Prospects for plasmonic hot spots in single molecule SERS towards the chemical imaging of live cells

Single molecule surface enhanced Raman scattering (SM-SERS) is a highly local effect occurring at sharp edges, interparticle junctions and crevices or other geometries with a sharp nanoroughness of plasmonic nanostructures ("hot spots''). The emission of an individual molecule at SM-SERS conditions depends on the local enhancement field of the hot spots, as well as the binding affinity and positioning at a hot spot region. In this regard, the stability of near-field nano-optics at hot spots is critical, particularly in a biological milieu. In this perspective review, we address recent advances in the experimental and theoretical approaches for the successful development of SM-SERS. Significant progress in the understanding of the interaction between the excitation electromagnetic field and the surface plasmon modes at the metallic or metallic/dielectric interface of various curvatures are described. New knowledge on methodological strategies for positioning the analytes for SM-SERS and Raman-assisted SERS or the SERS imaging of live cells has been acquired and displayed. In the framework of the extensive development of SM-SERS as an advancing diagnostic analytical technique, the real-time SERS chemical imaging of intracellular compartments and tracing of individual analytes has been achieved. In this context, we highlight the tremendous potential of SERS chemical imaging as a future prospect in SERS and SM-SERS for the prediction and diagnosis of diseases.