Vortex-Generated Microdroplets Enable Simple, Rapid, and Low-Volume Measurement of Condensate Volume and Concentration.

Biomolecular condensates are increasingly recognized for their crucial roles in intracellular organization and the origin of life. Despite their growing importance, efficiently and accurately quantifying condensate volume and concentration remains challenging, hindering the understanding of their properties and functions. Conventional spectroscopy-based methods for measuring condensate concentration in bulk systems have practical limitations; for example, they require laborious calibration and preparation procedures, large sample volumes, and in vitro analysis. Here, we introduce a microdroplet-based method that leverages a simple and rapid vortex-assisted emulsification approach to encapsulate condensates within microdroplets. By determining the microdroplet-to-condensate size ratio and partition coefficient in situ, this method enables rapid and calibration-free quantification of molecular concentrations within condensates. Notably, it reduces processing time by more than tenfold and reduces sample volume and material cost by over two orders of magnitude, while maintaining accuracy comparable to conventional methods. Moreover, this method can precisely quantify subtle variations in condensate volume and concentration under changing environmental conditions, such as salt concentration and stoichiometries. The microdroplet-based method is anticipated to find broad applicability in fields where precise, efficient, and in situ quantification of condensate volume and concentration is critical, particularly when sample volumes are limited or environmental conditions are dynamic.