on the quenching of upconversion nanoparticles (UCNPs) by Fe 3+ was constructed for sensitive determination of OPs. OPs can inhibit the activity of acetylcholinesterase to reduce the production of choline and further lead to the lack of H 2 O 2 in the presence of choline oxidase. Therefore, Fe 2+ cannot be converted into Fe 3+ , resulting in “turn-on” fluorescence of UCNPs. Under optimal conditions, an excellent linear correlation between the inhibition efficiency and the logarithm of the chlorpyrifos concentration was achieved with a detection limit (LOD) of 6.7 ng/mL in the range of 20–2000 ng/mL. The recovery for chlorpyrifos in apples and cucumbers was 89.5–97.1%. The results were consistent with those obtained by GC–MS. Overall, the integration of UCNPs into the double-enzymes-mediated Fe 3+ /Fe 2+ conversion endows this method with desirable rapidity, sensitivity, selectivity, stability, operational simplicity, and strong anti-interference capability, holding great potential in the application of food safety.