Quantification\nof Biomolecular Condensate Volume Reveals\nNetwork Swelling and Dissolution Regimes during Phase Transition

Accurate determination of biomolecular condensate volume\nreveals\nthat destabilization of condensates can lead to either swelling or\nshrinking of condensates, giving fundamental insights into the regulation\nof the volume of cellular condensates. Determination of the volume\nof biomolecular condensates and coacervate protocells is essential\nto investigate their precise composition and impact on (bio)chemical\nreactions that are localized inside the condensates. It is not a straightforward\ntask, as condensates have tiny volumes, are highly viscous, and are\nprone to wetting. Here, we examine different strategies to determine\ncondensate volume and introduce two new methods, with which condensate\nvolumes of 1 μL or less (volume fraction 0.4%) can be determined\nwith a standard deviation of 0.03 μL. Using these methods, we\nshow that the swelling or shrinking of condensates depends on the\ndegree of physical cross-linking. These observations are supported\nby Flory–Huggins theory and can have profound effects on condensates\nin cell biology.