| Due to its unique nanostructure and extraordinary properties such as excellent optical, electrical, mechanical property, great specific surface area and high chemical stability et, graphene (GE) and GE based composite materials have shown great promising applications in electronics, optics, sensors, catalyst, supercapacitor, new energy battery etc. In recent years, the surface-enhanced Raman scattering (SERS) activity became an important research direction of GE and GE based materials and has shown promising applications in diverse areas, including chemistry, forensic analysis, food safety, threat detection and medical diagnostics. In this dissertation, in order to obtain the substrate with high SERS activity, the vacuum-filtration method and dip-coating technique were used to prepare the (ultra thin) GE films and the (ultra thin) silver-nanoparicles/graphene (Ag NPs/GE) films. And the formation mechanism and technological influencing factors of the films were investigated. Simultaneously, the relationship between the microstructure and the light transmittance, electrical conductivity, especially the SERS activity was discussed. The optimum conditions for preparing the Ag NPs/GE substrate with high SERS activity have been put forward and the results make a great contribution to the pratical Raman detection.The graphene oxide (GO) was synthesized by the Hummers method in this experiment to prepared the GE films via vacuum-filtration method and dip-coating technique. It is well known that the oxygen-containing groups of GO carry negative charges, which made the positively charged Ag NPs combine with the GO faultlessly by electrostatic self-assembly process to obtain the Ag NPs/GE (ultra thin) films. And the influence of the reduction process on the microstructure and properties of films were investigated in detail. The results showed that the free-standing GE films with controllable size and high electrical conductivity could be obtained by vacuum-filtration method followed by two-step reduction process, but the SERS activity was not obvious. To the Ag NPs/GE films, the Ag NPs distributed uniformly among the GE papers and on the surface. The Ag NPs/GE films exhibited excellent SERS property toward rhodamine6G(R6G), crystal violet(CV), and Escherichia coli (E. coli). The high SERS-activity of Ag NPs makes a significant contribution to the high sensitivity of the Ag NPs/GE film. The enhanced factor (EF) value was2.1×106with10-5mol L-1R6G as the probing molecules. Due to the great specific surface area and excellent absorption capacity of GO, the ultra thin GE films with controllable thickness were prepared by dip-coating technique. The transmittance of the ultra thin film was near90%at550nm. The film with smooth surface and fewer defects could be obtained by thermal reduction at900℃, and the obtained film showed surface resistance of40kΩ□-1. The film only performed detectable SERS activity toward the R6G molecules because only chemical enhancement existed in the GE ultra thin film. The ultra thin Ag NPs/GE films were fabricated by alternating deposition of GO sheets and Ag NPs colloid by dip-coating method. As the small thickness of the film and the Surface Plasmon Resonance of Ag NPs, the SERS activity of the Ag NPs/GE ultra thin films enhanced significantly. The EF value toward R6G molecules (105mol L-1) was up to9.1X106. The lowest probe concentration reached10"11mol L"1. More importantly, the ultra thin Ag NPs/GE films exhibited excellent SERS activity for the detecting of E. coli. In the experiment, a layer of GE sheets was deposited on the surface of Ag NPs/GE ultra thin film by dip-coating technique. The outer GE layer protected the Ag NPs from oxidation effectively and increased SERS property and stability. The EF value toward R6G molecules was increased to1.3×107. After6months storage, the EF was kept at1.2×107. The reason of the improvement of the SERS performance was discussed from the point of chemical enhancement and electromagnetic enhancement mechanism. |
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