Linker-mediated binding of DNA-grafted colloids: New phase diagrams and how to predict them*

DNA is a promising tool for programming the self-assembly of new materials: its interactions are chemically specific, tunable, and predictable. However existing approaches rely on direct hybridization of DNA strands grafted to colloidal particles and thus are too limited in their design space to create some of the more interesting structures, such as aperiodic materials or systems comprised of hundreds of unique particle species. In this work, we explore an alternative paradigm in which particles interact through DNA strands dissolved in solution instead of through direct binding of grafted strands. We find that the phase behavior that emerges in our linker-based system is surprisingly rich, exhibiting a re-entrant melting transition at high linker concentrations and a region of stable coexistence between solid and fluid. We reproduce our observations quantitatively using an equilibrium statistical mechanical model, which takes as inputs the linker concentration, grafting density, and DNA sequences. Going forward, we expect that these linker-based systems could present other interesting possibilities, like new kinds of interactions whose specificity depends on temperature.