| Because of nanoparticle having unique optic and electric property, ideal enhanced effect was observed on definite-size Au or Ag nanoparticles, and its enhancement factor can reach to 1014 on some"hot spot"between nanoparticles, which attracted extensive attention of scientists. DNA as biomacromolecules can be utilized as templates to build novel hybrid nanostructures. DNA has been exploited as a template for the fabrication of metallic nano-materials. It was found that the DNA acted as templates and reducing agent in formation of the novel nanostructure,so DNA was used in this article as an soft template for fabricating SERS substrate. Utilizing Tungstosilicate acid ion to synthesize nanoparticles was another an important method. Tungstosilicate acid could be as photocatalyst, stabilizer, oxidation agent, reducing agent and template. Basing on Tungstosilicate acid hard template, shape and size controlled synthesis of SERS sensitive substrate. Using these substrates, Ultrasensitive SERS Detection of TNT can be realized. The main results are summarized as follows1 We reported a very simple and novel one-step in-situ method to synthesize silver-core-gold-shell or silver-gold alloy nanoparticles by sunlight-reducing in AgNO3 solution and NaAuCl4 solution in the presence of DNA. It was found that the DNA acted as template and reducing agent in formation of the novel nanostructure. The Ag-DNA could be formed from reduction of cationic silver absorbed on DNA template by sunlight. The silver-core-gold-shell or silver-gold alloy nanostructures were prepared by seeding with Ag-DNA in the absence of any surfactants, which could be used as active surface enhanced Raman scattering (SERS) substrates. 2,4,6-trinitrotoluene (TNT) was studied on these substrates with very low concentration (10-12 M), and great enhancement factors (3.1×1011-1.5×1012). It was found that the enhancement ability was affected by the structures of the gold and silver nanoparticles on the DNA strands. The results showed that these SERS substrates could achieve current the lowest detection limits of TNT.2 Trace-detection of TNT is reported in this work basing on p-aminothiophenol functionalized Ag nanoparticles covered on Silver molybdate nanowires by using surface-enhanced Raman scattering (SERS).π-donor-acceptor interactions betweenπ- acceptor TNT andπ-donor p,p′-dimercaptoazobenzene (DMAB)-cross-linked Ag nanoparticles linked to the Silver molybdate nanowires, the optimal imprint molecule contours, and DMAB forming imprint molecule sites at SERS hot spots where the analyte can be allocated, these lead to a giant intensification of the Raman emission of the TNT molecule. This article demonstrates that TNT concentrations as low as 10-12 M can be accurately detected using the described SERS assay. Most impressively, acting as new-style SERS substrate, Ag-Silver molybdate nanowires complex can yield new Ag nanoparticles during detection process which made the Raman signals very stabilization. A detailed mechanism for SERS intensity change has been discussed. Our experiments show that TNT can be detected quickly and accurately with high trace-concentration. These results reported here not only can find many applications in SERS techniques but also can form the new concept of a molecularly imprinting strategy.
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