Preparation and characterisation of gold nanoparticle assemblies on silanised glass plates

Gold nanoparticles were prepared by the chemical reduction of AuCl4− and attached to aminopropyltrimethoxysilane-treated glass plates. The assemblies of gold nanoparticles on silanised glass were characterised by UV spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and surface-enhanced Raman scattering (SERS). The gold nanoparticles had a diameter in the range 40±10 nm as estimated by AFM. Gold was found to be in the metallic state as judged from XPS measurements of the Au 4f7/2 core electron binding energy. AFM showed that the gold nanoparticles experience a self-organisation on the silanised surface in such a way that the final assemblies have a certain degree of roughness and compactness. These characteristics are intimately related to the SERS effect as determined using the molecular probe bi-ethylene-pyridine at very low concentration. A huge enhancement of the Raman signals was observed and assigned to a coupling between gold particles. However, this SERS effect critically depends on the surface treatment of the substrate by the silane coupling agent, a procedure that is necessary for the attachment of the gold nanoparticles.