Biomimetic Hierarchical Assembly of Helical Supraparticles from Chiral Nanoparticles

Chiroptical materials found in butterflies, beetles, stomatopod crustaceans, and other creatures are attributed to biocomposites with helical motifs and multiscale hierarchical organization. These structurally sophisticated materials self-assemble from primitive nanoscale building blocks, a process that is simpler and more energy efficient than many top-down methods currently used to produce similarly sized three-dimensional materials. Here, we report that molecular-scale chirality of a CdTe nanoparticle surface can be translated to nanoscale helical assemblies, leading to chiroptical activity in the visible electromagnetic range. Chiral CdTe nanoparticles coated with cysteine self organize around Te cores to produce helical supraparticles. D-/L-Form of the amino acid determines the dominant left/right helicity of the supraparticles. Coarse-grained molecular dynamics simulations with a helical pair-potential confirm the assembly mechanism and the origin of its enantioselectivity, providing a framework for engineering three-dimensional chiral materials by self-assembly. The helical supraparticles further self-organize into lamellar crystals with liquid crystalline order, demonstrating the possibility of hierarchical organization and with multiple structural motifs and length scales determined by molecular-scale asymmetry of nanoparticle interactions.This material is based upon work supported by the U.S. Army Research Office under Grant Award No. ARO MURI W911NF-10-1-0518. Y.L.Z. acknowledges support from National Natural Science Foundation of China (NSFC-21573162) and WIBEZD2014001-02. R.L.M. and N.A.K. were supported in part by the National Science Foundation, Division of Materials Research Award # DMR 1120923. N.A.K also wishes to acknowledge support from NSF under grants ECS-0601345; CBET 0933384; CBET 0932823; and CBET 1036672. We thank the University of Michigan's Electron Microscopy and Analysis Laboratory (EMAL) for its assistance with electron microscopy and for NSF grants (numbers DMR-0320740 and DMR-9871177), for funding the FEI Nova Nanolab Dualbeam focused ion beam workstation and scanning electron microscope and the JEM-2010F analytical electron microscope used in this work. Y.L.Z. thanks Jinyan Chen and Hailin Qiu for the assistance with the PL lifetime experiment. R.L.M. is grateful to Matthew Spellings for numerous fruitful discussions. Simulations were carried out using computational resources and services supported by Advanced Research Computing at the University of Michigan, Ann Arbor. The experiments performed at the Molecular Foundry, Lawrence Berkeley National Laboratory were supported by the U.S. Department of Energy under contract no. DE-AC02-05CH11231. We also thank EMAL and the College of Engineering for assistance with the Bruker NanoStar small-angle X-ray scattering. The experiments performed at the Molecular Foundry, Lawrence Berkeley National Laboratory were supported by the U.S. Department of Energy under contract #DE-AC02-05CH11231