Scanning probe microscopy elucidates gelation and rejuvenation of biomolecular condensates

A comprehensive understanding of the dynamics and solidification of biomolecular condensates is closely tied to analysis of their mechanical characteristics. Despite recent technical advances in rheological studies of condensates, these still vastly rely on methods restricted to small forces, rendering measurements of droplets with higher elasticities and after transition to solids challenging. In this work, we develop assays for in-depth mechanical characterization of biomolecular condensates by scanning probe microscopy. We demonstrate this technique by measuring the rheological behavior of heterotypic poly-L-lysine heparin condensates, showcasing their multi-route transition from liquid-like to gel as well as their rejuvenation by chemical alterations of the medium. Due to the widespread application of scanning probe microscopy in biological fields, its capability for rapid, high-throughput, high-force range studies, and integration with nanoscale morphological measurements, our probe-based method is a significant step toward advancing the understanding of condensate behavior, leading to accelerated development of therapies.