Green synthesis of silver-chitosan nanocomposites for colorimetric detection of malathion in aqueous systems

This study presents a green hydrothermal synthesis of silver-chitosan nanoparticles (AgCs NPs) as a bio-based colorimetric platform for malathion (MLT) detection. Chitosan (Cs) served as both a reducing and stabilizing agent, enabling the formation of spherical AgNPs, as characterized by UV–Vis spectroscopy, ATR-FTIR, ¹H-NMR, XRD, and TEM. Among the investigated Cs/AgNO 3 ratios, AgCs-6 NPs exhibited the optimal balance between colloidal stability and sensing performance, with TEM particle size ranging from of 25.2 to 49.9 nm. Exposure to MLT produced concentration-dependent optical changes. Quantitative UV-Vis analysis at 280 nm provided the lowest instrumental limit of detection (LOD) of 0.319 ppm, while the A 280 /A 420 and logarithmic ratiometric approaches yielded LODs of 1.015 and 0.943 ppm, respectively. AgCs-6 NPs showed a preferential optical response toward MLT compared with DDVP, PMP, and CAB. Combined UV-Vis, TEM, ζ-potential and FTIR analyses suggest that the sensing response arises from MLT interactions at the Ag/Cs interface, where the Cs-rich surface contributes to MLT recognition and colloidal stabilization, while the Ag component provides the plasmonic response. These interfacial interactions alter the local optical environment and may promote limited interparticle association without causing extensive aggregation. These findings demonstrate the potential of AgCs NPs as a bio-based colorimetric sensing platform for MLT detection in aqueous systems.