Extension of Compositional Space to the Ternary in Alloy Chiral Nanoparticles through Galvanic Replacement Reactions

Chiral nanomaterial-based approaches for diagnosis and treatment of protein-aggregated neurodiseases: current status and future opportunities

Protein misfolding and its aggregation, known as amyloid aggregates (Aβ), are some of the major causes of more than 20 diseases such as Parkinson's disease, Alzheimer's disease, and type 2 diabetes. The process of Aβ formation involves an energy-driven oligomerization of Aβ monomers, leading to polymerization and eventual aggregation into fibrils. Aβ fibrils exhibit multilevel chirality arising from its amino acid residues and the arrangement of folded polypeptide chains; thus, a chirality-driven approach can be utilized for the detection and inhibition of Aβ fibrils. In this regard, chiral nanomaterials have recently opened new possibilities for various biomedical applications owing to their stereoselective interaction with biological systems. Leveraging this chirality-driven approach with chiral nanomaterials against protein-aggregated diseases could yield promising results, particularly in the early detection of Aβ forms and the inhibition of Aβ aggregate formation via specific and strong "chiral-chiral interaction." Despite the advantages, the development of advanced theranostic systems using chiral nanomaterials against protein-aggregated diseases has received limited attention so far because of considerably limited formulations for chiral nanomaterials and lack of information of their chiroptical behavior. This review aims to present the current status of chiral nanomaterials explored for detecting and inhibiting Aβ forms. This review covers the origin of chirality in amyloid fibrils and nanomaterials and different chiral detection methods; furthermore, different chiral nanosystems such as chiral plasmonic nanomaterials, chiral carbon-based nanomaterials, and chiral nanosurfaces, which have been used so far for different therapeutic applications against protein-aggregated diseases, are discussed in detail. The findings from this review may pave the way for the development of novel approaches using chiral nanomaterials to combat diseases resulting from protein misfolding and can further be extended to other disease forms.

Multicomponent chiral plasmonic hybrid nanomaterials: recent advances in synthesis and applications

Chiral hybrid nanomaterials with multiple components provide a highly promising approach for the integration of desired chirality with other functionalities into one single nanoscale entity. However, precise control over multicomponent chiral plasmonic hybrid nanomaterials to enable their application in diverse and complex scenarios remains a significant challenge. In this review, our focus lies on the recent advances in the preparation and application of multicomponent chiral plasmonic hybrid nanomaterials, with an emphasis on synthetic strategies and emerging applications. We first systematically elucidate preparation methods for multicomponent chiral plasmonic hybrid nanomaterials encompassing the following approaches: physical deposition approach, galvanic replacement reaction, chiral molecule-mediated, chiral heterostructure, circularly polarized light-mediated, magnetically induced, and chiral assembly. Furthermore, we highlight emerging applications of multicomponent chiral plasmonic hybrid nanomaterials in chirality sensing, enantioselective catalysis, and biomedicine. Finally, we provide an outlook on the challenges and opportunities in the field of multicomponent chiral plasmonic hybrid nanomaterials. In-depth investigations of these multicomponent chiral hybrid nanomaterials will pave the way for the rational design of chiral hybrid nanostructures with desirable functionalities for emerging technological applications.

Mesoporous alloy chiral nanoparticles with high production yield and strong optical activities

Applying galvanic replacement reactions (GRRs) to the host chiral nanoparticles (CNPs) is an exclusive method to generate alloy CNPs with mesoporous structures through chirality transfer. However, the GRR-mediated chirality transfer is too inefficient to impose strong optical activities on the alloy mesoporous CNPs (or m-CNPs). Here we dope the host with gold (Au) to significantly enhance the chirality transfer, and additionally employ the Au adhesion layer to increase the production yield (PY) of binary m-CNPs.

Nanohelix-Induced Optical Activity of Liquid Metal Nanoparticles

Liquid metals (such as gallium or Ga) exist in liquid states under ambient conditions and are hardly sculpted in chiral structures. Herein, through electron-beam evaporation of Ga, hemispherical achiral Ga nanoparticles (NPs) are randomly immobilized along helical surfaces of SiO₂ nanohelices (NHs), functioning as a chiral template. Helical assembly of Ga NPs shows chiroplasmonic optical activity owing to collective plasmon-plasmon interactions, which can be tuned as a function of a helical SiO₂ pitch (P) and the amount of Ga evaporated. At a P of ≈150 nm, the chiroplasmonic optical activity, evaluated with anisotropic g-factor, can be as large as ≈0.1. Because the SiO₂ NHs and Ga NPs have high environmental stability of nanostructures, the chiroplasmonic optical activity shows excellent anti-aging stability, despite slight blue shift and chiroplasmonic degradation for the first 2 weeks. Spontaneous oxidation of the Ga NPs enables the formation of dense Ga₂ O₃ layers covering Ga cores to prevent further oxidation and thus to stabilize the chiroplasmonic optical activity. This work devises an alternative approach to impose optical activity onto Ga NPs, providing an additional degree of freedom (i.e., chirality) for Ga-based flexible electronic devices to develop advanced applications of 3D display, circular polarizers, bio-imaging, and bio-detection.

Chiral Nanoparticles with Enhanced Thermal Stability of Chiral Structures through Alloying

Metallic chiral nanoparticles (CNPs) promisingly function as asymmetric catalysts but lack an important study in thermal stability of optical activity that stems from metastable chiral lattices. In this work, annealing is applied to silver (Ag) CNPs, fabricated by glancing angle deposition (GLAD), and causes elimination of optical activity at 200 °C, mainly ascribed to chiral-to-achiral lattice transformation. The Ag CNPs are remarkedly enhanced in thermal stability through an alloying with aluminum (Al) via layer-by-layer GLAD to generate binary Ag_0.5 Al_0.5 CNPs composed of solid-state liquids, whose optical activity vanishes at 700 °C. Ease in the diffusion of Al atoms in the host Ag CNPs and thermal insulation from the Al₂ O₃ layers partially covering the binary CNPs effectively prohibit structural relaxation of the metastable chiral lattices, accounting for the significant enhancement in thermal stability of chiral lattices. This is a pioneering work to investigate the fundamental principles determining the thermal stability of metallic CNPs in terms of chiral structures and optical activity. It paves the way toward applying metallic CNPs to asymmetric catalysis at high temperature to accelerate an asymmetric synthesis of enantiomers with designable chirality, which is one of the most important topics in modern chemistry.

Recent Advances in Inorganic Chiral Nanomaterials

Inorganic nanoparticles offer a multifunctional platform for biomedical applications in drug delivery, biosensing, bioimaging, disease diagnosis, screening, and therapies. Homochirality prevalently exists in biological systems composed of asymmetric biochemical activities and processes, so biomedical applications essentially favor the usage of inorganic chiral nanomaterials, which have been widely studied in the past two decades. Here, the latest investigations are summarized including the characterization of 3D stereochirality, the bionic fabrication of hierarchical chirality, extension of the compositional space to poly-elements, studying optical activities with the (sub-)single-particle resolution, and the experimental demonstration in biomedical applications. These advanced studies pave the way toward fully understanding the two important chiral effects (i.e., the chiroptical and enantioselective effects), and prospectively promote the flexible design and fabrication of inorganic chiral nanoparticles with engineerable functionalities to solve diverse practical problems closely associated with environment and public health.

Broad Chiroptical Activity from Ultraviolet to Short-Wave Infrared by Chirality Transfer from Molecular to Micrometer Scale

Chiral nanomaterials provide a rich platform for versatile applications. Tuning the wavelength of polarization rotation maxima in the broad range including short-wave infrared (SWIR) is a promising candidate for infrared neural stimulation, imaging, and nanothermometry. However, the majority of previously developed chiral nanomaterials reveal the optical activity in a relatively shorter wavelength range (ultraviolet-visible, UV-vis), not in SWIR. Here, we demonstrate a versatile method to synthesize chiral copper sulfides using cysteine, as the stabilizer, and transferring the chirality from molecular- to the microscale through self-assembly. The assembled structures show broad chiroptical activity in the UV-vis-NIR-SWIR region (200-2500 nm). Importantly, we can tune the chiroptical activity by simply changing the reaction conditions. This approach can be extended to materials platforms for developing next-generation optical devices, metamaterials, telecommunications, and asymmetric catalysts.

Shining light on chiral inorganic nanomaterials for biological issues

The rapid development of chiral inorganic nanostructures has greatly expanded from intrinsically chiral nanoparticles to more sophisticated assemblies made by organics, metals, semiconductors, and their hybrids. Among them, lots of studies concerning on hybrid complex of chiral molecules with achiral nanoparticles (NPs) and superstructures with chiral configurations were accordingly conducted due to the great advances such as highly enhanced biocompatibility with low cytotoxicity and enhanced penetration and retention capability, programmable surface functionality with engineerable building blocks, and more importantly tunable chirality in a controlled manner, leading to revolutionary designs of new biomaterials for synergistic cancer therapy, control of enantiomeric enzymatic reactions, integration of metabolism and pathology via bio-to nano or structural chirality. Herein, in this review our objective is to emphasize current research state and clinical applications of chiral nanomaterials in biological systems with special attentions to chiral metal- or semiconductor-based nanostructures in terms of the basic synthesis, related circular dichroism effects at optical frequencies, mechanisms of induced optical chirality and their performances in biomedical applications such as phototherapy, bio-imaging, neurodegenerative diseases, gene editing, cellular activity and sensing of biomarkers so as to provide insights into this fascinating field for peer researchers.

One-Fold Anisotropy of Silver Chiral Nanoparticles Studied by Second-Harmonic Generation

Second-harmonic generation (SHG) integrated with diverse nonlinear optical activity characterization has high sensitivity to detect the symmetry of materials at an interface, but the study is in its infancy. Here, we employ SHG with linear dichroism (or SHG-LD) to study the chiroptical origin of silver (Ag) chiral nanoparticles (CNPs) deposited by glancing angle deposition (GLAD). It is found that Ag CNPs show the chiroptical activity ascribed to not only the structural chirality (i.e., atomically chiral lattices) but also one-fold anisotropy at an interface due to the substrate rotation during GLAD. Therefore, the SHG-LD shows great potential to provide valuable complementary information to study the chiroptical properties of chiral metamaterials.