Surface-enhanced Raman scattering for biosensing platforms: a review

The past few decades have seen rapid advances in surface-enhanced Raman scattering (SERS) techniques which have enabled increasingly efficient detection of infinitesimal molecular traces down to the single molecule. This occurrence paved the way for promising applications, among which the use of SERS in highly efficient label-free optical sensors, thus attaining a large interest, especially in the biomedical field. SERS sensors are realized following different strategies, usually involving the control of size and shape of nanoantennas and the design of nanostructures arrays to precisely set the Localized Surface Plasmon resonances (LSP) and the hot spots positions. However, this may entail the use of lithographic techniques with high fabrication costs. Other approaches are based on disordered arrays of plasmonic nanostructures, much cheaper and easier to fabricate, although the control of the hot spots position and performances is lost. Here we review the more recent SERS strategies approached in order to obtain the desired detection of analytes and specific biomolecular species, ranging from the realization of particularly efficient SERS substrates suitable for hydrated molecules to the creation of hot spots in a liquid environment enabling highly sensitive spectroscopic sensors in the natural habitat of the biomolecules.