Cellular water content governs the concentration of all biomolecules inside a cell, thereby influencing the physical and functional properties of the cell. However, measurements of water content in physiologically relevant cell culture models remain largely unavailable, particularly in three-dimensional (3D) models such as tumor spheroids and organoids. Here, we achieve such measurements using an industrial-grade capillary steel tube. The steel tube functions as a mechanical resonator that inertially senses the buoyant mass of particles. For microgram-scale particles ≥ 400 micrometers in diameter, we achieve <1% precision error in buoyant mass with a 5-minute acquisition interval. By sequentially measuring the buoyant mass of individual, patient-derived glioblastoma tumor spheroids derived from patients with glioblastoma in media of different densities and cell permeabilities, we determine the absolute and fractional (volume/volume) water content of the spheroids, along with their dry mass, volume, and density properties. We achieve ~0.5% precision error in fractional water content with a throughput of three spheroids per hour. This enables us to detect both interspheroid heterogeneity in fractional water content and acute responses to kinase inhibition. Overall, we establish a simple and accessible technique for quantifying water content in living 3D cell culture models, opening previously unexplored avenues for studying biophysical regulation in multicellular systems.
Katsikis et al. (Fri,) studied this question.