Shape-controlled Growth of Two-dimensional Colloidal Crystals through DNA-mediated Nanoparticle Capping

Organic capping ligands can selectively bind to crystal facets to modulate growth kinetics and are essential in the chemical synthesis of inorganic nanocrystals. Using capping ligands for the shape-controlled growth of colloidal crystals is challenging due to the size mismatch between molecules and nanoparticle building blocks. In existing synthetic pathways, colloidal crystal shapes are determined by their thermodynamically favored phases, yet controlling their shapes independently of the lattice symmetry is vital for studying many solid-state properties. Here, we develop a DNA-mediated nanoparticle capping strategy to control the shapes and structural heterogeneity of the colloidal crystals. Rhombohedral colloidal crystals assembled from Au pentagonal bipyramids driven by DNA hybridization were used as a model system. In the (111) planes of the crystals, bipyramids are assembled into kagome lattices, featuring structure cavities organized in a hexagonal lattice. The rhombohedral crystals exhibit truncated tetrahedral crystal habits, with the degree of truncation determining the exposed facets and crystal shapes. Our surface capping strategy involves introducing Au–DNA conjugate nanospheres as effective capping agents, which selectively bind to the surface vacancies of the kagome facets and mimic the role of organic ligands in classic nanocrystal growth. Such selective capping is driven by maximizing DNA hybridization, resulting in slower growth of the (111) kagome facets and a change in crystal shape from three-dimensional truncated tetrahedra to two-dimensional layered microplates with structural heterogeneity and shape anisotropy. This study highlights the importance of capping agents in colloidal crystal growth and proposes effective methods for controlling the growth kinetics and heterostructures of colloidal crystals.