Correlative all-optical quantification of mass density and mechanics of sub-cellular compartments with fluorescence specificity

Research output: Contribution to journalResearch articleContributedpeer-review



Quantitative measurements of physical parameters become increasingly important for understanding biological processes. Brillouin microscopy (BM) has recently emerged as one technique providing the 3D distribution of viscoelastic properties inside biological samples — so far relying on the implicit assumption that refractive index (RI) and density can be neglected. Here, we present a novel method (FOB microscopy) combining BM with optical diffraction tomography and epi-fluorescence imaging for explicitly measuring the Brillouin shift, RI and absolute density with specificity to fluorescently labeled structures. We show that neglecting the RI and density might lead to erroneous conclusions. Investigating the nucleoplasm of wild-type HeLa cells, we find that it has lower density but higher longitudinal modulus than the cytoplasm. Thus, the longitudinal modulus is not merely sensitive to the water content of the sample — a postulate vividly discussed in the field. We demonstrate the further utility of FOB on various biological systems including adipocytes and intracellular membraneless compartments. FOB microscopy can provide unexpected scientific discoveries and shed quantitative light on processes such as phase separation and transition inside living cells.


Original languageEnglish
Article numbere68490
Number of pages23
Publication statusPublished - 10 Jan 2022

External IDs

PubMed 35001870
WOS 000758043100001
ORCID /0000-0003-4017-6505/work/142253805


Research priority areas of TU Dresden

DFG Classification of Subject Areas according to Review Boards


  • Brillouin microscopy, HeLa cells, Human, density measurement, mechanical properties, optical diffraction tomography, phase transition, Density measurement, Optical diffraction tomography, Mechanical properties, Phase transition, Cells/cytology, Humans, Tomography, Optical/methods, Fluorescence, Intracellular Space, Microscopy/methods, Refractometry, HeLa Cells, Cell Nucleus