Surface-enhanced Raman Spectroscopy Based Magnetic Separation And Immunoassay

Magnetic composition with Au shell has been used for magnetic separation and detection in many different fields due to the well established surface modification and functionalization, surface enhanced optical properties and the magnetism of the core. The Au shell with appropriate thickness could contribute giant surface enhanced Raman scattering (SERS) activity which exhibited high sensitivity and provided rich structural information. Immunoassay with high specificity is a powerful tool for biological analysis. The combination of those advantages of SERS, magnetic separation and specificity analysis of the immunoassay enable us develop new powerful ways for specific separation and high sensitivity detection.Based on the above facts, we prepared new composition materials combined all above mentioned advantages for the immunoassay. This paper was focused on the following issues:(1) Water-soluble paramagneticγ-Fe₂O₃@Au and Fe₃O₄@Au core@shell nanoparticles have been prepared with different approaches, and the features were characterized by different techniques, and the surface modification and functionalization were performed to obtain immuno-magnetic core-shell nanoparticles.(2) A novel method called as magnetic separation immunoassay was developed. The immuno-γ-Fe2O3@Au and MBA-labeled immunogold were linked by target antigens, and combined with magnetic separation to achieve the high sensitivity detection of target antigen. The specificity, detection limits and sensitivity of this method were investigated Comparing with the conventional SERS-based "sandwich" structure immunoassay, the detection limit of this method increased 10 times, i.e. reached at 1fg/mL.(3) Three-component mixed antigens were separated by magnetic separation immunoassay. Through the specific interaction between antigen and antibody, the antigens was separated one by one, two antigens or three antigens were separated together and two-components mixed antigens with different concentrations were separated successfully. The results showed that the reported method has been achieved to separate any components in the solution with three antigens without any influence on the coexistence of other antigens. The concentration of the separated antigen was reduced to the detection limit of SERS-based immunoassay which could reach about 0.1pg/ml.(4) Developed SERS based competitive immunoassay for the detection of Hg²⁺. By the competitive interaction between the Hg²⁺ involved in the antigen and the free Hg²⁺ in solution, the semi-quantitative detection on the Hg²⁺ was achieved through the decrease in the SERS intensity of the reporter. We also investigated the effects of other ions on the detection of Hg²⁺. The method has high sensitivity, high specificity and low detection limits, and it will be developed as a novel detection method specific compound with high sensitivity.