Toehold-Mediated Surface Modification of Colloidal Single Crystals.

Surface energy and dangling bonds are central to the chemistry of nanomaterials, yet their role in colloidal crystal engineering remains underexplored. Here, as a microcrystal-scale analogue to nanoparticle surface functionalization, we introduce a post-synthetic, surface-specific reaction to modify DNA-engineered colloidal crystals by harnessing their surface-exposed sticky ends. Using toehold-mediated strand displacement (TMSD), crystal surfaces are selectively activated without disrupting their internal lattice structures or faceted Wulff morphologies. This targeted modification enables dynamic and reversible control over surface functionality, as demonstrated by the selective attachment of larger nanoparticles and the emergence of short-range ordering in hierarchical assemblies. These findings establish TMSD as a powerful tool for the surface engineering of colloidal crystals, guiding them toward responsive, programmable matter in nanotechnology.