Non-invasive measurement of biomolecular condensate interfacial tension and bending rigidity

Accurate measurement of biomolecular condensates' mechanical properties is essential to understand their behavior within cells. We present FlickerPrint, an open-source Python package to determine the interfacial tension and bending rigidity of thousands of condensates using flicker spectroscopy by analyzing their shape fluctuations in confocal microscopy images. We detail the workflow and computational requirements of FlickerPrint to scale up these individual measurements to the population level. Examples of experiments in live cells and in vitro that are suitable for analysis with FlickerPrint are provided, as well as scenarios where the package cannot be used. Using these examples, we show that the results obtained are robust to changes in imaging setup, including frame rate. This implementation enables a step change in measurement capability for two key properties of biomolecular condensates: interfacial tension and bending rigidity. Moreover, the tools in FlickerPrint are also applicable for analyzing other soft, fluctuating bodies, demonstrated here using vesicles.