Taylor Dispersion‐Induced Phase Separation for the Efficient Characterisation of Protein Condensate Formation

Biomolecular condensates have emerged as important structures in cellular function and disease, and are thought to form through liquid‐liquid phase separation (LLPS). Thorough and efficient in vitro experiments are therefore needed to elucidate the driving forces of protein LLPS and the possibility to modulate it with drugs. Here we present Taylor dispersion‐induced phase separation (TDIPS), a method to robustly measure condensation phenomena using a commercially available microfluidic platform. It uses only nanoliters of sample, does not require extrinsic fluorescent labels, and is straightforward to implement. We demonstrate TDIPS by screening the phase behaviour of two proteins that form biomolecular condensates in vivo, PGL‐3 and Ddx4. Uniquely accessible to this method, we find an unexpected re‐entrant behaviour at very low ionic strength, where LLPS is inhibited for both proteins. TDIPS can also probe the reversibility of assemblies, which was shown for both α‐synuclein and for lysozyme, relevant for health and biotechnology, respectively. Finally, we highlight how effective inhibition concentrations and partitioning of LLPS‐modifying compounds can be screened highly efficiently. Protein phase separation (PPS) is important in functional and disease biology but is challenging to study. We present Taylor dispersion induced phase separation (TDIPS) to study PPS in a reaction‐diffusion system inside a microfluidic capillary. The resulting data is highly information‐rich and allows for thermodynamic analysis but also efficient screening campaigns of phase separation‐modulating compounds using only nanoliters of sample per data point.