Engineering novel mesoscopic structures using DNA -programmed colloidal self -assembly

Anthony Ji Kim, University of Pennsylvania


Controlling interactions between colloidal suspensions has been a fascinating challenge both experimentally and theoretically. Three-dimensional colloidal crystals assembled from monodisperse colloidal particles have generated a significant interest because of their potential application as photonic band gap materials (PBG), chemical sensors, optical filters, and switches. DNA-mediated colloidal assembly offers a unique tool for controlling the range and magnitude of interparticle interaction to promote novel crystal formation. We try to delimit those conditions under which the DNA-mediated interaction gives rise to well-ordered 3-D colloidal crystals, as well as to discuss the applications, optimization, and ultimate limitations of such DNA-mediated particle self-assembly. There are many unknowns regarding the expected colloidal phase diagram and the strength and kinetics of the DNA-mediated interaction, as well as the nonspecific interactions between colloids with different surface chemistries. We start with the simplest case of one-component system, where every colloid has a DNA-mediated attraction to every other, since the phase behavior and kinetics of one-component dispersions is well understood from previous studies. We determine and model the temperature and DNA-density dependence of the self-assembly phase diagram and kinetics. We find that crystals only form with the sterically stabilized DNA-particles in a rather narrow range of temperatures and have acceptably fast nucleation and growth in a small range of grafted-DNA density. In addition, the phase behavior of binary alloy solid solutions is studied using the same sterically stabilized colloidal particles. A competition between DNA single-base mismatches is used to create energy penalties for the substitution of a few KBTs'. The minority species substitute into the crystal lattice when the pair interaction difference is a fraction of a K BT, however, they exclude from the growing crystal when the pair interaction difference becomes larger. The segregation coefficient stays the same for different starting A:B stoichiometry, proving that the substitution is an equilibrium process. Finally, we describe the assembly of binary dispersions of DNA-particles, with different size ratios, into close-packed binary alloy structures such as NaCl and CsCl. Confocal microscope is used to image different slices of the acrylamide/bis-acrylamide polymerized/DMSO solvent swapped structures to obtain crystallography of the assembled structures.

Subject Area

Chemical engineering|Materials science

Recommended Citation

Kim, Anthony Ji, "Engineering novel mesoscopic structures using DNA -programmed colloidal self -assembly" (2006). Dissertations available from ProQuest. AAI3246177.