Aromatic dyes widely exist in our environment. It is important to monitor the content of these dyes in environment as many of them are labeled as mutation, carcinogen and other toxic agents. Raman spectroscopy has been widely used for the characterization and analysis of organic molecules due to that it can provide a unique figure-print information of target molecule. By further using Au/Ag as enhancement substrate, the Raman signal of the target molecule could further amplified, and thus to achieve the sensitive detection of the target. In this thesis, several Au/Ag nanostructure or Au/Ag based hybrid structures were prepared and used as SERS substrate for the sentive detection of some typical aromatic dyes. The content manily involves:1. Surface structure of gold or silver nanoparticles plays an important role in determining its SERS enhancement ability. In chapter two, a modified approach was developed to prepare an urchin-like gold nanostructure(UGNS) by using silver nanoparticles as seed, dopa as reductant, and HAuCl4 as gold precursor. Due to the plenty of stings on its surface, the UGNS could produce more hot spots, and thus achieve a high enhancement ability. The organic coating on UGNS could be partly removed by electrochemical treatment, and thus the distance between target molecule and the gold enhancement surface was shorten, which is benefit for producing strong SERS signal. By optimizing the usage of Ag nanoparticles to tune the sizes of UGNS, we achieved optimal resonance enhancement of the material. Besides, the cycle numbler of electrochemical treatment was also optimized to elevate the enhancement effect of UGNS while retaining the urchin-like morphology. The optimized UGNS are successfully applied to SERS detection of polycyclic aromatic hydrocarbons pollutants Malachite Green with the minimum detecatable concentration of 5×10-7M.2. SERS as a tool for dye detection often displays low sensitivity due to that the target dye shows low affinity to the pristine gold or silver surface. In chapter three, a new type of ternary nanocomposite iron oxide@gold@graphene oxide(Fe3O4@Au@GO) was prepared, which is expected to enhance its adsorption ability to dye molecules, and increase the SERS sensitivity. Fe3O4@Au@GO was consisted of Fe3O4 magnetic nanoparticles, Au nanoparticles, and graphene oxide nanosheets organized in a layered structure. The ternay hybrid combined the magnetic separation and enrichment properties of Fe3O4 nanoparticles, highly electromagnetic enhancement of Au nanoparticle as well as the high adsorption to aromatic dyes and the charge-transfer enhancement of GO. After optimizing the dosage of Au nanoparticles and GO in this ternay hybrid by using crystal violet as a probe molecular, the optimized material was used as SERS detection substrate to detect dye moleculars such as Malachite Green(MG) and Nile blue(NBA) with detection limit down to 10-9-10-10 M. The Fe3O4@Au@GO hybrid was also succesfully used in SERS analysis of the mixture of MG and NBA, and determine of MG in real water sample with satifactory results.3. The composite of graphene-gold or graphene-silver is widely used as substrate for SERS detection. However, a low signal to noise ratio, and thus a relative high detection limit were obtained due to the large background noise from these hybrid substrates. Besides, the enhancement ability of graphene-Au/Ag reported in previous papers is also puzzeled. In chapter four, a composite of graphene oxide-silver(GO-Ag) was prepared by one-pot step. Then the effects of different dosage of GO-Ag, and the loading amount of Ag nanoparticles on GO nanosheets on its SERS performance for dye detection were investigated in detail. Our results indicated that the composite dosage is critical to the signal to noise ratio. Too high dosage of the composite will lead to a low siganl to noise ratio, and thus high detection limit. The sivler loading amount influence the SERS singal intensity of the target molecules. Both of too high or too low silver loading will result in weak SERS signal of target dye molecules. These rules worked for different dye molecuels and different GO-Ag composites. After carefully tailing the dosage of composite and the silver loading, and optimized GO-Ag substrate was used to achieve the sensitive SERS detection of several typical aromatic dyes with detection limit down to 0.1 uM. The results presented here are benefit to rationally understand the enhancement ability of graphene-Au/Ag substrate reported in differerent paper, and provides useful information for designing new advanced graphen-Au/Ag composite as SERS substrate. |