Visualizing three-dimensional intracellular water content using holotomography

Measurements of spatially-resolved intracellular water content are notoriously difficult, but highly desirable for studies spanning biology and biophysics. In this work, we employ the emerging technique of refractive index tomography (alternatively known as holotomography) to compute the three-dimensional, spatially-resolved distribution of water within living cells. We treat each voxel in a refractive index tomogram as a two-component mixture of dry and aqueous components, and using the average mass density of proteins, we show visualization of the 3D distribution of intracellular water in a variety of scenarios, including mitosis, growing neurons, osmotic shock, and cells responding to pulsed electric fields.