Metastable phase-separated droplet generation and long-time DNA enrichment by laser-induced Soret effect

Spatiotemporally controlled laser-induced phase separation (LIPS) offers unique research avenues and has potential for biological and biomedical applications. However, LIPS conditions often have drawbacks for practical use. For instance, LIPS droplets are unstable and diminish after the laser is terminated, which limits their applications. In this study, we developed a novel LIPS method using the laser-induced Soret effect to generate phase-separated droplets at the laser spot in an aqueous two-phase system (ATPS) of dextran (DEX) and polyethylene glycol (PEG). When DEX-rich droplets were generated in the DEX/PEG mix of which concentrations are on the coexisting curve, the droplets showed unprecedently high longevity; the DEX droplets were retained over 48 h. Although the mechanism underlying this counterintuitive phenomenon is unclear, this observation suggests that there is an unknown metastable state. By exploiting the capability of DEX-rich droplets to enrich nucleic acid polymers, we achieved stable DNA enrichment in LIPS DEX droplets with a high enrichment factor of 1400 ± 400. Further, we patterned DNA-carrying DEX-rich droplets into a designed structure to demonstrate the stability and spatiotemporal controllability of DEX-rich droplet formation. This is the first LIPS droplet generation in a DEX/PEG system with flexible conditions for the usage of LIPS droplets and opens new venues for the biological and medical applications of LIPS.