Label-free imaging of small lipid droplets by femtosecond-stimulated Raman scattering microscopy

In this paper, the implementation and main realization issues of a stimulated Raman scattering (SRS) microscope, obtained by the integration of a femtosecond SRS spectroscopy set-up with an optical microscope equipped with a scanning unit, are described. In order to characterize capabilities and limitations of SRS microscope, the optical resolution is measured and validation tests on polystyrene beads imaging are reported. In addition, taking account of strength of SRS vibrational contrast, label-free imaging of small biological structures, as such as lipid droplets (LDs), in adipocyte cells is carried out. The visualization of small LDs, with dimensions comparable to the optical lateral resolution of our system, is demonstrated.