Spatial Organization of DNA Liquids

Cells operate by compartmentalizing chemical reactions. Much recent work has shown that the spatiotemporal formation and control of membraneless compartments inside cells (liquid-liquid phase separation) is integral to cell function. Here, we investigate the dynamics and long-range structures formed by a model phase-separating DNA system. We use DNA nanostars, a system of finite-valence particles, roughly 10nm in size, whose sequence is designed such that they self-assemble into liquid droplets on the micron scale via a binodal phase transition. We find that the structure is hyperuniform, corresponding to a disordered structure with anomalously small long-range density fluctuations, which is characteristic of a spinodal decomposition process that represents a perturbation that then relaxes to equilibrium via droplet Brownian motion. In addition, we quantify the concentration and temperature dependence of the initial droplet appearance time and find that phase separation dynamics are consistent with a classical nucleation picture where droplet growth is dominated by Brownian motion and coalescence. Finally, we investigate how droplet hyperuniformity might be exploited in chemical reaction schemes, analogous to those present in biomolecular condensates, by coupling phase separation to an in vitro transcription reaction. We hope that our work on near-equilibrium droplet assembly and structure provides a foundation to investigate droplet organizational mechanisms in driven/biological environments, or to implement droplet patterns as efficient biochemical reactors.