Silver nanoparticles capped with 3-mercapto-1propanesulfonic acid sodium salt (AgNPs-3MPS), able to interact with Ni2+ or Co2+, have been prepared to detect these heavy metal ions in water. This system works as an optical sensor and it is based on the change of the intensity and shape of optical absorption peak due to the surface plasmon resonance (SPR) when the AgNPs-3MPS are in presence of metals ions in a water solution. We obtain a specific sensitivity to Ni2+ and Co2+ up to 500 ppb (part per billion). For a concentration of 1 ppm (part per million), the change in the optical absorption is strong enough to produce a colorimetric effect on the solution, easily visible with the naked eye. In addition to the UV-VIS characterizations, morphological and dimensional studies were carried out by transmission electron microscopy (TEM). Moreover, the systems were investigated by means of dynamic light scattering (DLS), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and high-resolution X-ray photoelectron spectroscopy (HR-XPS). On the basis of the results, the mechanism responsible for the AgNPs-3MPS interaction with Ni2+ and Co2+ (in the range of 0.5–2.0 ppm) looks like based on the coordination compounds formation.

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Hydrophilic gold and silver nanoparticles stabilized with 2-diethylaminoethanethiol hydrochloride (DEA) have been prepared and characterized. AuNPs-DEA and AgNPs-DEA with mean diameter below 10 nm have been characterized by means of dynamic light scattering and fieldemission scanning electron microscopy techniques. Nuclear magnetic resonance (NMR) studies allowed to assess translational mobility, aggregation equilibrium in function of pH variations and presence of chemisorbed and physisorbed thiol molecules; in particular ethyl groups on DEA ligands are free to rotate, suggesting a rather loose packing of the thiols on the nanoparticle surface. NMR results were compared with X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure, and X-ray absorption spectroscopy. The complementary information acquired allowed to obtain information on the interaction at the interface between the organic thiol ligand and metal nanoparticles (NPs) at atomic level as well as on the molecular structure. The influence of the thickness of the functionalizing layer on the stability of NPs has been studied and opened new insight on the local structure surrounding the NP

Gold nanoparticles with an average diameter of 10 nm, functionalized by the dye molecule rhodamine B isothiocyanate, have been synthesized. The resulting material has been extensively characterized both chemically, to investigate the bonding between the dye molecules and the nanoparticles, and physically, to understand the details of the aggregation induced by interaction between dye molecules on different nanoparticles. The plasmonic response of the system has been further characterized by measurement and theoretical simulation of the static UV-Vis extinction spectra of the aggregates produced following different synthesis procedures. The model parameters used in the simulation gave further useful information on the aggregation and its relationship to the plasmonic response. Finally, we investigated the time dependence of the plasmonic effects of the nanoparticles and fluorescence of the dye molecule using an ultrafast pump-probe optical method. By modulating the quantity of dye molecules on the surface of the nanoparticles it was possible to exert fine control over the plasmonic response of nanoparticles.

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