The Role of Repulsion in Colloidal Crystal Engineering with DNA*

By systematically using the co-assembly of DNA-conjugated proteins and spherical gold nanoparticles (AuNPs) as a model system, we explore how steric repulsion between non-complementary, neighboring DNA-NPs due to overlapping DNA shells can influence their ligand-directed behavior. Specifically, our experimental data coupled with coarse-grained molecular dynamics simulations reveal that by changing factors related to NP repulsion, two structurally distinct outcomes can be achieved. When steric repulsion between DNA-AuNPs is significantly greater than that between DNA-proteins, a lower packing density crystal lattice is favored over the structure that is predicted by design rules based on DNA-hybridization considerations alone. This is enabled by the large difference in DNA density on AuNPs versus proteins and can be tuned by modulating the flexibility, and thus conformational entropy, of the DNA on the constituent particles. Such lattices are shown to undergo dynamic reorganization by changing salt concentration. This work help to elucidate the structural considerations necessary for understanding repulsive forces in DNA-assembly and lay the groundwork to increase architectural diversity in engineering colloidal crystals.