Figure 2. High-resolution Brillouin image of a single cell in vitro.

A cross section through a single cultured human umbilical vein endothelial cell imaged using both Brillouin (a) and phase contrast (b) microscopy at 100x magnification. Cellular structures, such as the nuclear envelope (arrow) and nucleoli (*), are clearly recognisable in both image modalities. Representative Brillouin (Anti-Stokes) spectral peaks from cytoplasm, nuclear envelope and nucleoli (c). From the Brillouin shift and the associated longitudinal modulus, it is apparent that these structures exhibit different mechanical properties compared to the surrounding cytoplasm. In particular, the nuclear envelope and nucleoli exhibit higher longitudinal moduli (2.78 ± 0.05 GPa, p < 0.0001 and 3.12 ± 0.07 GPa, p < 0.0001 respectively) than the nucleus and cytoplasm that surrounds them (2.51 ± 0.04 GPa) (values reported as mean ± s.d.). A bar-plot represents the differences (mean ± SEM) between the longitudinal modulus as measured in the cytoplasm, nucleoli, and nuclear envelope of all experiments (*p < 0.001) (d).