A review on surface-enhanced Raman scattering

Surface enhanced Raman scattering has become a powerful tool in chemical, material and life sciences, owing to its intrinsic features (i.e. fingerprint recognition capabilities and high sensitivity) and to the technological advancements in the instrumentation that have lowered the costs, improved the performance and made it available also for non-specialized users. In this review, the origin of the SERS enhancement is described. Afterwards, the key factors that determine the enhancement of a SERS substrate are discussed: the materials, the morphology (the crucial role played by the hot spots) and the analyte-surface distance. Several fabrication strategies of SERS substrates are presented, as well as some practical issues related to their use (i.e. the measurement of the enhancement, the factors affecting the choice of the excitation wavelength in a SERS experiment, the desired features of SERS substrates for applications, the coupling of SERS with separation and capturing techniques). Finally, a representative selection of applications in the biomedical field, with direct and indirect protocols, is provided.