•The effect of APFO and PFOA on AChE activity and inhibition had been investigated.•MALDI-FTICRMS was used to detect the activity of AChE.•AChE inhibitions from irreversible inhibitor were increased by adding APFO and PFOA.•APFO and PFOA had no obvious effect on AChE inhibitions from reversible inhibitor.Ammonium perfluorooctanoate (APFO) is a commercially important compound, but its harm to people's health has raised widespread concern. In the past, the investigations into APFO and its degradation product (perfluorooctanoic acid, PFOA) were all about their effect on indicator compounds in animals and enzyme activities. Here, we provided a new suggestion to investigate the influence of APFO and PFOA. Acetylcholinesterase (AChE) was chosen as research subject to reflect the effect of external perfluorochemicals. We applied matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (MALDI-FTICRMS) to detect the activity of AChE rapidly and accurately. On this basis, not only AChE activity but also AChE inhibition was studied carefully. The presence of APFO and PFOA showed obvious increase of AChE activity. Moreover, addition of both APFO and PFOA had enhanced AChE inhibition from organophosphorous (OP) pesticide (irreversible inhibitor). Otherwise, the participation of APFO and PFOA had not increased AChE inhibitions from reversible inhibitor galantamine. These results might provide new insights into the effect of APFO and encourage the deep understanding about effect of APFO on human being.

A simple and practical approach to improve the sensitivity of acetylcholinesterase (AChE)-inhibited method has been developed for monitoring organophosphorous (OP) pesticide residues. In this work, matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS) was used to detect AChE activity. Due to its good salt-tolerance and low sample consumption, MALDI-FTMS facilitates rapid and high-throughput screening of OP pesticides. Here we describe a new method to obtain low detection limits via employing external reagents. Among candidate compounds, n-octylphosphonic acid (n-Octyl-PA) displays assistant effect to enhance AChE inhibition by OP pesticides. In presence of n-Octyl-PA, the percentages of AChE inhibition still kept correlation with OP pesticide concentrations. The detection limits were improved significantly even by 102–103 folds in comparison with conventional enzyme-inhibited methods. Different detection limits of OP pesticides with different toxicities were as low as 0.005 μg L−1 for high toxic pesticides and 0.05 μg L−1 for low toxic pesticides. Besides, the reliability of results from this method to analyze cowpea samples had been demonstrated by liquid-chromatography tandem mass spectrometry (LC–MS/MS). The application of this commercial available assistant agent shows great promise to detect OP compounds in complicated biological matrix and broadens the mind for high sensitivity detection of OP pesticide residues in agricultural products.Graphical abstractIn the presence of n-octylphosphonic acid, the percentage of AChE inhibition caused by acephate pesticide was increased significantly. The enzyme inhibition still kept correlation with acephate concentrations. Monitoring of enzyme reaction and screening enzyme inhibitor in cowpea samples were based on MALDI-FTMS.Highlights► n-Octylphosphonic acid enhanced enzyme inhibition by organophosphorous pesticide. ► The detection limits were much lower than those of other enzymatic methods. ► This approach was applied in cowpea samples and confirmed by standard method.