Preparation And Applying On Surface Enhanced Raman Spectroscopy(SERS) Effect Of Gold And Silver Nano-materials

Nowadays, the research on surface enhanced Raman scattering has become a hot spot, due to its unique characteristics, such as the sample to be texted without complicated preparing process and the “print spectrum” with comprehensive information. And except the studies of enhance theories, the research contents including studies of enhance substrate as well, and these studies have progress rapidly. The enhance substrates usually use mental nanomaterial. To some degree, the enhance effect of the substrate depend on the chemical character and surface profile of the mental nanomaterial. Recently, though studies of mental nanoparticles surface enhanced Raman scattering technology have made some progress, simplifying fabrication method, improving the enhance effect of nanoparticles and application on detecting still need to be further explored. In the paper, the preparation and applying on surface enhanced Raman spectroscopy effect of gold and silver nanoparticles were studied, the main contents are:The effect of electromagnetic enhancement in SERS signal strength problem has been discussed. Based on the finite element method Comsol multiphysics simulation software, the SERS effects of sphere gold nanoparticles were simulated. By modelling single sphere and dual spheres gold nanoparticles with different diameters, simulate electric field distribution, and then calculate the SERS Enhancement Factor(EF), the results are as follows: when the incident light wavelength is 632.8nm, the diameter of single sphere gold nanoparticle is about 125 nm, the maximum of SERS EF is 1.46×102. But when the distance between dual sphere gold nanoparticles with the diameter of about 115 nm is 1nm, the maximum of SERS EF is 4.66×107, up to seven orders of magnitude. By comparison, we can see that SERS EF of bi-spherical gold nanoparticle is much larger than a single sphere of gold nanoparticle. Therefore, the dual sphere gold nanoparticles are more suitable for SERS substrates than a single sphere gold nanoparticle.Preparation of different diameters gold nanoparticles was investigated, in the process of preparing the gold nanoparticles, tri-sodium citrate was used as a reductant, reducing the solution of HAu Cl4 and make Au3+ to be Au0 monomer. The experiment adopted the method of heating the reactants to be boiling. And by controlling the reaction time and dose of reductant, different diameters of the gold nanoparticles could be obtained. Then detect the absorb spectrum by spectrophotometer. The result of the experiment shows that tri-sodium citrate reduces Au3+ in the solution of HAu Cl4 to be Au0 monomer, and form gold nanoparticles in reacting solution. Eventually, gold colloid with different color can be got by controlling the time of reaction and dose of reductants. And these gold colloids have different absorption peaks. According to the relationship between absorption peak and diameter of gold nanoparticle, the value of the diameter of the nanoparticle can be got, therefore different diameters gold particles could be made.Silver nanostructure martirals have been prepared by an easy replacement reaction between zinc and silver nitrate solution. And photos were taken by scanning electron microscope. The relationship between the replace reaction time and length of the the silver nanostructures was found. The silver nanoparticles were put on the silver chips. And by using the Rhodamine 6G as the molecule explorer, a SERS spectra has been obtained with raman spectrograph, then comparing the enhance effacts with and without the surfactants Polyvinylpyrrolidone(PVP). The expriment result shows that Silver nanostructures is dendritic, and the longer time the replacement reaction takes, the longer length the silver dendritic nanosubstractes becomes. By using dendritic silver nanosubstrates on the silicon chip, a good SERS spectra of Rhodamine 6G has been obtained, and it get the best SERS spectra when using the silver dendritic nanosubstractes whose preparing time is 40 s, and then the analytical enhancement factor is about 103. And when the silicon ship used with surfactants PVP, keeping the other coditions the same as before, the SERS spectra becomes better, and the enhancement factor turn to be about 104.Finally, nanosubstrate silver dendritic prepared by replacement reaction are used in detecting melamine added in pure water and milk powder. And by adding acetonitrile solution(50%) to milk powder contain melamine and shaking the mixture on a vortex mixer, the melamine are extracted from the milk powder into the acetonitrile solution. This liquid contain melamine is measured by a Raman spectrometer when the silver nanoparticles on sillicon chips are used as SERS-active substrates. An apparent enhancement effect can be seen by the spectra. What’s more, silver nanoparticles made out by oxidation-reduction reaction are also used in detecting melamine, and by changing the sillicon chips substrates to normal slides substrates, an apparent enhancement effect is still found in the SERS spectra of melamine. This behavior can cancel complex cleaning process of cillicon chips be cenceled when measuring. And the detection limit of the melamin solution is 10-5mol/L.