Liquid-liquid phase separation as a tool to compartmentalize stimuli-responsive cargoes within protocell models.

In this work we harness liquid-liquid phase separation to organize the internal content of protocell models based on water-in-oil droplets. Our approach is based on the spatial segregation of two polymers, polyethylene glycol (PEG) and dextran, within the aqueous phase to produce biphasic droplets. We demonstrate that magnetic field-responsive nanoparticles functionalized with dextran are preferentially sequestered within the dextran subphase. This encapsulation enables droplet heating by application of alternating magnetic fields (AMFs). Meanwhile, the PEG subphase of the droplets remains available for the encapsulation of complementary cargoes, such as PEG-coated plasmonic nanoparticles (for dual-mode heating) or an enzyme. Crucially in this latter case, we show that AMF-induced heating provided by the magnetic nanoparticles significantly enhances enzymatic activity by increasing temperature to optimal values for the enzyme. Our results demonstrate that liquid-liquid phase separation provides a route for the hierarchical organization of components within specific modules in protocell models, while simultaneously enabling tuneable functionalities.