Lin_2020_Food.Chem_345_128809

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.