Raman or/and surface-enhanced Raman? Advantages and limitations when applied for confocal multispectral imaging with living cells

The in situ investigations of living cells are among the most exciting biomedical applications of the confocal multispectral imaging (CMSI). The latter is often noted as chemical imaging since provides structurally specific (particularly with Raman) information. This allows non-invasive mapping of molecular composition of the cells or intracellular distribution of small Raman-active chromophores such as drugs, ion-markers, etc. Here, we attempt a comparative analysis of the major advantages and limitations of surface-enhanced Raman (SER) and non-enhanced (spontaneous and resonance) Raman techniques as used for intracellular CMSI. Based on our experimental observations and on recent data from literature we conclude that, depending on application, the differences between the two methods can be dramatic and a choice of the proper approach is imposed during acquisition, treatment and interpretation. Moreover, while Raman and SER signal can be present on the same image, these however should be treated separately, in the different way. We discuss particularities of the mapping algorithms we use to generate Raman/SER images. Concerning SER, we compare different SER-active substrates in terms of imaging on cells, taking into account both principal (short-range/long-range enhancement of the Raman scattering) and practical (simplicity of preparation and manipulation) questions.