Preparation Of Reduced Symmetrical Metal Nanoparticles And Their Surface-enhanced Raman Scattering Activities

Metal nanostructures are of great interest due to their unique optical, electrical, mechanical, and chemical properties. These properties of a metallic nanostructure are mostly determined by its size, shape, structure and dielectric environment.In which, the surface plasmon resonance properties has have attracted much interest. Based on their surface plasmon resonance properties, metal nanoparticles have been widely applied in the fields of cancer therapeutics, nanoscale optical devices, chemical and biological sensors, surfaceenhanced fluorescence and surface-enhanced raman spectroscopies.Gold, silver nanocaps have been prepared with a general chemical strategy by depositing gold, silver films on top of self-assembly close-packed monolayer of SiO2 nanoparticles, Their surface morphologies, crystal structures, and optical properties have been characterized and investigatedusing TEM, SEM, AFM, XRD, UV-Vis and spectrophotometers.TEM results showed that the prepared SiO2 nanoparticles were uniform in size distribution and had a good monodispersity. SEM images revealed that the self-assembled SiO2 microspheres templets exhibited two dimensional close-packed monolayer arrays. High resolution SEM and AFM images indicated that the surfaces of the composite nanoparticles were not smooth, being characterized by numerous small silver grains and incompletely encapsulated. XRD results showed that the Ag films prepared on the top of SiO2 nanoparticles were found to be good crystalline. UV-Vis-NIR absorption spectra showed that the cap-shaped composite nanoparticles had a highly tunable SPR, and their SPR could be easily tuned from the ultraviolet to the visible or even the near-infrared region by changing the relative ratio of the core diameter to the cap thickness.The surface-enhanced raman scattering (SERS) activities of the SiO2/Au, SiO2/ Ag cap-shaped composite nanoparticles have been investigated using methylene blue (MB) as probe molecules, and their enhancement factors have been estimated to be as large as 10 billion. The results indicated that the cap-shaped noble metals nanoparticles prepared on the top of SiO2 nanoparticles were good SERS-active substrates, which recommended them as promising candidates for ultrasensitive chemical and biological detection.