Near-Infrared Excited Surface-Enhanced Raman and Hyper Raman Scattering for Microscopic Mapping of Biosamples

The chapter will discuss spontaneous, non-resonant and resonant plasmon-enhanced Raman scattering for the characterization of microscopic samples based on multi-photon excitation. Surface-enhanced hyper Raman scattering (SEHRS), the two-photon analogue of surface-enhanced Raman scattering (SERS) can be used to characterize cells and other microscopic objects based on vibrational information of reporter molecules. A combination of SERS and SEHRS is particularly interesting for the construction of nanosensors that can be used in complex biological environments to measure pH. The combination of SERS and SEHRS spectra excited at 1064 nm allows more robust pH sensing than SERS measurements in the visible or NIR excitation range alone. As another aspect, hyperspectral mapping of microscopically heterogeneous samples using SEHRS spectra is demonstrated. Combined SEHRS /SERS hyperspectral imaging by multivariate analysis can be developed into a useful imaging modality for microscopic biological samples such as cells and tissues.