Oxidative desorption of thiocholine assembled on core–shell Fe3O4/AuNPs magnetic nanocomposites for highly sensitive determination of acetylcholinesterase activity: An exposure biomarker of organophosphates

Acetylcholinesterase (AChE) activity is a well established biomarker for biomonitoring of exposures to organophosphates (OPs) pesticides and chemical nerve agents. In this work, we described a novel electrochemical oxidative desorption-process of thiocholine, the product of enzymatic reaction, for rapid and highly sensitive determination of AChE activity in human serum. This principle is based on self-assembling of produced thiocholine onto core–shell Fe3O4/Au nanoparticles (Fe3O4/AuNPs) magnetic nanocomposites and its oxidation at electrode surface. Fe3O4 magnetic core is not only used for magnetic separation from sample solutions, but also carrying more AuNPs due to its large surface-to-volume ratio. The core–shell Fe3O4/AuNPs nanocomposites were characterized by UV–Vis spectroscopy, field-emission scanning electron microscopy (FE-SEM) and electrochemical measurements. A linear relationship was obtained between the AChE activity and its concentration from 0.05 to 5.0 mU mL−1 with a detection limit of 0.02 mU mL−1. The method showed good results for characterization of AChE spiked human serum and detection of OP exposures from 0.05 to 20 nM, with detection limit of 0.02 nM. This new oxidative desorption assay thus provides a sensitive and quantitative tool for biomonitoring of the exposure to OP pesticides and nerve agents.