ACTIVE Ag-NANOPARTICLES FOR HEAVY METAL IONS DETECTION.

Heavy metal pollution is a serious global environmental problem due to the adverse effects it is causing around the world. Therefore, a great deal of interest has developed versus sensors that allow to detect heavy metals using user-friendly and sensitive way. Colorimetric sensor-based on gold or silver nanoparticles (NPs) has increasingly been used thanks to their unique properties such as Localized Surface Plasmon Resonance (LSPR); this result in a strong absorption band in the visible region of the spectrum, depending on the size and shape of NPs and on dielectric constant of the medium. The most popular colorimetric sensor approach is based on metal nanoparticle aggregation [1]. In fact, a decrease in the interparticle distance, induced by the NPs assembly, change the plasmonic properties. To improve selectivity of this type of sensors, the NPs can be functionalized with ligands containing at least two functional groups, the tail that interact with the surface of particles, and the head that interact with the target molecules promoting the NPs aggregation [2]. In this study, the effect of functionalizing molecule (FM) density, on the variation of Surface Plasmon Absorption Band (SPAB) of AgNPs@FM induced by the addition of metal ions was investigated. The study demonstrated as to different FM concentration corresponded a particular AgNPs@FM behavior and therefore a definite shift of the SPAB. AgNPs@FM with different FM density were prepared and titrated by consecutively addition of metal ions (M); calibrations curves for each metal ions were obtained. It has been observed that, with a specific FM density, a second SPAB appeared at the wavelength related to each metal ions. Interestingly, different colors, related to different superlattice of AgNPs@FM@M were obtained allowing the identification of each metal ions. This preliminary investigation allows to understand how tuning FM density on the AgNPs allow to modulate the sensor response.