George Schatz1
Northwestern University1
This talk will present recent studies of the Schatz group in collaboration with the Stupp and Mirkin groups at Northwestern concerning the self-assembly of actuatable nanostructures using peptide and DNA components. In the case of the Mirkin collaboration, we are interested in using DNA as a linker to make superlattice crystals of gold nanoparticles. Previously this technology has been adapted to make superlattices of cubic nanoparticles, leading to a primitive cubic crystal habit that provides unusual optical properties in the infrared, when the DNA length is reduced by adding ethanol, due to Mie resonance excitation. A problem with this direction is that the resulting crystal habits are significantly defected, and the habit size is restricted by sedimentation. In new work, we have significantly improved on both of these problems by considering metasurface formation. A key discovery in this work is that superlattice defects can be greatly reduced by using self-complementary sticky ends on the DNA linkers in combination with careful temperature control during hybridization. The new superlattices are of higher quality over much larger areas, and with improved optical properties compared to past work.<br/>Our collaboration with Stupp concerns studies of peptide amphiphile self-assembly to produce cylindrical micelles and ribbons, and ultimately fiber materials that can be used for applications in biomedicine and for making materials that can be photoactivated for robotic functions. Experiments show that sometimes the self-assembly makes micelles and sometimes ribbons, but features of the peptide amphiphiles that determine ribbon structures and chirality have not been determined. Here we consider peptides based on valine-glutamic acid repeats, (VE)<sub>n</sub>, to reveal the underlying structure of the ribbon, and its chirality. Using all-atom molecular dynamics, we show that the observed left handed twist is correlated with the stacking of right handed beta-sheets that is perpendicular to the ribbon growth direction. We also show that adding GRGD peptide sequencies to the VE repeats greatly changes the ribbon structure, even reversing chirality in some cases. The use of cylindrical micelle structures to make actuatable materials will also be described.