Nicholas Kotov1
University of Michigan1
Nanoscale chirality is a rapidly emerging field in science and engineering. The early observation of strong circular dichroism for individual nanoparticles (NPs) and their assemblies have developed into a rapidly expanding research area on chiral inorganic nanostructures. They encompass a large family of mirror-asymmetric constructs from metals, semiconductors, ceramics, and nanocarbons with multiple chiral geometries with characteristic scales from Ångströms to microns. Versatility in, scales, dimensions and polarizability of the inorganic materials enables their multiscale engineering to attain a broad range of optical and chemical properties. These capabilities as chiral materials enabled their fast technological translation for biosensing and optoelectronics, which, in turn, opened new venues for scientific inquiry into the unifying role chirality at the interface of materials science, biology, chemistry, and physics.<br/>Some of the latest directions in this field is understanding the fascinating relationships between multiscale chirality and structural/functional complexity of biomimetic nanomaterials forming from the spontaneous hierarchical ordering of inorganic building blocks over multiple scales. Empirical observations of complex nanoassemblies are abundant, but physicochemical mechanisms leading to their geometrical complexity remain puzzling, especially for non-uniformly sized components. These mechanisms are discussed in this talk taking an example of hierarchically organized particles with twisted spikes and other morphologies from polydisperse Au-Cys nanoplatelets [1]. The complexity of these supraparticles is higher than biological counterparts or other complex particles as enumerated by graph theory (GT). Complexity Index (<i>CI</i>) and other GT parameters are applied to a variety of different nanoscale materials to assess their structural organization. As the result of this analysis, we determined that intricate organization Au-Cys supraparticles emerges from competing chirality-dependent assembly restrictions that render assembly pathways primarily dependent on nanoparticle symmetry rather than size. These findings open a pathway to a large family of colloids with complex architectures and unusual chiroptical and chemical properties. The design principles elaborated for nanoplatelets have been extended to engineering of other complex nanoassemblies. They include polarization-based drug discovery platforms for Alzheimer syndrome,[2] materials for chiral photonics,[3] biomimetic composites for energy and robotics , CO<sub>2</sub>-dispersable catalysis,[4] chiral antiviral vaccines[5] and pharmaceutical quality control [6].<br/>References<br/>[1] W. Jiang, Z.-B. et al, Emergence of Complexity in Hierarchically Organized Chiral Particles, <i>Science</i>, <b>2020</b>, 368, 6491, 642-648.<br/>[2] Jun Lu, et al, Enhanced optical asymmetry in supramolecular chiroplasmonic assemblies with long-range order, <i>Science</i>, <b>2021</b>, 371, 6536, 1368.<br/>[3] L. Ohnoutek, et al, Third Harmonic Mie Scattering From Semiconductor Nanohelices, <i>Nature Photonics</i>, <b>2022</b>, 16, 126–133.<br/>[4] L. Tang et al. Self-Assembly Mechanism of Complex Corrugated Particles" <i>JACS, </i><b>2021 </b>143, 47, 19655–19667.<br/>[5] L. Xu, et al, Enantiomer-Dependent Immunological Response to Chiral Nanoparticles<b>, </b><i>Nature,</i><b> 2022</b>, 601, 366–373.<br/>[6] Choi W. et al, Chiral Phonons in Microcrystals and Nanofibrils of Biomolecules, <i>Nature Photonics</i>, <b>2022</b> 16, 366–373.