Scanning probe microscopy elucidates gelation and rejuvenation of biomolecular condensates

Comprehensive understanding of dynamics and disease-associated 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 solid challenging. Here, 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 liquid to gel transition, as well as their rejuvenation by chemical alterations to the medium. Due to the wide-spread 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 breakthrough in investigating condensate behavior, leading to accelerated development of therapies.