Altering DNA-Programmable Colloidal Crystallization Paths by Modulating Particle Repulsion

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.