Label-free multimodal coherent Raman and multiphoton non-linear optical microscopy for biological applications.

Optical microscopy is an extremely powerful investigation tool for life sciences, thanks to its ability of visualizing morphological details in cells and tissues on the sub-micrometer scale. Nonlinear optical (NLO) microscopy techniques, in particular, offer additional advantages, such as inherent 3D-sectioning capability and greater penetration depth, due to the use of infrared wavelengths. In this contribution, we will present our recent results in multi-modal NLO imaging applied to biological samples. Our home-built microscopes offer different contrast mechanisms: two-photon-excited fluorescence and label-free techniques such as second-harmonic generation, highlighting non-centrosymmetric structures like collagen fibers in tissue, and chemically specific coherent Raman scattering spectroscopy (including both CARS and SRS modalities) that measures the vibrational spectrum of a molecule to provide an endogenous signature that can be used for its identification. We will present applications in tumor tissue identification and the study of senescence in human tumor cells after therapy, a major cause of cancer relapse.