A sensitive fluorescent assay for the determination of parathion-methyl using AHNSA probe with MnO₂ nanosheets

In this paper, a novel fluorescence assay has been constructed for the determination of parathion-methyl (PM) by using 4-amino-3-hydroxy-1-naphthalenesulfonic acid (AHNSA) as probe. MnO₂ nanosheets (MnO₂ NS) could quench the fluorescence of AHNSA, while Mn²⁺, the reduction product of MnO₂ NS, has no influence on it, resulting in fluorescence recovery. This is because that MnO₂ NS have oxidized characteristic, and they can react with choline (TCh), which is the product of acetylthiocholine (ATCh) catalyzed by acetylcholinesterase (AChE). In the presence of OPs, the activity of AChE was inhibited, accompanied by the restraint of the redox reaction of MnO₂ NS, therefore the fluorescence of AHNSA was quenched. Under the optimized experimental conditions, a linear range of PM was determined to be 0.4-40 ng/mL (R² = 0.997) by the proposed method with the limit of detection for 0.18 ng/mL (S/N = 3). The assay was successfully applied to the determination of PM in lake water, which average recoveries were between 86.5% and 114.4%.