This project will develop techniques to engineer suspensions of DNA-labeled microspheres that will spontaneously self-assemble into novel, 3-dimensional colloidal crystal structures. The self-assembly of the spheres will be driven by a short-ranged, reversible attractive interaction induced by large numbers of very weakly associating single-stranded DNA molecules bound to their surface. Importantly, this interaction is determined by the sequence of the DNA molecules--enabling the creation of binary and ternary colloidal mixtures where the interactions between the different sphere populations are independently programmable in magnitude and sign, attractive or repulsive. This flexibility will permit the creation of previously unobserved alloy phases, such as BCC, SC and diamond-like phases, which are of interest both as model systems for atomic crystals and phase transitions as well as 3D templates for photonic bandgap crystals. Over the long-term, the goal is to produce and disseminate automated design tools for generating DNA recipes yielding a desired crystal structure. In addition, this work will provide chemical engineering students outstanding opportunities to pursue basic materials research, as well as master techniques ranging from microscopy to computational genomics.
A major outstanding topic in Condensed Matter Physics concerns how crystals form and grow, and what determines their atomic structure. Many experiments use microspheres floating in water to model atomic processes--like atoms they will spontaneously crystallize into ordered 3D arrays, but unlike atoms, the process is visible under a simple microscope. The proposed research will develop new methods for sticking these spheres together into new types of crystal structures by using DNA molecules attached to their surfaces. When two spheres come together bearing complementary halves of the double helix, the molecules will zip up pulling the spheres together. Besides being of fundamental interest, these new alloy-like crystals will be technologically useful as templates for so-called photonic bandgap materials, which some researchers believe will lead to more efficient lasers as well as faster computers and telecommunication systems. In addition, this work will provide chemical engineering students outstanding opportunities to pursue basic materials research, as well as master techniques ranging from microscopy to computational genomics.