Spherical colloids covered with grafted DNA have been used in the directed self-assembly of a number of distinct crystal and gel structures. Simulation suggests that the use of anisotropic building blocks greatly augments the variety of potential colloidal assemblies that can be formed. Here, we form five distinct symmetries of colloidal clusters from DNA-functionalized spheres using a single type of colloidal crystal as a template. The crystals are formed by simple sedimentation of a binary mixture containing a majority "host" species that forms close-packed crystals with the minority "impurity" species occupying substitutional or interstitial defect sites. After the DNA strands between the two species are hybridized and enzymatically ligated, the results are colloidal clusters, one for each impurity particle, with a symmetry determined by the nearest neighbors in the original crystal template. By adjusting the size ratio of the two spheres and the timing of the ligation, we are able to generate clusters having the symmetry of tetrahedra, octahedra, cuboctahedra, triangular orthobicupola, and icosahedra, which can be readily separated from defective clusters and leftover spheres by centrifugation. We further demonstrate that these clusters, which are uniformly covered in DNA strands, display directional binding with spheres bearing complementary DNA strands, acting in a manner similar to patchy particles or proteins having multiple binding sites. The scalable nature of the fabrication process, along with the reprogrammability and directional nature of their resulting DNA interactions, makes these clusters suitable building blocks for use in further rounds of directed self-assembly.
Keywords: DNA; colloidal clusters; directed assembly; directional interactions; ligation.