Qualitative evaluation of a VIPA-based Brillouin spectrometer with applications to in vitro tumor tissues
Résumé
Spectrometers based on the virtually imaged phased array (VIPA) technology have been largely used for Brillouin light scattering (BLS) measurements in biological samples in the last ten years due to their fast acquisition capabilities [1-2]. In this work we assess the performances of such a commercial VIPA-based Brillouin spectrometer for drug screening applications on multicellular spheroids [3]. To identify acquisition parameters, we measured signal-to-noise ratio as a function of dwell time and laser power for a pure water sample. To define a standardized procedure for the evaluation of the spectrometer, we probed saline solutions with different concentrations. From these results, we estimate the precision, accuracy and repeatability of the device. We compare these characteristics with those of a commercial Fabry-P�rot interferometer. We then use the VIPA spectrometer to probe the sound velocity of colorectal multicellular tumor spheroids (MCTS) in the GHz range and we compared the results with the sound velocity measured using laser ultrasonic technology in the MHz range. Our results show a frequency dependence of the sound velocity, and highlights the important role of viscosity in BLS measurements in biological tissues. This suggests that existing theories based on water content [4] should be upgraded for a better understanding of tumor physics. References: [1] G. Scarcelli et al, Nat. Photonics, 2, p39-43 (2008) [2] G. Scarcelli et al, Nat. Methods, 12, p1132 (2015) [3] J. Margueritat et al, Phys. Rev. Lett., 122, p018101 (2019) [4] P. Wu et al, Nat. Method, 15, p561-562 (2018).