Comparison between silver and gold nanoparticles stabilized with negatively charged hydrophilic thiols: SR-XPS and SERS as probes for structural differences and similarities

The electronic and molecular structure, as well as the chemical nature of noble metal (silver, gold) nanoparticles (AgNPs, AuNPs) stabilized by the negatively charged hydrophilic organic thiol Sodium 3-mercapto-1-propanesulfonate (3-MPS) has been probed combining Synchrotron Radiation-induced X-ray Photoelectron Spectroscopy (SR-XPS) and Surface Enhanced Raman Spectroscopy (SERS). Complementary information about the electronic, chemical and molecular structure is obtained combining SERS and XPS data, allowing to evidence structural similarities and differences related to the noble metal choice. These results coherently suggest the effective 3-MPS chemical absorption onto the nanoparticle surface, which allows to obtain a stable and biocompatible system, suitable for ad hoc further functionalization as required for several applications in biotechnology. It was observed thattheNPsmolecularoverlayer ismadeupbycovalentbondsbetweenthiolsand metallicsurfaceatoms,without degradation of the molecule. The metals SR-XPS spectra analysis collected on the silver and gold nanoparticles points out a small surface to volume atomic percent ratio, as a consequence of the NPs size (≥5nm). Surfaceenhanced Raman Scattering (SERS) spectroscopy was employed for the investigation of the NP molecula