Center for Functional Nanomaterials Seminar

The specific binding of complementary DNA strands has been suggested as an ideal method for directing the controlled self-assembly of microscopic objects. Using an optical tweezer method, we have directly measured the attractive interaction and dynamics between DNA-grafted colloidal microspheres. The interactions measured can be modeled in detail using well-known statistical physics and chemistry, without empirical corrections, boding well for their application to directed self-assembly. At high densities of long grafted DNA strands, and temperatures where the binding is reversible, these systems readily form colloidal crystals that display a range of phenomena that resemble those in atomic materials. A study of host/impurity segregation in solid-solution type crystals allows us to probe the crystal growth kinetics, confirming the validity of our interaction model. For a different system with interactions that favor alloying between two species, we find different equilibrium binary phases, two of which are found to interconvert via diffusionless transformation akin to the Martensitic transition in iron. Our observations closely resemble corresponding particle level simulations, suggesting a rational approach to designing new particle composite structures.