Sustainable olive pomace-derived AgNPs for sensitive colorimetric detection of cadmium in water

Cadmium (Cd2+) is a highly toxic contaminant that can be found in natural and drinking waters, where even trace level exposure can cause severe renal, skeletal, and immunological damage, highlighting the urgent need for rapid and sensitive detection methods. In this study, a novel colorimetric approach is described for detecting Cd2+ in aqueous environments, utilizing silver nanoparticles (AgNPs) synthesized through an eco-friendly method. The synthesis of AgNPs employs hydroalcoholic extracts derived from extra virgin olive oil production by-products (olive pomace), which function simultaneously as a reducing and stabilizing agent. The influence of pH, temperature, and concentration of the extract has been investigated and the AgNPs synthesis optimized. Comprehensive characterization of the AgNPs was performed using UV–Vis, Infrared, Dynamic Light Scattering spectroscopy and Scanning Electron Microscopy analysis, confirming their spherical shape, stability, and a distinct Localized Surface Plasmon Resonance (LSPR) band at 413 nm. The nanoparticles were used as colorimetric sensor for the determination of different metal cations, demonstrating high selectivity toward Cd2+. This was confirmed by the splitting of the LSPR band and the appearance of a new band at 530 nm, due to nanoparticle aggregation induced by Cd2+ ions, accompanied by a color change from yellow to brown. A calibration was performed in the linear range from 0.151 to 3.378 μM with a calculated limit of detection and quantification of 0.167 μM and 0.556 μM, respectively. The colorimetric assay was also successfully applied to natural water samples.