(665c) Driving Crystal Transformations and Assembling Colloidal Clusters Via Reprogrammable DNA Interactions

DNA-coated polymer microspheres have proven to be versatile building blocks for the study of directed self-assembly. DNA-directed self-assembly is governed by a multi-dimensional phase diagram, controlled by an nxn matrix of specific interactions between n species. A previous study demonstrated that the "as nucleated" crystal structure is not necessarily the minimum free-energy structure for the system. Transformations from the nucleated crystal structure to the ground state structure can occur if a suitable pathway exits between them. We show that the addition of competitive, soluble DNA strands to the system can reprogram the initial interaction matrix, and define a new minimum free energy configuration, thus driving a desired transformation. Using this concept, I have been able to reprogram both BCC and FCC crystal structures, by selectively destroying bonds, to produce high yields of colloidal clusters, consisting of a single particle surrounded by 8 or 12 particles, respectively. The clusters are initially formed as cubes (for BCC) and cuboctahedron (for FCC), but upon annealing they undergo transformations to the lower free energy structures of skew-cubes and icosahedron, respectively. We also employ reprogrammable interactions to drive reversible crystal transformations between FCC and BCC structures, with each transformation being accomplished simply by the addition of a soluble DNA strand.