DNA nanostars that self-assemble into core-shell condensate microdroplets

Abstract

Phase-separating DNA condensates have a range of potential uses, from synthetic cells microreactors, uniquely combining programmable nanoscale subunits with tuneable microscale properties. However, DNA condensates are inherently unstable, leading to dynamic heterogeneity and uncontrolled mixing, limiting their ability to control complex reaction pathways. Here, we develop multi-layered DNA condensate 'droplets' composed of DNA nanostars, where nanostars with different DNA sequences form distinct core and shell regions.Nanostar properties were first explored to understand how structural changes in geometry, valency, and interaction strength affect droplet phase-separation temperature, size, stability, and permeability. We show that when pairs of nanostars self-assemble in the same solution, the order of phase-separation determines core or shell destination, whereas the proportion of surfactant nanostars that link the two populations determines shell morphology. Testing 50 different nanostar combinations, we found that membrane-like systems, where the shell fully encloses the core, form if the difference in phase-separation temperatures of the two nanostars is greater than 3 ^oC with 16-25% surfactant nanostars. For 3 different core nanostars, we demonstrate a range of shell nanostars with different material properties and morphologies. Core-shell droplets have well-defined size, stability over time, and core permeability is controlled by shell properties. Furthermore, droplet size and membrane thickness were controlled by adjusting the thermal annealing rate during assembly. These techniques provide a diverse library of droplets suitable to be used as microscale reaction compartments, with predictable size, mono-dispersity, membrane thickness, and permeability. We envision that core-shell DNA nanostar droplets will open new avenues for assembling programmable materials that combine DNA condensates with DNA molecular circuits, exploiting cell-like properties such as compartmentalisation and controlled transport to achieve programmable synthetic micro reactors.