(450f) A Diversity of Crystals and Clusters with DNA Colloids

DNA is a versatile tool for directing the controlled self-assembly of nanoscopic and microscopic objects. The interactions between microspheres due to the hybridization of DNA strands grafted to their surface have been measured and can be modeled in detail, using well-known polymer physics and DNA thermodynamics.  Knowledge of the potential, in turn, enables the exploration of the complex phase diagram and self-assembly kinetics in simulation. In experiment, at high densities of long grafted DNA strands, and temperatures where the binding is reversible, these systems readily form colloidal crystals and colloidal clusters having a range of symmetries.  For interactions that favor alloying between two different-sized colloidal species, experiments yield a variety of ionic crystal type structures and surprisingly complex superlattice structures.  We will discuss the crystallography of these structures, the transformations they undergo, as well as their relative free energies and nucleation.  Selectively ligating DNA strands allows a library of symmetric building block clusters to be created from these crystals, and these display directional bonding characteristics.