The Research On Controllable Surface Plasmon Resonance Of Gold Nanorods In Immunoassay Application

Gold nanorods have unique optical properties, and have good prospects in medical, sensing, chemical separation and immunoassay, which become a hot topic in recent years. The anisotropy in dimensions of gold nanorods leads their surface plasmon reasonance (SPR) to split into two bands: the transverse SPR band and the longitudinal SPR band. In this thesis, three parts of works have been investigated about gold nanorods.Firstly, a series of gold nanorods with controllable aspect ratios were prepared via an improved seed-mediated technique. The longitudinal SPR were adjusted in large-scale, and inspired to achieve the maximum coupling of excitation light. This lay a foundation for the research on the correlation of optical, spectral properties and the shaope of gold nanorods.Secondly, We systematically correlate the shape-dependent SPR and SERS properties in dilute colloids. The shape-dependent SPR behavior was simulated by Gans theory and discrete dipole approximation method. The subtle influence of SPR on SERS was then demonstrated by gradually tuning the SPR wavelength through a fixed excitation line. SERS experiments and theoretically predicted electromagnetic enhancement by three dimensional finite-difference time domain method clearly demonstrate that overlapping the SPR and the excitation line maximizes the SERS enhancement. This correlation thus enables a quick diagnosis of SERS intensity by looking at the position of the SPR band.Thirdly, we choose the gold nanorod which has the strongest SERS signal for SERS-tagged immunoassay. Raman active molecule was adsorbed on the gold nanorods, forming SERS-tagged gold nanoprobes. Upon adsorption of antibody to the nanoprobes, the antibody was tagged by SERS. Through the immunoassay reactions between SERS-tagged antibody, detected antigen, and antibody supported on solid substrate (capture antibody), SERS-tagged antibody-antigen-capture antibody sandwich conjugates were formed on the solid substrate. The higher the concentration of the detected antigen is, the more the number of the gold nanoprobes on the solid substrate is. The detection limit for a single antigen component can be reached as low as 1×10^-8 mg/mL.