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

McGinley, J. T. III, University of Pennsylvania
Crocker, J. C., University of Pennsylvania
Sinno, T., University of Pennsylvania
Jenkins, I., University of Pennsylvania

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.