Synthesis SERS Probe And SERS-active Substrate For Surface-enhanced Raman Scattering Immunoassay

Surface-enhanced Raman scattering (SERS) holds vast potential as a highly sensitive and selective tool for the identification of biological or chemical analytes. Its narrow, well-resolved bands allow simultaneous detection of multiple analytes, and the low intensity of SERS signal of water simplifies investigation of biological samples. The most critical aspect of performing a SERS experiment is the choice and/or fabrication of the noble-metal substrates or SERS probes. This dissertation describes the novel synthesis methods of SERS-active substrates and SERS probe, and their applications in immunoassays. The details are summarized as follows:1. An improved synthesis method of Au@SiO₂ SERS probe has been described in chapter one. The common properties of the core-shell nanoparticle-based SERS tags including Au@SiO2 are the strong SERS signal and extraordinary stability. The most exciting advantage of the method is its simplisty and time saving procedure as compared to other preparing methods reported before. Besides, the proposed methodology eliminates the use of vitrophilic pretreatment during the preparation, which is necessary in other proposed methodologies.2. In chapter two, a novel method of preparing SERS-active substrates with high sensitivity and reproducibility has been stated. Preparation of SERS substrate is always the core procedure in the surface-enhanced Raman scattering experiments. An ideally SERS substrate should generate significantly large with almost equal enhancement factor. The recent nanoparticle array studies show that the precise control of gaps in the sub-10 nm regime, known as"hot spots", is crucial for fabrication of substrate with uniformly high SERS activity for collective surface plasmons existing inside the gaps. According the discovery of Halas's research group, we managed to prepare convenient and cost-effective substrate–gold nanosphere arrays with sub-10 nm gaps to obtain high, stable and reproducible SERS signal, which enables trace-level quantitative analysis.3. In chapter three, based on the SERS-active substrate described above, we attempt to develop a novel sandwich-type immunoassay method to detect human IgG. It involves the immobilization of capture antibodies on the surface of microwell plate, the use of the immobilized antibodies to capture antigens from solution, and the indirect measurement of SERS signal of CVs that encapsulated by antibody-modified liposome. The use of substrate of gold nanosphere arrays with sub-10-nm gaps for CV SERS signal recording substantially improved the sensitivity and reproducibility as compared to conventional Ag-colloid substrates. Linear response has been obtained covering the logarithm of concentrations from 1.0×10^-8 to 1.0×10^-4g·mL^-1 with a detection limit of～8ng·mL^-1. The method holds potential applications in detection of various antigens or other clinically important entities.