Basics of Surface-Enhanced Raman Scattering (SERS)

Abstract

Surface-enhanced Raman scattering (SERS) spectroscopy is based on the enormous enhancement of Raman scattering of molecules adsorbed on suitable metallic (mainly silver and gold) nanostructures. Two mechanisms contribute to the total enhancement: the electromagnetic one based on resonance excitations of surface plasmons in the metal and the chemical (or molecular) one increasing the polarizability of the molecule. Average enhancement factors are about 104–106 but even values about 1011 can be achieved in some cases. This chapter will briefly introduce the basics of SERS theory and some experimental aspects of SERS (choice of metal, distance dependence, selection rules, enhancement factors, “hot spots”, single-molecule SERS, resonant SERS). The SERS substrate plays a key role in any SERS application. An overview of SERS-active substrates employed in bioanalytical, biomolecular and medical SERS applications and their properties will be discussed. It includes nanoparticles in suspension, nanoparticles assembled and immobilized on solid substrates (bottom-up approach) and nanostructures fabricated directly on solid substrate (top-down approach). The related enhancing techniques (tip-enhanced RS—TERS, shell-isolated nanoparticles-enhanced Raman scattering—SHINERS, surface-enhanced infrared absorption—SEIRA and surface-enhanced fluorescence—SEF) will also be presented.