Facile and visual detection of acetylcholinesterase inhibitors by carbon quantum dots

Abstract

Sensitive and rapid detection of organophosphate toxicants is highly relevant and important in environmental protection and food safety. Owing to this, a carbon quantum dot (CQD)-based bio-platform was designed for dual detection (fluorometric and colorimetric) of reversible and irreversible inhibitors of enzyme acetylcholinesterase (AChE). The detection strategy is based on the fluorescence quenching and recovery of CQDs through Cu²⁺ ions, AChE and its substrate, acetylthiocholine iodide (ATChI). Initially, enhanced fluorescence of CQDs is effectively quenched by Cu²⁺ ions and later on recovered by catalytic hydrolysis of ATChI via the formation of Cu–S bonds by release of thiol compounds. In the presence of inhibitors, the fluorescence of CQDs remains quenched due to the blocked activity of the enzyme but in the presence of oximes the fluorescence is recovered depending upon the ability of the oxime reactivators to regenerate AChE. The fluorescence quenching and recovery is visible with color variations. The sensor facilitates good sensitivity for quick detection of both reversible (CPC, 0.62 ng mL⁻¹; Triton-X; 1.02 ng mL⁻¹) and irreversible (paraoxon, 0.21 ng mL⁻¹; chlorpyrifos, 0.46 ng mL⁻¹) inhibitors. However, strong inhibition of AChE is a major hurdle in practical implementation of biosensors; hence, the system is tested for reactivation of inactivated AChE by monopyridinium oximes and percentage reactivation was also calculated.