A SERS investigation of antimicrobial adsorption on silver nanoparticles as mediated by surface modifiers

In this work, the adsorptions of the antimicrobial drugs aztreonam, tinidazole and metronidazole on silver nanoparticle surfaces were investigated using surface-enhanced Raman scattering (SERS) spectroscopy. The chemical properties of silver surface were modified by using mercaptoethanol, polyvinyl alcohol or chloride ions for changing the adsorption mechanisms, which led to distinct SERS spectral patterns. These were analyzed regarding the proximity of molecular moiety from the analyte to the silver surface. The adsorption processes were monitored by the localized surface plasmon resonance bands, which were recorded through ultraviolet-visible spectroscopy. Theoretical models were obtained from density functional theory and used for supporting the vibrational assignments. The analyses of the SERS spectral patterns allow inferring aztreonam adsorbed through carboxylate moiety while tinidazole and metronidazole adsorbed via nitro group. The surface modifiers led to changes of the adsorption geometries of the molecules on the silver surfaces, which were rationalized based on differences in the relative intensities of the bands assigned to the out-of-plane modes. Copyright © 2017 John Wiley & Sons, Ltd.