Patrice Donfack

• Light scattering is the simplest and most common scenario where incident light with a certain energy or color corresponding to a given frequency, is bounced o any object or particle in all directions. While most of this scattered light appears unchanged (having the same color), Raman scattering represents a very small portion of the scattered light that has different colors corresponding to many components with frequencies different from that of the incident light. The Raman shifts, or the frequency differences observed in Raman scattering, represent the corresponding amounts of energy that are exchanged between a material system and the light incident on it, and which can fit into possible transitions within the material system. Therefore, the collection of all Raman shifts (Raman spectrum) for a given material are characteristic of the material properties, providing a way to identify and/or discriminate different molecular systems. The Raman process, as just defined, is linear, and is termed resonant Raman if the incident light frequency matches that of an electronic transition in the molecule, or surface enhanced Raman if the irradiated molecule is in close contact with a rough metal surface. Nonlinear Raman scattering involves multi-photon interactions. In this thesis, Raman spectroscopy is applied as a noninvasive and nondestructive tool for the investigation of biological systems including biomolecules, cells, and tissue, both in vivo and in vitro. In particular, this thesis addresses key biological events such as cancer transformation and development, biological rhythm and hormonal deregulation, Hsp70 phenotypic variation and chaperon properties, and therapy response. In addition, a simple fabrication of special metallic nanoparticles and the interaction of a simple biomolecule at metal substrates are also covered. Combining different Raman techniques, the focus is not only to demonstrate the diagnostic capability of Raman spectroscopy for cancer and/or other pathological conditions. It is also directed toward noninvasive targeting of disease biomarkers for a possible understanding of the molecular basis of disease onset and development. First, using a model cell line for skin carcinoma, it is demonstrated that Raman scattering not only can help to discriminate healthy skin keratinocytes from their cancerous counterparts, but also can provide molecular insights into genetic instabilities in the human keratinocytes cells HaCaT. Furthermore, the potential for Raman monitoring of lymphoma incidence and histological subtypes in subjects at risk is evaluated using spleen tissue of a lymphoma mouse model. Another animal model (Djungarian hamsters) is used to test Raman spectroscopy as an approach for the study of the biological rhythm associated with rhythmic hormonal regulation of the reproductive system in photoperiodically sensitive breeding mammals. This work highlights the possibility for noninvasive and nondestructive phenotypic sorting of cells sublines. In this respect, Raman microscopy has been used to gain specific insights into intracellular mechanisms leading to Hsp70 chaperon properties and associated phenotypic variation in colon carcinoma sublines. Additionally, in situ Raman monitoring of drug response has been achieved in this work. Finally, it is shown that biocompatible metal nanoparticles with specific geometry, and promising for molecular targeting, can be easily and reliably fabricated. Surface enhanced Raman studies on the simplest amino acid glycine reveal that, proteinaceous compounds can behave and interact in a complex concentration-dependent manner at metal interfaces. In this respect special designs for the fabrication of nanometal substrates can be beneficial for surface enhanced Raman investigations of biological systems.