Repurposing the blueprint for life through colloidal crystal engineering with DNA Chad Mirkin Northwestern University, Department of Chemistry and International Institute for Nanotechnology, 2145 Sheridan Road, Evanston, IL USA 60208 Email: chadnano@northwestern.edu To develop functional materials with properties by design, new synthetic strategies are needed to independently tune material composition and structure. However, it is exceedingly difficult to control complex interactions between atomic and molecular species in such a manner. Nanoscale building blocks, in contrast, can be encoded with programmable interactions through the ligands attached to their surface in a manner independent of the nanoparticle structure and composition. In our research, we have repurposed DNA from the genetic “blueprint for life” as a powerful programmable tool to use as a structure-directing agent and a structural material for materials assembly. Nanoparticle building block “atoms” can be densely functionalized with a shell of DNA ligands and assembled into sophisticated colloidal crystal structures with symmetries and spacings dictated by the DNA “bonds.” The sequence and length tunability of nucleic acid bonds has allowed us to define a powerful set of design rules for the construction of colloidal crystals with more than 78 unique lattice symmetries, interparticle distances spanning 7 nm to over 1 µm, eight well-defined crystal habits, and several phases that have no known mineral equivalent. We have recently expanded the scope of building blocks to hollow nanoframes, which enable the assembly of open-channel lattices with controlled pore geometry and size ranging from 10-1000 nm. Notably, colloidal crystals engineered using this approach exhibit emergent properties distinct from the nanoparticle and DNA building blocks. We have also shown that the DNA bonding elements impart remarkable shape memory properties, with full recovery of crystallinity and habit after 90% compression and loss of crystallinity upon dehydration. Finally, this unique genetic approach to materials design affords functional nanoparticle architectures with properties such as shape memory, pore size, and optical properties including wavelength dependent reflection, second harmonic generation, and negative refractive index.
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