Surface-Enhanced Raman Spectroscopy: Applications and Methods

Surface-enhanced Raman spectroscopy (SERS) enhances Raman scattering of molecules adsorbed to a rough metal surface by several orders of magnitude, making it a valuable tool for analytical chemistry. Gold nanoparticles, ranging from 30-50 nm in diameter, are easily synthesized in the laboratory and have a long shelf-life if properly stored, making them useful for a wide array of experiments. Alone, these particles have virtually no Raman signal, but when tagged with any Raman-sensitive molecule there is an enormous molecular signal enhancement. However, molecule-coated nanoparticles often precipitate out of solution, leading to inconsistencies with analysis and data reproducibility. This problem has been overcome by glass-coating tagged nanoparticles. These shelled and tagged nanoparticles remain stable for several months, and can function as Raman reporters for more complex research applications. Antibody-adsorbed Raman reporters can be used to selectively bind an antigen of interest. When used in conjunction with antibody-adsorbed buoyant, neutrally buoyant, or paramagnetic microparticles, reporter-bound antigen can be concentrated in a sample by settling, centrifugation, or magnetic pull-down methods, respectively. Immunoassays using the three different microparticles and Raman reporters were used to detect antigen presence.