Particle levitation tensiometry (PLT) for probing interfaces of liquid–liquid phase separation systems (LLPSs)

Abstract

We introduce a particle levitation tensiometry to accurately quantify ultra-low interfacial tensions in liquid–liquid phase separation (LLPS) systems, crucial for understanding the structure and dynamics of membrane-less organelles in biological cells. Our technique uses non-reactive spherical microparticles to balance gravitational and interfacial forces, providing precise, repeatable, and reliable measurements across a wide range of LLPS systems, including aqueous two-phase systems, coacervates, and immiscible oil–oil systems. By adjusting the Bond number through variations in the bead size and density, our method allows for accurate interfacial tension measurements across values as low as 0.37 μN/m with minimal deviation and efficiently detects substantial variations in interfacial tensions with changes in compositions, concentrations, and ionic strengths; for instance, it recorded a change from 7.34 μN/m at a polyelectrolyte concentration of 0.002 M to 8.26 μN/m at 0.003 M. Our findings offer insights into the dynamics of LLPS and open pathways for applications in fields where accurate interfacial tension measurement is crucial, enhancing our understanding of cellular processes and enabling practical applications in drug delivery, adhesives, and coatings.