Halide-assisted differential growth of chiral nanoparticles with threefold rotational symmetry

Three-Dimensional Electron Microscopy of Chiral Nanoparticles: From Imaging to Measuring

The increasing interest in plasmonic nanoparticles with intrinsic chirality, i.e., reduced symmetry and strong optical activity, calls for characterization beyond qualitative imaging. In this context, three-dimensional electron microscopy (3D EM), which provides images containing information on the particles' surface and may even retrieve the explicit 3D shapes, is seeing exciting developments and applications. In this Mini-Review, we focus on scanning electron microscopy (SEM), electron tomography, and secondary electron electron-beam-induced current (SEEBIC). We highlight the recent advances in these 3D EM techniques and the analysis of their data that relate to chiral metallic nanoparticles. The study of shape-property relationships, in particular by quantitatively analyzing geometric chirality and informing electromagnetic simulations, is covered. New ways in which 3D characterization is revealing the growth pathways of the nanoparticles are also presented. Finally, we provide an outlook on future opportunities for 3D EM to further guide the understanding and development of (chiral) nanoparticles.

Glutathione: a naturally occurring tripeptide for functional metal nanomaterials

Glutathione (GSH), a naturally occurring tripeptide, plays an important role as an intracellular antioxidant in the physiological microenvironment and participates in redox balance, detoxification, and cellular and disease regulation. The unique structural features of GSH, including the reductive thiol and multiple coordination sites (carboxyl and amino group), make it a significant molecule not only in the physiological context but also as a ligand in the development of functional metal nanomaterials. In this context, GSH's role as a protective ligand and reducing agent in surface etching and ligand exchange reactions has been explored at the molecular level, expanding the diversity of GSH-protected metal nanomaterials. With photoluminescence (PL) as one of its most intriguing properties, investigations into GSH's influence on PL properties emphasize its multifaceted coordination capabilities in surface coating, charge transfer from electron-rich functional groups, chirality arising from its unique structure, and available conjugation sites. Moreover, the biocompatibility of GSH, combined with the synergistic effect of metal components, renders GSH-protected nanomaterials an "Inseparable Duo" highly suited for applications in bio-sensing, bio-imaging via PL radiative decay and anti-cancer bio-therapies through photothermal therapy, photodynamic therapy, and radiotherapy. By exploring the multifaceted roles of GSH, this Perspective aims to highlight pathways including the encouragement of deeper synthetic exploration, innovative design at the bio-nano interface, and expanded nanobiomedical applications.

Synthesis of chiral gold helicoid nanoparticles using glutathione

Chiral plasmonic nanostructures are in high demand because of their unique optical properties, which are applicable to polarization control, chiral sensing and biomedical applications. An easy and scalable synthesis method for these nanostructures may facilitate their development further. We have reported the synthesis for 432-symmetric chiral plasmonic nanoparticles by using a seed-mediated colloidal method facilitated by a chiral amino acid and peptides. Among those, 432 helicoid III nanoparticles particularly exhibited well-defined chiral morphologies and exceptional chiroptic properties, evidenced by a Kuhn's dissymmetry factor (g-factor) of 0.2, making them valuable for various applications. Here, we detail the synthesis stages, including the synthesis of seed nanoparticles, the verification of each stage outcome and the calibration of synthesis conditions. We further illustrate the troubleshooting section and video-document the stages to facilitate the reliable reproduction of 432 helicoid III nanoparticles. The procedure requires 8 h to complete and can be carried out by users with expertise in chemistry or materials science.

Strong Chiro-Optical Activity of Plasmonic Metasurfaces with Inverted Pyramid Arrays

Chiral plasmonics has emerged as a powerful tool for manipulating light at the nanoscale with unprecedented control over light polarization. The advances in nanofabrication have led to the creation of nanostructures that support strong chiroptical responses. However, the complexity of the fabrication and the associated high costs remain major challenges in upscaling these architectures. Here, we report on the development of chiral plasmonic metasurfaces composed of inverted pyramid arrays with mismatched directions with respect to the lattice vectors of the array. These metasurfaces are fabricated using a combination of soft lithography and anisotropic etching, resulting in cost-effective and reproducible chiral nanostructures without the need for expensive equipment. The fabricated metasurfaces exhibit high differential transmittance values in the visible spectrum, which are among the highest reported for plasmonic films. Theoretical modeling corroborates the experimental results, demonstrating the significant influence of the mismatch angle on the chiral behavior. Complete polarimetric characterization reveals exceptional chiro-optical activity with circular birefringence exceeding 375°/μm and Kuhn's dissymmetry factors (g-factors) approaching unity.

Enantioselective synthesis of chiroplasmonic helicoidal nanoparticles by nanoconfinement in chiral dielectric shells

Helicoid metal nanoparticles with intrinsic chirality have unveiled tailorable properties and unlocked many chirality-related applications across various fields. Nevertheless, the existing strategies for enantioselective synthesis of helicoid metal nanoparticles have been predominantly limited to gold. Here, we demonstrate a robust and versatile strategy for the enantioselective synthesis of helicoid nanoparticles beyond gold, leveraging chiral nanoconfinement provided by chiral SiO2 or nanoshells. The chiral nanoconfinement strategy enables the decoupling of ligand-directed crystal growth from chiral induction, allowing for the independent tuning of these two critical aspects. As a result, this approach can not only facilitate the replication of chiral shapes from the chiral nanoshells but also allow the generation of alternative chiral shapes. By employing this approach, we demonstrate the enantioselective synthesis of helicoid Pt, Au@Pt, Au@Pd, Au@Ag, and Au@Cu nanoparticles. The chiroplasmonic properties of Pt- and Pd-based chiral nanoparticles have been discovered, and the inversion of chiroplasmonic properties of Ag-based chiral nanoparticles via facet control has been documented and theoretically explained. The chiral nanoconfinement strategy enriches the toolbox for creating chiral nanoparticles and supports their exploration in diverse applications.

Chiral Gold Nanostructure Monolayers as SERS Substrates for Ultrasensitive Detection of Enantiomer Biomarkers of Alzheimer's Disease

The early diagnosis of neurodegenerative diseases, such as Alzheimer's disease (AD), requires the identification of sensitive and specific biomarkers. Detecting chiral molecules at concentrations relevant to disease states remains challenging. Herein, a new type of chiral gold nanostructure induced by D-/L-cysteine-leucine dipeptides with a g-factor of 0.1 was successfully synthesized for enantiomer biomarker detection. To enhance the discrimination performance, the chiral gold nanostructures were assembled into D-/L-Au monolayers. As surface-enhanced Raman scattering (SERS) substrates, the D-/L-Au monolayers simultaneously deliver molecular structural specificity and enantioselectivity within a single spectrum, which can be a versatile, label-free chiral discrimination strategy for the detection of D-/L-kynurenine (Kyn). The mechanism was unveiled to involve high enantioselective adsorption energies between L- and D-Kyn on the lattice plane (221), resulting in enantioselective sensing. The results showed that the L-Au monolayer reached a limit of detection (LOD) of 3.7 nm for L-Kyn, while the D-Au monolayer reached an LOD of 3.6 nM for D-Kyn. Notably, there was a significant difference in D-Kyn levels between AD patients and healthy individuals in serum samples, a distinction not observed for L-Kyn, which positioned D-Kyn as a potential novel biomarker for clinical prediagnosis of AD patients, marking the first report of its kind worldwide. This study provides a robust tool for advancing biomedical science and clinical diagnostics.

Circularly polarized OLEDs from chiral plasmonic nanoparticle-molecule hybrids

Organic light-emitting diodes (OLEDs) supporting the direct emission of circularly polarized (CP) light are essential for numerous technologies. The realization of CP-OLEDs with large dissymmetry (gEL) factors and high external quantum efficiencies (EQEs) has been accepted as a considerable challenge. Here we demonstrate the realization of efficient CP-OLEDs based on the assembly of chiral plasmonic nanoparticles (NPs) and supramolecular aggregates. The chiral plasmonic NPs serve as the chiral scaffold and chiral optical nanoantenna to modulate the circularly polarized absorption and emission of the supramolecular chromophores. We employ different chiral plasmonic NPs to construct various CP-OLEDs with the emission dominated by chiral excitons or chiral plasmons. The CP-OLED showing a high EQE of 2.5% and a large gEL factor of 0.31 is achieved, as a result of multiscale chirality transfer, plasmonic enhancement, and the suppression of the overshoot effect. The proposed schemes are compatible with the current manufacturing technology of OLEDs. This work demonstrates that chiral plasmonic NPs can be promising candidates in chiral photoelectric devices.

Recent Advances in Chiral Gold Nanomaterials: From Synthesis to Applications

In recent years, the field of chiral gold nanomaterials has witnessed significant advancements driven by their unique properties and diverse applications in various scientific domains. This review provides an in-depth examination of the synthesis methodologies and evolving applications of chiral gold nanomaterials, which have emerged as vital tools in areas such as antibacterial therapies, biosensing, catalysis, and nanomedicine. We start by discussing various synthesis techniques, focused on seed-mediated growth and circularly polarized light-assisted methods, each contributing to the controlled synthesis of chiral gold nanostructures with tailored optical activities. This review further delves into the applications of these nanomaterials, showcasing their potential in combating antibiotic-resistant bacteria, improving cancer immunotherapy, promoting tissue regeneration, and enabling precise biosensing through enhanced sensitivity and selectivity. We highlight the fundamental principles of chirality and its critical role in biological systems, emphasizing the importance of chiral gold nanomaterials in enhancing optical signals and facilitating molecular interactions. By consolidating recent findings and methodologies, this review endeavors to illuminate the promising future of chiral gold nanomaterials and their critical role in addressing contemporary scientific challenges.

Intrinsic Chirality Modulation and Biosensing Application of Helical Gold Nanorods by Anisotropic Etching

The investigation of plasmonic chirality is a profound and intriguing topic, and the distinctive morphology of intrinsically chiral nanoparticles has prompted significant interest in the structure-activity relationship between particle morphology and chirality. In this work, the anisotropic etching of chiral helical gold nanorods (HGNRs) by a cetyltrimethylammonium bromide (CTAB)-HAuCl4 complex was observed with an interesting bidirectional variation of intrinsic chirality that initially enhanced and subsequently weakened, which was related with the diversity in CTAB distribution. In addition, an ultrasensitive and convenient sensing platform for acetylcholinesterase was developed based on the circular dichroism signal recovery of HGNRs caused by the dual inhibition of HGNR etching. The distinctive etching process and mechanism of chiral nanoparticles offer new insights into understanding the structural features and biochemical applications of the plasmonic intrinsic chirality, which could be applied to the acquisition of chiral nanoparticles and sensitive detection platform based on chiral signal changes.

Enhanced Structure Stability of Au Nanobipyramids by an In Situ Customized Silver Armor

Revealing the structure stability and evolution of gold nanocrystals at the atomic scale is crucial to their versatile applications; however, the fundamental mechanism remains elusive due to the lack of in situ characterizations. In this work, the structural evolution of two types of Au nanobipyramids (Au NBPs) at elevated temperatures is monitored through in situ electron microscopy analysis, and there is a sharp distinction between their structure stability despite that they possess the same crystalline structure. Detailed material characterization reveals that the surface alloying of residual Ag with Au (customized Ag armor) can greatly inhibit the Au atom diffusion and contribute remarkably to the stability and surface-enhanced Raman scattering improvement. Moreover, the structure of the Au NBPs is further enhanced when the vulnerable tips are selectively coated with an oxide shell (Cu2O) to form a dumbbell-shaped nanostructure, which would undergo a completely different structure evolution at elevated temperatures.

Chiral Engineered Biomaterials: New Frontiers in Cellular Fate Regulation for Regenerative Medicine

Chirality, the property of objects that are nonsuperimposable on their mirror images, plays a crucial role in biological processes and cellular behaviors. Chiral engineered biomaterials have emerged as a promising approach to regulating cellular fate in regenerative medicine. However, few reviews provide a comprehensive examination of recent advancements in chiral biomaterials and their applications in cellular fate regulation. Herein, various fabrication techniques available for chiral biomaterials, including the use of chiral molecules, surface patterning, and self‐assembly are discussed. The mechanisms through which chiral biomaterials influence cellular responses, such as modulation of adhesion receptors, intracellular signaling, and gene expression, are explored. Notably, chiral biomaterials have demonstrated their ability to guide stem cell differentiation and augment tissue‐specific functions. The potential applications of chiral biomaterials in musculoskeletal disorders, neurodegenerative diseases, cardiovascular diseases, and wound healing are highlighted. Challenges and future perspectives, including standardization of fabrication methods and translation to clinical settings, are addressed. In conclusion, chiral engineered biomaterials offer exciting prospects for precisely controlling cellular fate, advancing regenerative medicine, and enabling personalized therapeutic strategies.

Chiral Inorganic Nanomaterials Characterized by Advanced TEM: A Qualitative and Quantitative Study

Chiral inorganic nanomaterials (CINMs) have garnered significant interest due to their exceptional optical, electronic, and catalytic properties, offering promising advancements in energy conversion, data storage, catalysis, and biomedicine. While traditional optical spectrophotometers reveal the chiroptical performance of CINMs on an ensemble level, the direct structural visualization for the qualitative and quantitative discernment of their chiral features has become increasingly distinct with the advancements of transmission electron microscopy (TEM) techniques. The need for reasonable and high-standard discrimination requirements of CINMs has driven the progress of chirality-based TEM technologies. Therefore, this review in the good season takes the initiative to summarize the current advancements in TEM technologies for CINMs characterization, emphasizing a qualitative analysis of chiral atomic-level features, 0D, 1D, and 2D nanocrystals, and assembled nanomaterials. Then, the quantitative methods for determining chirality is also highlighted, such as 3D electron tomography, and further address the evolution of chiral structures monitored by the Ex-situ and In-situ TEM technologies. By providing a roadmap for the current challenges and proposing future advancements in TEM technologies for the qualitative, quantitative, and real-time analysis of CINMs, it can drive innovations in the field of chiral nanomaterials as well as the development of TEM technologies.

Synthesis of Chiral Ag, Pd, and Pt Helicoids inside Chiral Silica Mold

Chiral inorganic nanomaterials hold significant promise for various applications, including enantioselective catalysis, polarization-controlling optical devices, metamaterials, and enantioselective molecular sensors. In our previous work, we presented a method for synthesizing chiral Au 432 helicoid III (Au helicoids) from peptides and amino acids, where helical gaps are intricately arranged with 432 symmetry within single cubic nanoparticles. In this study, we have achieved the fabrication of chiral silica molds through Au etching subsequent to the silica coating of Au helicoids. We demonstrate that these molds serve as geometrically confined reactors capable of producing chiral Ag, Pd, and Pt 432 helicoid III (Ag, Pd, and Pt helicoids). The morphology of the synthesized Ag, Pd, and Pt helicoids closely resembles that of the Au helicoids, exhibiting a superior g-factor compared to other reported chiral structures of each material. Notably, the Ag and Pd helicoids are found to be single-crystalline, with high-index planes exposed within the gaps. We believe that this silica mold-based approach can be generalized to synthesize chiral nanomaterials of various metal and even oxide materials.

Seed-Mediated Growth and Advanced Characterization of Chiral Gold Nanorods

The controlled growth of gold nanostructures with complex shapes and reduced symmetry, exemplified by chiral gold nanorods and nanoparticles, is one of the most dynamic fields of nanochemistry. A timely summary of underlying concepts, including growth mechanisms and redefined chirality measures, would further promote this research area. In this perspective, we aim to establish qualitative connections between the chiral shapes and growth conditions, specifically for the seed-mediated synthesis of chiral gold nanorods as a convenient case of chiral morphogenesis. The crystallographic and morphological features of achiral nanorods used as seeds, the experimental conditions during chiral growth, and the symmetry of the chiral inducers, can all be exploited to obtain nanorods with intricate chiral shapes. Chirality characterization (such as electron tomography techniques) and quantification (including chirality measures) emerge as critical aspects to comprehensively explore and understand such structures, enabling optimization of their geometric and optical features. We conclude by discussing relevant challenges to be addressed toward a better controlled synthesis of chiral plasmonic nanostructures.

Chiral plasmonic-dielectric coupling enables strong near-infrared chiroptical responses from helicoidal core-shell nanoparticles

Helicoid plasmonic nanoparticles with intrinsic chirality are an emerging class of artificial chiral materials with tailorable properties. The ability to extend their chiroplasmonic responses to the near-infrared (NIR) range is critically important for biomedical and nanophotonic applications, yet the rational design of such materials remains challenging. Herein, a strategy employing chiral plasmon-dielectric coupling is proposed to manipulate the chiroptical responses into the NIR region with high optical anisotropy. Through this strategy, the helicoid Au@Cu2O nanoparticles with structural chirality are designed and synthesized with tunable and enriched NIR chiroptical responses. Specially, a high optical anisotropy (g-factor) with a value of 0.35 is achieved in the NIR region, and multi-band chiroptical behaviors are observed. Spectral and electromagnetic simulations elucidate that strong coupling between chiroplasmonic core and chiral dielectric shell with high refractive index contributes to the rich and strong chiroptical responses, which are related to the interplay between various emerged and enhanced electric and magnetic multipolar resonance modes proved by multipole expansion analysis. Moreover, the helicoid Au@Cu2O nanoparticles display greater polarization rotation capability than the helicoid Au nanoparticles. This work offers mechanistic insights into chiral plasmon-dielectric coupling and suggests a general approach of creating NIR chiroplasmonic materials.

Unraveling the Origin of Reverse Plasmonic Circular Dichroism from Discrete Bichiral Au Nanoparticles

Bichiral plasmonic nanoparticles exhibited intriguing geometry-dependent circular dichroism (CD) reversal; however, the crucial factor that dominates the plasmonic CD is still unclear. Combined with CD spectroscopy and theoretical multipole analysis, we demonstrate that plasmonic CD originates from the excitation of electric quadrupolar plasmons. Moreover, a comparative study of two distinct quadrupolar modes reveals the correlation between the sign of the CD and the local geometric handedness at the plasmonic hotspots, thereby establishing a structure-property relationship in bichiral nanoparticles. The reverse CD is attributed to the opposite directions of the wavelength shift of the two plasmon modes upon changing the particle geometry. By finely tuning the size of bichiral nanoparticles, we can further reveal that the dependence of plasmonic CD on the electric quadrupolar plasmons. Our work sheds light on the physical origin of plasmonic CD and provides important guidelines for the design of chiral plasmonic nanoparticles toward chirality-dependent applications.

The promise of chiral electrocatalysis for efficient and sustainable energy conversion and storage: a comprehensive review of the CISS effect and future directions

The integration of chirality, specifically through the chirality-induced spin selectivity (CISS) effect, into electrocatalytic processes represents a pioneering approach for enhancing the efficiency of energy conversion and storage systems. This review delves into the burgeoning field of chiral electrocatalysis, elucidating the fundamental principles, historical development, theoretical underpinnings, and practical applications of the CISS effect across a spectrum of electrocatalytic reactions, including the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER). We explore the methodological advancements in inducing the CISS effect through structural and surface engineering and discuss various techniques for its measurement, from magnetic conductive atomic force microscopy (mc-AFM) to hydrogen peroxide titration. Furthermore, this review highlights the transformative potential of the CISS effect in addressing the key challenges of the NRR and CO2RR processes and in mitigating singlet oxygen formation in metal-air batteries, thereby improving their performance and durability. Through this comprehensive overview, we aim to underscore the significant role of incorporating chirality and spin polarization in advancing electrocatalytic technologies for sustainable energy applications.

Enantioselective Surface-Enhanced Raman Scattering by Chiral Au Nanocrystals with Finely Modulated Chiral Fields and Internal Standards

The chiral discrimination of enantiomers is crucial for drug screening and agricultural production. Surface-enhanced Raman scattering (SERS) is proposed for discriminating enantiomers benefiting from chiral plasmonic materials. However, the mechanism of enantioselective SERS is unclear, and fluctuating SERS intensities may result in errors. Herein, this work demonstrates a reliable SERS substrate using chiral Au nanocrystals with finely modulated chiral fields and internal standards. Chiral electromagnetic fields are enhanced after modulation, which is conducive to increasing the difference in the enantiomeric SERS intensity, as evidenced by the experimental and simulation results. Furthermore, the SERS stability is improved by the corrective effect of the internal standards, and the relative standard deviation is significantly reduced. Using finely modulated chiral fields and internal standards, L- and D-phenylalanine exhibit a stable six times difference in SERS ratio. Theoretical simulations reveal that linearly polarized light can also excite the chiral fields of chiral Au nanocrystals, indicating non-chiral far-field light is converted into chiral near-field sources by chiral Au nanocrystals. Thus, the mechanism of enantioselective SERS can be elucidated by the scattering difference of chiral molecules in chiral near fields. This study will pave the way for the development of enantioselective SERS and related chiroptical technologies.

Chirality Determination of Nanocrystals by Electron Crystallography

Chirality is a common phenomenon in nature and plays an important role in the properties of matter. The rational synthesis of chiral compounds and exploration of their applications in various fields require an unambiguous determination of their handedness. However, in many cases, determinations of the chiral crystal structure and chiral morphology have been a challenging task due to the lack of proper characterization methods, especially for nanosized crystals. Therefore, it is crucial to develop novel and efficient characterization methods. Owing to the strong interactions between matter and electrons, electron crystallography has become a powerful tool for structural analysis of nanomaterials. In recent years, methods based on electron crystallography, such as high-resolution electron microscopy imaging and electron diffraction, have been developed to unravel the chirality of nanomaterials. This brings new opportunities to the design, synthesis, and applications of versatile chiral nanomaterials. In this perspective, we summarize the recent methodology developments and ongoing research of electron crystallography for chiral structure and morphology determination of nanocrystals, including inorganic and organic materials, as well as highlight the potential and further improvement of these methods in the future.

Chiral Au-Pd Alloy Nanorods with Tunable Optical Chirality and Catalytically Active Surfaces

Integrating the plasmonic chirality with excellent catalytic activities in plasmonic hybrid nanostructures provides a promising strategy to realize the chiral nanocatalysis toward many chemical reactions. However, the controllable synthesis of catalytically active chiral plasmonic nanoparticles with tailored geometries and compositions remains a significant challenge. Here it is demonstrated that chiral Au-Pd alloy nanorods with tunable optical chirality and catalytically active surfaces can be achieved by a seed-mediated coreduction growth method. Through manipulating the chiral inducers, Au nanorods selectively transform into two different intrinsically chiral Au-Pd alloy nanorods with distinct geometric chirality and tunable optical chirality. By further adjusting several key synthetic parameters, the optical chirality, composition, and geometry of the chiral Au-Pd nanorods are fine-tailored. More importantly, the chiral Au-Pd alloy nanorods exhibit appealing chiral catalytic activities as well as polarization-dependent plasmon-enhanced nanozyme catalytic activity, which has great potential for chiral nanocatalysis and plasmon-induced chiral photochemistry.

Circular Differential Photocurrent Mapping of Hot Electron Response from Individual Plasmonic Nanohelicoids

Chiral plasmonic nanocrystals have recently attracted increasing attention in circular polarization-dependent photocatalysis driven by hot carriers. While being concealed in traditional ensemble measurements, the individual chiral photocatalytic activity of nanocrystals can exclusively be revealed by directly correlating the circular differential photocurrent response to helical morphologies using single-particle techniques. Herein, we develop a method named circular differential photocurrent mapping (CDPM) and demonstrate that CDPM can be used to characterize the circular differential hot electron (CDHE) response from individual Au nanohelicoids (AuNHs) on a TiO2 photoanode in a photoelectrochemical cell. The single-particle circular differential scattering and CDHE measurements were interpreted with calculations performed on a model in direct correlation to the helical morphologies of the nanocrystal. While CDHE response was found inactive at a dipolar resonance of 750 nm, helicity-convoluted sites of HE generation were identified on the AuNH at a specific higher-order mode of 550 nm, resulting in a significant response of CDHE in association with the handedness of the AuNH. Details of circular differential contributions were further resolved by examining the efficiencies of individual AuNHs in terms of g-factors. Our study provides a powerful microscopic method at the single-particle level for the photocatalytic characterization of chiral nanocrystals, gaining fundamental insights into the photocatalysis of chirality, especially toward plasmon-induced asymmetrical photochemistry or photoelectrochemistry.

Cu2+-Dominated Chirality Transfer from Chiral Molecules to Concave Chiral Au Nanoparticles

Foreign ions as additives are of great significance for realizing excellent control over the morphology of noble metal nanostructures in the state-of-the-art seed-mediated growth method; however, they remain largely unexplored in chiral synthesis. Here, we report on a Cu2+-dominated chiral growth strategy that can direct the growth of concave chiral Au nanoparticles with C3-dominant chiral centers. The introduction of trace amounts of Cu2+ ions in the seed-mediated chiral growth process is found to dominate the chirality transfer from chiral molecules to chiral nanoparticles, leading to the formation of chiral nanoparticles with a concave VC geometry. Both experimental and theoretical results further demonstrate the correlation between the nanoparticle structure and optical chirality for the concave chiral nanoparticle. The Cu2+ ion is found to dominate the chiral growth by selectively activating the deposition of Au atoms along the [110] and [111] directions, facilitating the formation of the concave VC. We further demonstrate that the Cu2+-dominated chiral growth strategy can be employed to generate a variety of concave chiral nanoparticles with enriched geometric chirality and desired chiroptical properties. Concave chiral nanoparticles also exhibit appealing catalytic activity and selectivity toward electrocatalytic oxidation of enantiomers in comparison to helicoidal nanoparticles. The ability to tune the geometric chirality in a controlled manner by simply manipulating the Cu2+ ions as additives opens up a promising strategy for creating chiral nanomaterials with increasing architectural diversity for chirality-dependent optical and catalytic applications.

Tuning the Geometry and Optical Chirality of Pentatwinned Au Nanoparticles with 5-Fold Rotational Symmetry

Chirality transfer from chiral molecules to chiral nanomaterials represents an important topic for exploring the origin of chirality in many natural and artificial systems. Moreover, developing a promising class of chiral nanomaterials holds great significance for various applications, including sensing, photonics, catalysis, and biomedicine. Here we demonstrate the geometric control and tunable optical chirality of chiral pentatwinned Au nanoparticles with 5-fold rotational symmetry using the seed-mediated chiral growth method. A distinctive growth pathway and optical chirality are observed using pentatwinned decahedra as seeds, in comparison with the single-crystal Au seeds. By employing different peptides as chiral inducers, pentatwinned Au nanoparticles with two distinct geometric chirality (pentagonal nanostars and pentagonal prisms) are obtained. The intriguing formation and evolution of geometric chirality with the twinned structure are analyzed from a crystallographic perspective upon maneuvering the interplay of chiral molecules, surfactants, and reducing agents. Moreover, the interesting effects of the molecular structure of peptides on tuning the geometric chirality of pentatwinned Au nanoparticles are also explored. Finally, we theoretically and experimentally investigate the far-field and near-field optical properties of chiral pentatwinned Au nanoparticles through numerical simulations and single-particle chiroptical measurements. The ability to tune the geometric chirality in a controlled manner represents an important step toward the development of chiral nanomaterials with increasing architectural complexity for chiroptical applications.

Nanophotonic Enhanced Chiral Sensing and Its Biomedical Applications

Chiral sensing is crucial in the fields of biology and the pharmaceutical industry. Many naturally occurring biomolecules, i.e., amino acids, sugars, and nucleotides, are inherently chiral. Their enantiomers are strongly associated with the pharmacological effects of chiral drugs. Owing to the extremely weak chiral light-matter interactions, chiral sensing at an optical frequency is challenging, especially when trace amounts of molecules are involved. The nanophotonic platform allows for a stronger interaction between the chiral molecules and light to enhance chiral sensing. Here, we review the recent progress in nanophotonic-enhanced chiral sensing, with a focus on the superchiral near-field and enhanced circular dichroism (CD) spectroscopy generated in both the dielectric and in plasmonic structures. In addition, the recent applications of chiral sensing in biomedical fields are discussed, including the detection and treatment of difficult diseases, i.e., Alzheimer's disease, diabetes, and cancer.

Homochiral Nanopropeller via Chiral Active Surface Growth

Under the control of chiral ligand glutathione and in the presence of hexadecyltrimethylammonium bromide, Au deposition on Au seeds is known to give chiral nanostructures. We have previously shown that the protruding chiral patterns, as opposed to flat facets, are likely caused by active surface growth, where nonuniform ligand coverage could be responsible for the focused growth at a few active sites. By pushing the limit of such a growth mode, here, we use decahedral seeds to prepare homochiral nanopropellers with intricate patterns of deep valleys and protruding ridges. Control experiments show that the focused growth depends on the rates of Au deposition by changing either the seed concentration or the reductant concentration, consistent with the proposed mechanism. The dynamic growth competition between the ligand-deficient active sites and the ligand-rich surfaces gradually focuses the growth onto a few active sites, causing the expansion of grooves, squeezing of steep ridges, and a surprising 36° rotation of the pentagonal outline. The imbalanced deposition on the prochiral slopes is responsible for the tilted grooves, the twisted walls, and thus the well-separated and distorted blades, which become the origin of the chiroptical responses.

Chiral Plasmonic Hybrid Nanostructures: A Gateway to Advanced Chiroptical Materials

Chirality introduces a new dimension of functionality to materials, unlocking new possibilities across various fields. When integrated with plasmonic hybrid nanostructures, this attribute synergizes with plasmonic and other functionalities, resulting in unprecedented chiroptical materials that push the boundaries of the system's capabilities. Recent advancements have illuminated the remarkable chiral light-matter interactions within chiral plasmonic hybrid nanomaterials, allowing for the harnessing of their tunable optical activity and hybrid components. These advancements have led to applications in areas such as chiral sensing, catalysis, and spin optics. Despite these promising developments, there remains a need for a comprehensive synthesis of the current state-of-the-art knowledge, as well as a thorough understanding of the construction techniques and practical applications in this field. This review begins with an exploration of the origins of plasmonic chirality and an overview of the latest advancements in the synthesis of chiral plasmonic hybrid nanostructures. Furthermore, representative emerging categories of hybrid nanomaterials are classified and summarized, elucidating their versatile applications. Finally, the review engages with the fundamental challenges associated with chiral plasmonic hybrid nanostructures and offer insights into the future prospects of this advanced field.

Mercury-Mediated Epitaxial Accumulation of Au Atoms for Stained Hydrogel-Improved On-Site Mercury Monitoring

Trivalent Au ions are easily reduced to be zerovalent atoms by coexisting reductant reagents, resulting in the subsequent accumulation of Au atoms and formation of plasmonic nanostructures. In the absence of stabilizers or presence of weak stabilizers, aggregative growth of Au nanoparticles (NPs) always occurs, and unregular multidimensional Au materials are consequently constructed. Herein, the addition of nanomole-level mercury ions can efficiently prevent the epitaxial accumulation of Au atoms, and separated Au NPs with mediated morphologies and superior plasmonic characteristics are obtained. Experimental results and theoretical simulation demonstrate the Hg-concentration-reliant formation of plasmonic nanostructures with their mediated sizes and shapes in the presence of weak reductants. Moreover, the sensitive plasmonic responses of reaction systems exhibit selectivity comparable to that of Hg species. As a concept of proof, polymeric carbon dots (CDs) were used as the initial reductant, and the reactions between trivalent Au and CDs were studies. Significantly, Hg atoms prevent the epitaxial accumulation of Au atoms, and plasmonic NPs with decreased sizes were in situ synthesized, corresponding to varied surface plasmonic resonance absorption performance of the CD-induced hybrids. Moreover, with the integration of sensing substrates of CD-doped hydrogels, superior response stabilities, analysis selectivity, and sensitivity of Hg2+ ions were achieved on the basis of the mercury-mediated in situ chemical reactions between trivalent Au ions and reductant CDs. Consequently, a high-performance sensing strategy with the use of Au NP-staining hydrogels (nanostaining hydrogels) was exhibited. In addition to Hg sensing, the nanostaining hydrogels facilitated by doping of emerging materials and advanced chem/biostrategies can be developed as high-performance on-site monitoring routes to various pollutant species.

Tuning the Plexcitonic Optical Chirality Using Discrete Structurally Chiral Plasmonic Nanoparticles

Constructing chiral plexcitonic systems with tunable plasmon-exciton coupling may advance the scientific exploitation of strong light-matter interactions. Because of their intriguing chiroptical properties, chiral plasmonic materials have shown promising applications in photonics, sensing, and biomedicine. However, the strong coupling of chiral plasmonic nanoparticles with excitons remains largely unexplored. Here we demonstrate the construction of a chiral plasmon-exciton system using chiral AuAg nanorods and J aggregates for tuning the plexcitonic optical chirality. Circular dichroism spectroscopy was employed to characterize chiral plasmon-exciton coupling, in which Rabi splitting and anticrossing behaviors were observed, whereas the extinction spectra exhibited less prominent phenomena. By controlling the number of molecular excitons and the energy detuning between plasmons and excitons, we have been able to fine-tune the plexcitonic optical chirality. The ability to fine-tune the plexcitonic optical chirality opens up unique opportunities for exploring chiral light-matter interactions and boosting the development of emerging chiroptical devices.

Geometric Control and Optical Properties of Intrinsically Chiral Plasmonic Nanomaterials

Intrinsically chiral plasmonic nanomaterials exhibit intriguing geometry-dependent chiroptical properties, which is due to the combination of plasmonic features with geometric chirality. Thus, chiral plasmonic nanomaterials have become promising candidates for applications in biosensing, asymmetric catalysis, biomedicine, photonics, etc. Recent advances in geometric control and optical tuning of intrinsically chiral plasmonic nanomaterials have further opened up a unique opportunity for their widespread applications in many emerging technological areas. Here, the recent developments in the geometric control of chiral plasmonic nanomaterials are reviewed with special attention given to the quantitative understanding of the chiroptical structure-property relationship. Several important optical spectroscopic tools for characterizing the optical chirality of plasmonic nanomaterials at both ensemble and single-particle levels are also discussed. Three emerging applications of chiral plasmonic nanomaterials, including enantioselective sensing, enantioselective catalysis, and biomedicine, are further highlighted. It is envisioned that these advanced studies in chiral plasmonic nanomaterials will pave the way toward the rational design of chiral nanomaterials with desired optical properties for diverse emerging technological applications.