Encapsulating acetylcholinesterase (AChE) into metal-organic frameworks for selective and sensitive colorimetric detection of carbaryl residue in water samples

This study presents the development of an AChE@ZIF-8 composite biosensor using a gold nanoparticle (AuNPs) probe as a naked-eye signal readout platform for the sensitive detection of carbamate pesticides. As a biomarker for carbaryl monitoring, we present the encapsulation of acetylcholinesterase within zeolitic imidazolate frameworks-8 (AChE@ZIF-8) to enhance its stability without losing its intended functions. In this research, synthesis work of AChE@ZIF-8 was carried out using a biomineralization approach and characterized by Powder X-ray Diffraction (PXRD), Fourier Transform Infrared (FTIR), Thermogravimetric analysis (TGA), and Brunauer-Emmett-Teller (BET). Computational modelling using Gaussian 16 was employed to provide qualitative electronic insight into the system. The encapsulation efficiency (EE%) of AChE within the ZIF-8 matrix was found to be 97.60%, which indicates highly effective enzyme loading and confirms the suitability of ZIF-8 as a robust carrier for enzyme immobilization. Acetylcholine (ACh) is catalysed by acetylcholinesterase to produce choline, which results in gold nanoparticles aggregating and a corresponding colour change. Under optimal conditions (temperature: 37 °C, buffer pH: 7.6, incubation time: 20 min, and ACh concentration: 4 mmol/L), the colour change can be employed for the detection of carbamate pesticides at low concentrations, with rapid sensitivity for carbaryl detection at a detection limit of 4.95 nM, and shows consistent performance in the analysis of spiked real water samples, achieving recoveries of 92.2-103.3%. AChE@ZIF-8 exhibits strong stability during biological storage, making it feasible for on-site carbaryl detection and showing great potential for wider applications in water pollutant monitoring.