Preparation And Studying Property Of Micro/Nano Structure SERS Substrate

Raman scattering is a kind of scattering phenomenon, the frequency of the photon will be changed when the incident lights and the molecules interacted with each other, also called the Raman effect. The Raman scattering spectroscopy shows not only the natural frequency of the molecular vibrations, but also the symmetry and internal forces of molecules. Due to these reasons, Raman spectra is usually called "fingerprint spectrum". However, in the primary stage of development, Raman spectra is generally only as a supplementary part of the infrared spectrum mainly used for identification and analysis of organic molecules. Because that the Raman scattering process of molecules is very weak. For general molecules, its cross section of Raman scattering is tens orders of magnitude lower than that of fluorescent scattering. This will directly cause the phenomenon that the intensity and sensitivity of Raman signal of the material could not reach the requirements in application. Therefore, the SERS has become a key point in the scientific research. It not only retain the advantages of the Raman scattering, but also extend the application field of Raman scattering. Fundamentally, on the one hand, SERS spectroscopy technique is due to both EM and Chemical enhancement. EM is caused by the material molecule adsorption on the surface of the rough precious metals and the Chemical enhancement is caused by charge transfer between the molecule and substrate. Both the two reasons gives the result that the Raman signal can enhance. SERS enhancement effect can be represent by enhancement factor (EF). The EF can usually gets to 103?107. Used as a result, the SERS spectroscopy has a very high sensitivity and selectivity and can be a powerful way to realize qualitative and quantitative detection. Due to the advantages, the application of Raman spectroscopy got more extensive attention and overcome the problem of low signal intensity.SERS technology has many advantages. These advantages make the SERS spectrum technology be widely applied in many fields. At present, SERS spectrum technology is widely used in micro trace detection of poisonous and harmful material, real-time monitoring of chemical reaction process, and detection of biological and material life in the field of biology. At the same time, the development of micro/nano technology provide the possibility for preparation of a variety of SERS substrates which have a variety of morphology and have high stability and good performance. Now, the main direction for SERS research includes:explanation of the adsorption behavior; functional decoration of substrate and specific binding to use it in the field of research.; exploring and explaining SERS enhancement mechanisms from two aspects containing theory and experiment.In this paper, considering the application in trace detection of the toxic and harmful substances and detection of biological molecular, several micro/nano structure SERS substrate have been designed which have high density of "hot spots":ZnO-Nanocomb decorated with Ag nanoparticles (ZnO-NC decorated with AgNPs), Ag@Au core-shell dendrites and single-stranded DNA (ss-DNA) decorated on the surface of the Ag@Au core-shell dendrites to use as a specific substrate. At the same time, we assemble dimers connecting by DNA and two gold nanoparticles (NPs) to study the properties of the hot spots. Exploring the change of the properties from not only the theory but also the experimental results. In this paper, we test and characterize detailedly for the three kinds of substrates about their morphology structure, SERS property, repeatability, performance of application in many fields, enhancement machaniam and so on. Discuss and analysis in detail with the result of the experiment. Research content can be found as follows:Firstly, preparation of ZnO-NC decorated with AgNPs substrate, Ag@Au core-shell dendrites substrate and gold nanodimers (GNDs).First of all, preparation of different substrates used different experimental methods. Both the methods have advantages and disadvantages. When choose the substrate, many reasons should be considered containing the preparation methods, the structure of the substrate, the SERS property of the substrate and so on. Preparation of ZnO-NC decorated with AgNPs substrate involved a variety of experimental methods, such as:hot water corrosion, chemical vapor deposition (CVD), and impregnation-chemical reduction method, the whole experimental methods are complicated. These method can get a substrate which has better systematicness, good reproducibility of Raman signal. Ag@Au core-shell dendrites substrate has a more simple method to make it and has more rule regular array structure. While, the Au nanofilm coated on the surface of the dendrites can guarantee the substrate having good stability and biological compatibility. To explain the change of the SERS intensity of "hot spots" in theory, GNDs were designed, the SERS signal molecule was modified at different locations between the two gold nanoparticles and the SERS intensity would be changed at the same time. Using the method of Finite Difference Time Domain (FDTD), we can verify the reliability of the results with both theory and experiment.Secondly, several kinds of SERS signal molecules were used including: Rhodamine 6G (R6G), Crystal violet (CV) and some pollutants such as heavy metal ions Cd2+. Testing and analyzing the SERS spectra and considering the performance of enhancement, stability, the quantitative relation curve, and the reusability. In view of the systematic test results, we give a detailed discussion and analysis and determine the different application of the substrates.Thirdly, research of SERS enhancement mechanism. According to the microstructure of the substrate, using the method of FDTD to simulate the feature of the structure. The change of space distribution of electromagnetic of this substrate can be obtained over time. According to the results, we can see that enhancement areas of electromagnetic field generally called "hot spots" are the main sources of SERS signals. In order to understand the change of intensity of the SERS signals because of the change of position, we designed the GNDs to form the areas of "hot spots". The further understanding of the 'hot spots" is helpful for us to design new substrate and to know the effect of SERS signals according to the change of the spacing, size, the position of the signal molecules and so on.