| Metal nanostructures exhibit remarkable optical properties due to their surface plasmon resonance. Based on the SPR property, surface enhanced spectroscopy (SES) points to the very promising future in the nanomaterial domain, of which surface enhanced Raman spectroscopy (SERS) and surface enhanced fluorescence spectroscopy (SEFS) are widely investigated. With the development of nanotechnology, SERS research developed rapidly. However, theoretical studies of SERS phenomenon, the reproducibility of SERS spectra, the expansion of substrate materials as well as the generality of surface morphology are the pivotal aspects all the SERS researchers devote to. For SEFS, utill recently, experimental and theoretical research has also made a major breakthrough. Metallic nanoparticles have been shown to enhance the fluorescence emission, decrease the molecular excited-state lifetimes of vicinal fluorophores, enhance the quantum yield, and stabilize adjacent fluorophores against photobleaching. These advantages make SEFS detection in biological analysis, and many other areas of the prospects for broader application. At the present time, most of the SEFS researches focus on two aspects: 1) enhancement in the vincity of LSPR tunable nanoshells and nanorods ranging into NIR region in solution. 2) enhancement on the silver-island films formed either by chemical deposition from solution or by evaporation of silver under high vacuum. Few researches utilizing self-assemble anisotropic metallic nanocrystal films were reported. As is well-known, SERS and SEFS are both intensively dependent on the metallic nanostructure. Therefore, the surface enhanced spectroscopy can be controllably researched by optimizing the nanoparticle topology and assembly dimensions, which will greatly promote the development of the SES theory and applications. Based on the SES development, our study is outlined as follows: 1. The light-driven growth method has been proven to be one of the most successful approaches to produce size- and shape controlled metallic nanoparticles. However, the origin of anisotropic growth in the photoinduced growth process is not related to plasmon excitation but rather to intrinsic aspects of the seeds, such as structural defects or the capping reagent. Successfully utilizing tartrate and citrate as structural-directing reagents at the appropriate stages of reaction, we have prepared, in large scale, regularly tetrahedral silver nanocrystals developed from silver spherical seeds through a light-driven method. The growth process is monitored by ultraviolet-visible spectroscopy and transmission electron microscopy. A preliminary growth mechanism of TSNCs is proposed. For the Td symmetry, TSNCs display a striking beauty and show their intriguing optical properties for the research fields such as surface enhanced spectroscopy, as well as plasmonic materials.2. The sharp vertexes of TSNCs can generate strong localized electromagnetic field for SERS studies. The nanocrystals were assembled through electrostatic interaction to develop large-scale particle surfaces with sharp vertexes. Compared to the truncated tetrahedral Ag nanoparticle arrays formed by nanosphere lithography (NSL), researches of single-crystal nanoparticles assembly film will enable us to obtain the most essential information of nanoparticles. Benzenethiol and 4-mercaptopyridine were used as the probes to evaluate their SERS enhancement, and enhancement factors of up to 106 were reached. SERS substrates with high reproducibility were formed through layer-by-layer electrostatic assembly of TSNCs. Finally, the SERS enhancement ability of self-assembled quasispherical nanoparticles, triangular nanoplates and tetrahedral nanocrystals films was studied. When the LSPR bands of these nanoparticles were not exactly matched with the excitation laser line, the SERS activity of quasispherical silver nanoparticles was significantly stronger than the triangle and tetrahedron due to the exposed active crystal faces and"hot spots"between the adjacent nanoparticles. Under the same experimental condition, the SERS activity of TSNCs is higher than the triangular nanoplates.3. The application of self-assembled TSNCs films were extended to SEFS. Polyelectrolyte multilayers were used as the effective spacing layers between the TSNCs films and fluorophore. Under the optimized spacing bilayers, using Atto 610 as a probe molecule, we investigated the metal enhanced fluorescence of TSNCs: enhanced fluorescence and fluorescence quenching / fluorescence and enhanced fluorescence. Compared with Atto 610 on a glass slide, the fluorescence intensity was enhanced by about 3-fold by the TSNCs. Tetrahedral silver nanocrystals must then be invaluable as a core material of molecular sensors operating via both SERS and SEFS.4. The Ag substrate was found to meet the essential criteria of a truly useful SERS substrate for application relevant to surface chemical analysis: strongly enhancing, reproducible, easy to fabricate and store. We reported a uniform silver surface prepared by silver nucleation in the PEM and silver-enlarged growth in Li Silver. This method has several advantages. First, the uniform size of the Ag nuclei in the PEM optimized the dispersion of Ag aggregates in the following Ag growth step. Secondly, the application of Li Silver has proved to be an effective and simple approach for controlling the surface morphology of the silver-containing film. Rhodamine 6G and 4-mercaptopyridine were used as Raman probes to evaluate the enhancement ability of the new Ag substrate. It is found that the novel silver surface is an effective SERS-active substrate that can not only provide strong enhancement factors and greater reproducibility, but is also facile and relatively inexpensive to fabricate and store.
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