Chiral Nanostructures

The early observation of exceptionally high circular dichroism in chiral nanostructures [1] has led to the rapid development of this field, encompassing particles and assemblies from nanoscale metals, semiconductors, ceramics, and allotropes of carbons. The chiral nanoparticles [2] and nanoassemblies display all chiral geometries found in organic stereochemistry, biological chemistry, and structural biology, such as tetrahedrons, helices, twisted rods and propellers, but at larger scales [3]. It is the larger dimensions and the greater polarizability of inorganic nanomaterials than organic chiral compounds that result in the giant optical activity. The size, geometry, and composition of chiral nanostructures can be tuned to resonate with a wide range of photon energies from ultraviolet to terahertz. The high intensity and sharpness of circular dichroism peaks of chiral nanostructures facilitated their use in biosensing [4].
Recent studies have revealed additional unique aspects of chiral nanostructures. Their absolute three-dimensional geometry can be accurately established by electron microscopy [5]. Unlike chiral molecules that exist as binary enantiomers, nanostructures display chirality continuum [6]. Also, chiral nanoparticles are essential for understanding the complexity of biological matter[7] because nanoscale chirality enforces reproducible self-assembly patterns while enabling adaptability to environmental conditions. And chiral nanoparticles selectively interact with biological counterparts of similar scale. The strength and selectivity of their interactions can be varied by nanoparticle geometry, surface ligands, and chemical composition [8].
Future research directions in the field of chiral nanostructures include the utilization of their multiscale chirality for chiral catalysis. The giant optical activity can be harnessed for the detecting and emitting circularly polarized light for emerging information technologies, including those under extreme conditions [9] and 6G/7G telecommunications, as well as polarization-based perception systems, and real-time holography. These possibilities can be enabled by the intense circularly polarized black body radiation from chiral nanostructures.
References
[1] Chen W. et al.; Nanoparticle Superstructures Made by Polymerase Chain Reaction: Collective Interactions of Nanoparticles and a New Principle for Chiral Materials. Nano Lett., 2009, 9, 2153–2159;
[2] Kotov, N.A. Inorganic Nanoparticles as Protein Mimics, Science, 2010, 330(6001), 188–189;
[3] Yan W.; et al.; Self-Assembly of Chiral Nanoparticle Pyramids with Strong R/S Optical Activity. J. Am. Chem. Soc., 2012, 134 (36), 15114;
[4] Zhao Y. et al, Shell-Engineered Chiro-plasmonic Assemblies of Nanoparticles for Zeptomolar DNA Detection, Nano Lett., 2014, 14 (7) 3908–3913;
[5] S. Jiang, Chiral Ceramic Nanoparticles of Tungsten Oxide and Peptide Catalysis, J. Am. Chem. Soc., 2017, 139, 13701;
[6] P Kumar et al. Photonically Active Bowtie Nanoassemblies with Chirality Continuum, Nature, 2023, 615, 418.
[7] W. Jiang, et al, Emergence of Complexity in Hierarchically Organized Chiral Particles, Science, 2020, 368, 6491, 642-648;
[8] L. Xu, et al, Enantiomer-Dependent Immunological Response of Nanoparticles with Light-Induced Chirality, Nature, 2022, 601, 366–373; [9] J. Lu, et al, Nano-achiral complex composites for extreme polarization optics , Nature, 2024, May 29, 630, 860–865