SPECIFIC AND SELECTIVE SERS ACTIVE SITES GENERATION ON SILVER NANOPARTICLES BY CATIONIC AND ANIONIC ADATOMS

The here proposed specific adatom approach for surface-enhanced Raman scattering (SERS) highlights the fact that the Raman enhancement originates from the electronic coupling of the analyte with the metal surface, mediated by specific ions that form SERS active sites on the surface of the nanoparticles. The spectra of anionic and cationic analytes can be recorded specifically by generating specific SERS active sites, obtained by adsorbed ions (adions) such as Ca2+ and Cl-, respectively. Thus, the SERS spectrum of anionic and cationic species is turned on by the electronic coupling of the analyte with the metal surface at such SERS active sites. Moreover, the selective SERS turn on of anions, like citrate and Cl- from their mixture is determined by their competitive adsorption to the metal surface. Furthermore, a proportional dependence of the SERS intensity with the number of SERS active sites was observed. The sequential detection of the three analytes, citrate, chloride and Nile Blue in the same solution can't be explained by a model based on the aggregation of the nanoparticles. In the adatom approach, the aggregation of the nanoparticles is an unnecessary step that rather contributes to the low reproducibility of SERS spectra. We strongly believe that the proposed specific adatom approach will lead to a better understanding and control in SERS spectroscopy, thus improving the predictability of the method.