Probing the enhancement mechanisms of SERS with p-aminothiophenol molecules adsorbed on self-assembled gold colloidal nanoparticles

Gold colloidal nanoparticles were immobilized upon a glass substrate and their morphology and optical properties are analyzed with TEM and UV–Vis absorption spectroscopy. The substrate suitability for surface-enhanced Raman spectroscopy (SERS) in visible and near-infrared spectral region is demonstrated with four excitation lines using p-aminothiophenol. The SERS spectra of probing molecules exhibit a clear signature of electromagnetic and charge-transfer enhancement mechanisms, which critically depend on the laser lines. The large tunability of surface plasmon excitation combined with the advantage of highly chemical affinity to gold of probe molecules recommends this SERS-active system as a useful model for probing the mechanisms of Raman enhancement.