Colloidal crystal engineering with DNA can be used to realize precise control over nanoparticle (NP) arrangement. Here, we investigate a case of DNA-based assembly where the properties of DNA as a polyelectrolyte brush are employed to alter a hybridization-driven NP crystallization pathway. Using the coassembly of DNA-conjugated proteins and spherical gold nanoparticles (AuNPs) as a model system, we explore how steric repulsion between noncomplementary, neighboring NPs due to overlapping DNA shells can influence their ligand-directed behavior. Specifically, our experimental data coupled with coarse-grained molecular dynamics (MD) 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. At intermediate ligand flexibility, the crystallization pathways are energetically similar, and the structural outcome can be adjusted using the density of DNA duplexes on DNA-AuNPs and by screening the Coulomb potential between them. Such lattices are shown to undergo dynamic reorganization upon changing the salt concentration. These data help elucidate the structural considerations necessary for understanding repulsive forces in DNA-mediated assembly and lay the groundwork for using them to increase architectural diversity in engineering colloidal crystals.
Keywords: DNA; colloidal crystals; nanomaterials; nanoparticle superlattice; protein assembly; self-assembly.