Fabrication Of Reproducible Surface Enhanced Raman Scattering Substrate And Its Application

Surface enhanced Raman scattering (SERS) can extremely enhance the Raman signal of specific species adsorbed on the surface of nanostructures. It makes surface enhanced Raman spectroscopy (SERS) be a very sensitive spectroscopic technique for the detection of surface species, especially provides amount of qualitative information of molecules determination because of its high sensitivity, and thus widely used in many fields like surface chemistry, electrochemistry, analytical chemistry and biological detection. However, SERS shows very poor potential application in quantitative analysis due to poor reproducibility of its enhancement effect, relatively difficult repeatable detection abilities and the destitute lateral relative property of its substrates. Therefore, if the SERS substrates can be repeatable used in a level of quantitative detection, it will expand the SERS application and provide new insights. The main purpose of this thesis is to fabricate SERS substrates with improved uniformity and reproducibility and to study the relationship between the SERS intensities and the concentration of species adsorbed on the substrates in the condition of maintaining the SERS activity. The main achievements of this thesis are listed as follows:(1) Gold nanoparticles have been homogeneously coated with silica using the silane coupling agent (3-aminopropyl)-trimethoxysilane to functionalize the gold surface and sodium silicate solution as the precursor of silica. The shell thickness could be well controlled by changing the amount of sodium silicate, reaction temperature and time. By investigating the relationship between the intensity of SERS signals and the thickness of silica shell, we claim that the gold core doesn't work on enhancement effect to the species adsorbed on the surface of core-shell nanoparticles when the shell thickness is 7 nm.(2) The Au@SiO2 core-shell nanoparticles are self-assembled onto an poly(4-vinylpyridine) modified indium/tin oxide glass in order to get a homogeneous SERS substrate. This substrate has a better reproducibility than the naked gold substrate using silane coupling agent. We use a relative mild method for removing molecules from substrate. This process is consisting of washing the substrate with NaBH4 solution for about 3 min, then the SERS signal can obtained again.(3) In order to get a stable and reproducible SERS substrate used in on-line detection, monolayer gold nanoparticles are self-assembled onto an innerface of a capillary, followed by coating a shell of silica. The research of reproducible SERS measurements were performed by using 4, 4'-bipyridine, 1, 4-benzenedithiol and 4-mercaptobenzoic acid as probe molecules. Within a low concentration, the quasi-linear relationship between the SERS intensities and the logarithm of concentration was obtained. The detection limit was about 10-5 mol/L, and the results revealed that the Au@SiO2 nanoparticles assembled on the innerface of a capillary could be developed as a reproducible substrate for the on-line quantitative analysis.