Construction of composite surface-enhanced Raman scattering(SERS) substrates by silver nanoparticle assembly

Metal-molecule-metal sandwich structures on quartz slides were constructed by the self-assembly of Ag nanoparticles with various shapes via p-aminothiophenol(PATP) molecules as linkers. These sandwich structures were characterized by extinction spectroscopy and surface-enhanced Raman scattering(SERS) spectroscopy using different excitation lasers. The results demonstrated that SERS intensities of PATP in sandwich structures were much stronger than those on silver nanoparticle monolayers. The calculated enhancement factors(EFs) of PATP on the composite SERS substrates showed that the large EFs appeared when the SPR peaks of SERS substrates well matched excitation lines. In these sandwich structures, PATP molecules tended to form a new surface species(p, p'-dimercaptoazobenzene, DMAB) under a laser-induced catalytic coupling reaction. In addition, the laser-induced catalytic coupling reaction was closely related to excitation wavelengths.