(176a) Engineering Novel Colloidal Crystal Structures Using DNA-Mediated Self-Assembly

The specific binding of complementary DNA strands is used to create short-range attractive interactions between DNA-grafted micron-sized colloids. These colloidal interactions will create multi-component colloidal mixtures where the interactions between each component are independently programmed. In theory, this technique should be able to produce well-ordered 3-D BCC, SC and diamond structures, as well as their alloy counterparts, the CsCl, NaCl and ZnS structures, all at densities near close-packing. We have synthesized sterically stable DNA-grafted particles using a novel solvent swelling/deswelling technique. PEG chains provided this extra steric stability. These particles showed temperature dependent phase behavior and they also aggregate/dissociate reversibly with temperature. In addition, we have successfully assembled first colloidal crystal structures using them. The crystal structures showed a faceted shape that resembles the RHCP stacked colloidal crystals. The colloidal crystals melted immediately when the temperature was raised above the melting temperature (Tm), confirming that they were formed and held together by DNA hybridization. We show experimentally that particle crystallization kinetics become faster as the grafted DNA density was increased. We also investigate binary alloys, such as NaCl and CsCl superlattices, assembled using DNA-mediated colloidal self-assembly. In addition, we have developed a technique to obtain 3-D confocal microscope image of these crystals by fixing them in place using UV initiated polymers.