The Preparation Of Au@SiO₂ And Its Application In SERS

Surface enhanced Raman Scattering?SERS? technique has been widely applied to food safety, electrochemistry, biomedicine and other fields due to its high detection sensitivity. It was known as SERS. This technology can be compared with single molecule fluorescence. However, a fatal drawback is that only a few metals?mainly Au, Ag and Cu? and alkalinous metals?for example Na and K? have a large SERS effect. Moreover, the alkali metals are hardly exist as elemental forms in nature environment. Therefore, Au, Ag, and Cu are mainly used to prepare SERS substrates. Their Raman activity is: Ag > Au > Cu. Unfortunately, Ag nanoparticles?NPs? are easily oxidized, correspondingly, their Raman activity is greatly reduced in the nature environment. This disadvantageous factor hinders the practical application of Ag NPs. In addition, the morphology of the Ag NPs is so hard to control that their universality is poor. In view of the above, it is important to develop a simple, rapid, convenient and high sensitivity, high reproducibility, stability SERS substrates.In this paper, we have prepared a series of Au@SiO₂ NPs with different shell thickness and different core thickness using the Stober method and the method reported by Professor Jianfeng Li in Xiamen University. Then the Au@SiO₂ NP monolayer film was transferred to a solid support?Au substrate and Si substrate? for further experiment. Ultimately, Au@SiO₂ NPs were studied systematically and comprehensively to analyze the relationship between their nanostructures and SERS activity. In addition, we studied the adsorption behavior of dye molecules on Au@SiO₂ NPs surface by signal analysis and theoretical calculation, and try to apply them to other areas. The main research contents and conclusions are as follows:1. The average diameter 15 nm, 25 nm, and 50 nm of Au NPs were prepared by the sodium citrate reduction method under the 125?. Then Uv-vis spectroscopy, SEM, and TEM were used to characterize the morphology and size of Au NPs.2. A series of Au@SiO₂ NPs with different shell thickness and different core thickness using the Stober method and the method reported by Professor Jianfeng Li in Xiamen University. Au@SiO₂ nanoparticles?NPs? with 2-3 nm shell thickness, and ca. 15 nm, 25 nm, 50 nm core sizes were prepared, respectively. Meanwhile, Au@SiO₂ NPs with 25 nm core size, and ca. 3 nm, 15 nm, 35 nm, 50 nm shell thickness were prepared.3. The different core size and different shell thickness of Au@SiO₂ monolayer film were prepared, and then transferred on a hydrophilic solid surface?Si and Au substrate?. Using Rhodamine 6G?R6G? as probe molecules to study the EM coupling effect relationship between the particles size and gap. Meanwhile, the sensitivity, reproducibility, and stability were systematically studied, and then using it to study the ADSORPTION behavior of the molecules on the Au@SiO₂ NPs surface, and introduction of Au@SiO₂ NPs to prove double diffusion model of holographic.4. The FDTD method was used to simulate the EM field strength in the vicinity of Au@SiO₂ NPs dimer under the air and different substrates, then analysis and verify the experiment data.