Opto-mechanical material characterization via dual-geometry Brillouin confocal microscopy

Brillouin scattering is a light-matter interaction that induces a frequency shift in the scattered photons. Such shift directly depends on the optical and mechanical properties of the material itself. In the last decade, Brillouin frequency shift has become a reliable proxy for mechanical stiffness in biological samples such as cells and tissues, with the subsequent development of Brillouin confocal microscopy; however, such correlation does not apply to samples with high degree of inhomogeneity. Recently, we showed that a dual geometry Brillouin microscopy enables the direct measurement of refractive index and speed of sound. We now report an improved dual-geometry microscopy technique that allows measurement of optoacoustical properties within a confocal volume. This goal has been achieved through the measurement of frequency, linewidth, and intensity of Brillouin components of the scattered light spectrum. Finally, we proved our three-dimensional imaging capability by mapping, with micron-scale resolution, the refractive index, density, and viscoelastic properties of a liquid-liquid phase separation system. This technique can be applied to a multitude of biological heterogenous scenarios such as nucleolus characterization, high concentration lipid sites, dynamic protein aggregates and more.