Investigating gold nanorod-mediated hydrolysis of acetylthiocholine: A way for electrochemical detection of organophosphate pesticides

Pesticides and their metabolites threaten the environment and human health even at low concentrations. Therefore, the development of sensors to track such substances is crucial. Nanoparticle-based sensors have been widely used recently as a possible substitute analytical tool to traditional pesticide detection techniques. Artificial enzymes, also known as enzyme mimics or nanozymes, are gaining attention due to their innate ability to overcome the limitations of natural enzymes and their efficacy to be sufficient for upcoming advancements in treatments and diagnostics. Nanozyme-based assays may enable organophosphate pesticide detection without relying on the natural cholinesterase enzymes while retaining similar or higher sensitivity at a lower cost. Therefore, the present work investigates the acetylthiocholine (ATCH) hydrolyzing ability of gold nanorods (GNRs) through colorimetric, computational, and electrochemical methods. The GNRs were observed to intrinsically exhibit ATCH hydrolyzing ability, like acetylcholine esterase (AChE). Further, the effect of different organophosphates (OPs) (malathion, methyl parathion, chlorpyrifos, parathion, and dichlorvos) on the ATCH hydrolyzing ability of nanostructures was studied using an electrochemical approach. Their activity was significantly quenched in the presence of malathion and methyl parathion as compared to other OPs. The increasing order of OP's inhibitory effect was malathion>methyl parathion>dichlorvos>chlorpyrifos>parathion. It was observed that inhibition was proportional to the increasing concentration of OPs, and the linear range of detection was 0.0005-200.0 µg mL-1, with a limit of detection (LOD) of 8.1 pg mL-1 and 30.2 pg mL-1 respectively, for malathion and methyl parathion. Validation of river water samples spiked with different concentrations of malathion shows good recovery in the range of 100–110 %. Keywords: Acetylthiocholine; Cyclic Voltammetry; Electrochemical; Nanozyme; Organophosphate; Gold nanorod