The neurotransmitter acetylcholine (ACh) is hydrolyzed by acetylcholinesterase (AChE) into acetic acid and choline to terminate synaptic transmission (1). Organophosphorus (OPs) found in pesticides induce toxicity in organisms by irreversibly binding to AChE, leading to the phosphorylation of the serine residue at the active site. ACh cannot undergo hydrolysis by the phosphorylated enzyme, resulting in excessive stimulation of nerves and muscles, akin to a nerve agent (2). Our objective is to develop a rapid detection tool for determining the levels of pesticide residues in dairy products. In this study, we measured the release of hydrogen ions (H⁺) resulting from the hydrolysis of ACh by AChE, serving as an indirect method to evaluate the inhibitory effect of OPs on AChE. To detect the signals of H⁺ released during ACh decomposition, we used ITO-coated nanostructures modified with 3-aminopropyl trimethoxysilane (APTMS) as a sensing substrate integrated into the extended gate of a field-effect transistor (EGFET) biosensor. The amino group at the end of APTMS can bond with H⁺. By monitoring the changes in electrical signal from the EGFET biosensor, it is possible to know the concentration of H⁺ in the solution. The output characteristics (I_d-V_d) of the APTMS-modified ITO-VASiNW EGFET were measured using ACh solutions at different concentrations. A correlation was observed between I_d and ACh concentration within the tested range, exhibiting a sensitivity of 0.016 mA^1/2 / mM and an R² value of 0.9. A lower concentration of H⁺ indicates a more pronounced inhibitory effect on AChE by OPs and suggests higher levels of pesticide residues.

References

(1) Colović, M. B., Krstić, D. Z., Lazarević-Pašti, T. D., Bondžić, A. M., & Vasić, V. M. (2013). Acetylcholinesterase inhibitors: pharmacology and toxicology. Curr Neuropharmacol,