Phase separation in crowded micro-spheroids: DNA–PEG system

Living cells are characterized as micro-vesicles encapsulating highly crowded macromolecular media, including DNA. To probe the intrinsic property of such crowded systems in a micro-closed environment, we observed a mixture of DNA and hydrophilic polymer, PEG within an aqueous micro-spheroid. It was found that the mixture causes phase-segregation by depositing DNA near the spheroid surface, whereas corresponding bulk solution sustains isotropic phase. After the phase segregation, DNA molecules in the condensed phase exhibit time evolution to an ordered state. This surface-mediated segregation is discussed in terms of the depletion effect under micro-confinement.