Synthesis Of Transition Metal Core-shell Nanoparticles And Their Applications In Surface-enhanced Raman Spectroscopy

Surface enhanced Raman spectroscopy (SERS) as one of the most sensitive detection spectroscopy technology of surface species, the preparation of SERS substrate has been the most important areas of research in SERS technique. The special structure of core-shell nanomaterials has provided a high-performance material for SERS substrate. Preparation of the new composite nanomaterials of shell metal with catalytic effect and core metal with SERS effect is conducive not only to broaden the scope of the study of SERS, at the same time may also make use of high surface sensitivity of SERS to study the catalytic performance of functional transition metal. However, the transition metal and the formation of Au core-shell nanoparticles for the SERS study is limited to Au@Pd and Au@Pt, no other transition metals and Au, Ag formed the core-shell nanoparticles for SERS study. Cobalt and nickel as a wide range of transition-metal materials, in catalysis and electrochemistry fields value is very important.The core-shell nanoparticles withγ-Fe2O3 nanoparticles for nuclear and Au for shell, at the same time with the paramagnetic ofγ-Fe2O3 and high SERS activity of Au, can be used as an ideal SERS substrate material. As the outer layer of Au has the characteristics of easy modification, the stability, surface modification and biological adaptability of Fe2O3@Au core-shell nanoparticles have been significantly improved. The special features of magnetic core-shell material used in SERS substrates can be targeted and on-site inspection, in order to achieve low concentration or even single-molecule detection studies. Combine the highly sensitive of SERS and special features of magnetic materials, can be used for separation and detection of biological research, but the research is still in its initial stage, only a very small number of domestic and foreign group to carry out applied research in this regard.Based on the above idea, this paper combined the characteristics of core-shell nanoparticles with surface-enhanced Raman spectroscopy. Preparation core-shell nanoparticles with a high SERS activity and the nature of transition metal with the outer for the study of transition metal surface, such as the orientation and structure. And use the magnetic properties of core-shell Fe2O3@Au nanoparticles in the separation of antigen solution and take advantage of the high sensitivity of SERS effects of separation immunoassays. The main results of the dissertation are listed as follows:(i) Synthesis of Au@Pt core-shell nanoparticles and electrocatalytic studyAu@Pt nanoparticles of different thickness were prepared by application of the growth on gold seeds of chemical reduction of two steps, and regulate the content of gold and platinum packages available in different thickness of Au@Pt nanoparticles. Cyclic voltammetry study of 70 ~ 80nm diameter of the Au @ Pt nanoparticles shows that, the performance of the core-shell nanoparticles is similar with pure platinum. The Au@Pt nanoparticles have good electrocatalytic activity to the oxidation of methanol, and its electrocatalytic properties enhance with the increase of potential cycle scan numbers. The Au@Pt nanoparticles have special loose-shell structure, own to that the surface structure reorganization may occur on the electrochemical cycle, and an increase of its electrocatalytic activity with no change in the effective surface area.(ii) (ii) Synthesis of Au@Co and Au@Ni core-shell nanoparticles and their applications in SERSOn the basis of prepare Co and Ni nanoparticles, Co and Ni shells were prepared on the surface of Au nanoparticles by hydrazine in ethanol, and different thicknesses of Au@Co and Au@Ni nanoparticles were controlled by controlling the cobalt salt and nickel salt material. SEM, electrochemical cyclic voltammetry and SERS studies using CO confirmed the core-shell structure of transition metal nanoparticles, and the shell of the transition metal is "pinhole free".The Au@Co and Au@Ni nanoparticles dispersed on a GC electrode surface exhibit high SERS effect for the adsorbed pyridine. High-quality SER spectra of CO absorbed on Co and Ni have been obtained through the high enhancement of the core-shell nanoparticles. With the increase of the shell thickness, the SERS intensity decreases significantly, indicating the high SERS activity obtained from the ultrathin shell system is attributed to the long-range effect of the electromagnetic field of the Au core. The SERS signal of the strongest band of pyridine from the Au@Co and Au@Ni is about 60 and 200-fold stronger than that of roughened massive Co and Ni electrodes, respectively. Considering the roughness factor of the roughened electrode to be about 4.2 for Co and Ni and that of core–shell nanoparticles film electrodes to be about 15, one would expect the surface enhancement factor for the core–shell nanoparticles was evaluated at the level of 103–104. Such kind of SERS-active substrate can be used as an alternative substrate for investigating adsorption and reactions occurring on the Co and Ni metal surfaces.( iii ) Synthesis of Magnetic Fe2O3/Au Core/Shell Nanoparticles for Bioseparation and Immunoassay Based on Surface-Enhanced Raman SpectroscopyFe2O3/Au core/shell nanoparticles with different Au ratio were prepared by reducing HAuCl4 on the surface ofγ-Fe2O3 nanoaprticles. Fe2O3@ Au nanoparticles enrichment through the magnetic field, the relationship between SERS study of aggregation points and the time of imposition the magnetic field showed that the SERS signal of Py greatly enhanced after adsorption in the aggregation of magnetic Fe2O3@Au nanoparticles. Several probe molecules of different forces with Au used to study their SERS detection limit after absorbed on the aggregation of magnetic Fe2O3@Au nanoparticles. Preliminary findings show that different organic molecules with the shell Au of different forces, Fe2O3@Au nanoparticles as a SERS substrate will be different limits of detection. And as the force increase, the SERS detection limit of molecules adsorbed on aggregation of magnetic Fe2O3 @ Au nanoparticles become lower.The core-shell Fe2O3@Au magnetic nanoparticles were used for separation of antigen solution, and effect of separation was assayed based on the high sensitivity of SERS. SERS has demonstrated its ability to characterize the process occurring on metal surfaces on the molecular level. By selecting the appropriate molecular markers and a certain measure of gold nanoparticles, antigen detection limit can be achieved fg/mL in our system, provide a basis for detecting the effects of magnetic separation. Single type of antigen and multiple types of antigens in text solution both have been separated by magnetic Fe2O3/Au core/shell nanoparticles. The high separation efficiency of this effective method has shown a potential application for magnetic Fe2O3/Au core/shell nanoparticles in bioseperation.In summary, by combination of SERS and core-shell metal nanoparticles, the scope of application of SERS broaden, the SERS spectra can be used in the study of substance on the surface of transition metal. The special features of magnetic core-shell nanoparticles used in SERS substrate, not only through the target and on-site inspection to achieve low concentration or even single-molecule detection, at the same time can make use highly sensitive of SERS for biological separation and detection research.