Preparation Of Gold Nanoparticles-graphene Oxide Films And Their Application In Surface-enhanced Raman Scattering

In recent years, surface enhanced Raman scattering(SERS) was generally used in the widespread fields such as environment analysis, food safety and health as well as biomedicine et al. due to the easy operation, non-destructive measurement and high sensitivity of the SERS substrates. Recently, the SERS substrates fabricated by noble metal nanoparticles/graphene are very popular in Raman spectrum field. In this dissertation, we study on the design and preparation of SERS substrates with high sensitivity, good reproducibility and high stability by loading the gold nanoparticles onto graphene sheets. In this paper, the drop-coating method and dip-coating method were taken to synthesize gold nanoparticles/reduced graphene oxide(Au NPs/rGO) films. And the electrostatic self-assembly method was taken to fabricate the Au NPs/GO films. The formation processes of these two kinds of films were investigated in detail. And the effects of technique conditions on SERS performance were also demonstrated. The main contributions are described as follows:(1) The Au NPs/rGO nanoparticles were synthesized by non-toxic ascorbic acid reduction of chloroauric acid(HAuCl4) using microwave radiation method and GO was used as the supports. And then, the Au NPs/rGO nanocomposite films were obtained using the drop-coating method or dip-coating method. The results indicated that the reaction temperature, the reaction time and the mass ratio of reactant have major influence on the morphology and structure of the nanocomposites. According to our experiments, the optimal synthesis condition should be the temperature of 90 ℃, the reaction time of 20 min and the mass ratio between GO and HAuCl4 of 1:3. The Au NPs in nanocomposites have the size of 58.4 nm, with uniform morphology and high dispersion. The enhancement factor(EF) value of the Au NPs/rGO film fabricated by drop-coating method at band of 612 cm-1 reaches to 5.48×106 towards detection of Rhodamine 6G(R6G) molecules. The EF value of this composite film synthesized by dip-coating method is 2.23 times than the drop-coating method correspondingly. The results indicated that dip-coating method occupied the superiority in enhancing the Raman signal of R6 G molecules, compared with that of drop-coating method. Furthermore, the Au NPs/r GO film has obvious fluorescence quenching property to R6 G.(2) The positively charged Au NPs were firstly synthesized using the seed-growth method, which can be assembled with negatively charged GO sheets onto the quartz substrate. And then the Au NPs/GO films can be obtained by the electrostatic self-assembly method. The fabricated Au NPs/GO films have obviously superior SERS signal enhancement to R6 G molecules than that of pure Au NPs and GO film. The synergetic effect of electromagnetic of Au NPs and chemical effect of GO contributed most for SERS properties. The influence of assembly cycles on the morphology of Au NPs/GO films was also considered in this paper. Among the three different films, the film with twice cycle(F-2 film) has the best SERS performance compared with the film with once cycle and three-time cycles. The EF value of the F-2 film at band of 612 cm-1 reaches to 1.12×108, which is 20.4 times higher than the Au NPs/rGO film synthesized by drop-coating method. Simultaneously, the surface composition influence of the SERS property of the Au NPs/GO films was also investigated. The SERS performance of F-2 film with Au NPs on the surface is better than that of the F-2 film with GO on surface(F-2-GO film). Meanwhile, the F-2 film presented high sensitivity, satisfactory reproducibility and good stability. In detail, the detection limit lowered to 10-10 M and the relative standard deviation values of all Raman peaks of 11 random measurement points were less than 18%. In addition, such films also showed the good stability, the SERS Raman signals have no obviously weaken compared with the freshly fabricated sample.