Live, spatially-resolved imaging of absolute intracellular water content using holotomography

Water is the predominant component of living systems, and its regulation and movement in response to stimuli is a critical feature of homeostasis. While many techniques report relative changes in the water content of cells, measuring the absolute water content in live cells is difficult. In this work, we introduce methodologies for quantifying the absolute intracellular water content using holotomography, which can be applied to unlabeled live cells of arbitrary shape. Using the volumetric and mass-sensitive nature of holotomography, we treat the cell as a two-component mixture model of solid and aqueous materials and solve for the absolute water content. We apply these techniques to quantify absolute intracellular water content of cells undergoing mitosis and responding to external stressors, including osmotic shock and pulsed electric fields, which induce rapid osmotic change. These techniques will aid in elucidating biological, chemical, and physical mechanisms of water transport.