The Preparation And Surface-Enhanced Raman Spectroscopy Effect Of Gold And Silver Nanoparticles

Coin metal (Au and Ag) nanoparticles (NPs) have been the most commonly used surface-enhanced Raman spectroscopy (SERS) substrates because of their special optical and electrical properties. The controllable fabrication of Au and Ag NPs and their study on optical properties have been very important for fundamental interests and practical applications. Their SERS activities are very sensitive to their shape, morphology and composition. Particularly, it could improve the SERS activity by fabricating the NPs with special morphology or core-shell structure. It is meaningful for the communities of nanomaterials, analytical chemistry, molecular biology and single-molecule spectroscopy.In this thesis, three different Au and Ag NPs (Au nanothorns, Ag nanostars, Au nanothorns@Ag NPs) had been prepared, and their SERS activities had been detaily studied. The meaningful results were obtained as following:1. We selected a type of thorn-shaped Au NPs with controllable morphology to investigate their SERS activity, and specially studied the effect of surface property (surface morphology and the nature of the metal-ligand interaction between probe molecules and the NPs). In our experiments, we had synthesized five different morphologies of Au NPs. They were characterized by ultraviolet-visible (UV-vis) absorbance spectra and transmission electron microscopy (TEM). Their SERS activities had been investigated by using Crystal violet (CV) and 4-mercaptobenzoic acid (p-MBA) as probe molecules. Differences in SERS enhancement were observed for Au NPs with different morphology. Au NPs with long thorns (Au LTs) exhibited the highest SERS activity using CV as probe molecules. The estimated EFs were 1.9×105 and 1.9×106 for perpendicular and parallel orientations, respectively. However, Au NPs with short thorns (Au STs) showed the highest SERS activity using p-MBA as Raman probes, and the estimated EF was 8.1×104. The results demonstrated that this type of Au nanothorns were SERS-active substrates, exhibiting much higher SERS activity than that of spherical Au NPs. Also, the surface property of the thorn-shaped Au NPs had great influences on their SERS activity.2. A novel and simple method had been developed for the synthesis of Ag nanostars. Ag nanostars were prepared by using ascorbic acid as the reducing agent to directly reduce AgNO3 solution in the absence of polymers and surfactants. The whole process was carried out at room temperature. The as-prepared Ag NPs were characterized by UV-vis absorbance spectra and TEM. Their SERS activity had been studied by using Rhodamine 6G (R6G) and p-MBA as probe molecules. The results indicated that Au nanostars were highly SERS-active substrates, showing much higher SERS activity than that of spherical Ag NPs.3. We used above Au nanothorns as the core to synthesize bimetallic Au nanothorns @Ag NPs with core-shell structure by seed-mediated growth technique. The as-prepared composite NPs were characterized by UV-vis absorbance spectra and TEM. Their SERS activity had been investigated by using R6G as Raman probes. The results indicated that Au nanothorns@Ag NPs were highly SERS-active substrates, and exhibited much higher SERS activity than that of Au nanothorns, spherical Ag NPs and Au@Ag NPs. It was also found that the SERS activity of Au nanothorns@Ag NPs was vety sensitive to the surface morphology of Au nanothorns core. When Au LTs were used as the core, Au nanothorns @Ag NPs showed the highest SERS activity.