Fingerprint Raman spectroscopy for identification of hydration-dependent Brillouin shift variations in brain tumor tissue

The Brillouin shift is a measure of the longitudinal elastic modulus, which is both sensitive to changes in water content and elasticity of the solid part of cells and tissues. Raman spectroscopy can be combined with Brillouin spectroscopy to provide biochemical information. In this study, the Raman signal intensity in the fingerprint region was evaluated to extract additional information about tissue hydration and relate it to the Brillouin shift. Simultaneous and colocalized confocal Brillouin and Raman spectroscopy was performed with laser excitation at 780 nm. Solutions of relevant biomolecules (albumin and sucrose) and gels (gelatin and agarose) with different concentrations up to 30% as well as glioblastoma organoids and human brain tissue were probed, and the Raman intensity in the spectral region 800 – 1500 cm⁻¹ and Brillouin shift was investigated. A strong linear correlation was found between Raman signal intensity, mass concentration and Brillouin shift for all analyzed solutions and gels, while different mixtures with the same total concentrations had similar Raman intensities. Different degrees of correlation were found between Brillouin shift and Raman intensity on GBM organoids, human brain tissue (epileptic hippocampus) and brain tumor (meningioma), indicating different contributions of tissue hydration and biomechanics to the Brillouin shift. In conclusion, combining fingerprint Raman spectroscopy with Brillouin microscopy is not only useful for extracting biochemical information that highlights changes in Brillouin parameters, but may also provide insight into the effects of local hydration driving the changes of Brillouin shift. • Local tissue hydration can strongly influence the Brillouin shift of brain tumors. • Linear relationships exist between concentration, Raman intensity and Brillouin shift. • Raman spectroscopy helps discerning contributions of tissue hydration and elasticity.