Chiral Plasmonic Research Articles

Nanoparticle manipulation based on chiral plasmon effects.

Chiral plasmonic structures have garnered increasing attention owing to their distinctive chiroptical response. Localized surface plasmon resonance can significantly enhance the circular dichroism and local electromagnetic field of chiral plasmonic structures, resulting in enhanced electromagnetic forces acting on surrounding nanoparticles. Moreover, the circular dichroism response of chiral structures provides an effective means for macroscopic adjustment of microscopic electromagnetic fields. However, chiral plasmon effects are naturally related to angular momentum, and particle control studies of chirality usually focus on angular momentum. This paper proposes a particle manipulation method utilizing chiral light-matter interactions. Through optimization of the optical response of the chiral structure, the direction of electromagnetic forces exerted on surrounding polystyrene particles reverses upon a change in the incident light's handedness. According to this characteristic, the movement direction control of polystyrene particles with a diameter of 100 nm was achieved. By altering the handedness of a single circularly polarized light, more than 94% high-precision particle manipulation was achieved, reducing the complexity of particle manipulation. This microfluidic method has significant implications for advancing microfluidic research and chiral applications.

Engineering copper plasmonic chirality via ligand-induced dissolution for enantioselective recognition of amino acids.

The formation of chiral nanosystems and their subsequent enantioselective interaction with chiral amino acids are vital steps in many biological processes. Due to their potential to mimic biological systems, the synthesis of chiral nanomaterials has garnered significant attention over the years. Despite the emergence of diverse nanomaterials showcasing strong chiral responses, the in-depth understanding of the mechanism of plasmonic chirality in copper nanoparticles and their subsequent application in various fields are least explored. Herein, we demonstrate a facile approach for the synthesis of chiral copper nanoparticles using cysteine as a chiral precursor and capping ligand. Ligand-mediated chiral induction, established through experimental findings and a theoretical model, is ascribed as the major contributor to the origin of plasmonic chirality. The enantioselective recognition of chiral copper nanoparticles towards histidine, an amino acid with vast biological functions, was meticulously investigated by leveraging the strong copper-histidine binding ability. Ligand-induced dissolution, a unique phenomenon in nanoparticle reactions, was identified as the underlying mechanism for the nanoparticle-to-complex conversion. Understanding the mechanism of chiral induction in copper nanoparticles coupled with their enantioselective recognition of biomolecules not only holds promise in biomedical research but also sheds light on their potential as catalysts for asymmetric synthesis.

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.

Fabrication of Chiral Plasmonic Photocatalyst By Circularly Polarized Light and Enantioselective Hydrogen Generation Activity

Introducing chirality in nanostructures has been explored actively in various field, such as sensing, optoelectronics and catalysts, due to its unique chiroptical properties. Especially in photochemistry, considering the synergistic interaction between chiral plasmonics and polarized light, they can be utilized to improve efficiency and selectivity of catalytic reaction. In this work, we synthesized chiral plasmonic photocatalysts, (R)-,(L)- Au/C3N4, through photoreduction of gold precursor on C3N4 substrate under the irradiation of circularly polarized light (CPL) as a means to induce chirality. Then, we demonstrated that the efficiency of hydrogen generation can be increased by matching the chirality of the CPL with the photocatalyst, which was 2-fold enhanced than chiral mismatching conditions. This can be explained by the asymmetric hot carrier formation of chiral plasmonic structures under CPL excitation. Also, the reactivity of water molecule with photocatalyst surface was confirmed through in-situ FT-IR, showing the enhanced interaction under chiral matching conditions. This study could pave the way for advancing chiral light-matter interactions and explore the application of novel device, particularly toward chiral-induced photocatalytic performance.

Tuning Q-Factor and Perfect Absorption Using Coupled Tamm States on Polarization-Preserving Metasurface

The circular polarization of light flips its handedness after a conventional metallic mirror reflection. Therefore, a polarization-preserving metasurface is a crucially important element in a series of chiral photonic structures. They include tunable cholesteric LCs and anisotropic photonic crystals. Chiral structures are rich in interfacial localized modes including Tamm states. In this report, coupled modes formed as a result of the interaction between two chiral optical Tamm states or a chiral optical Tamm state and a chiral Tamm plasmon polariton are analytically and numerically investigated. It is shown that the effective control of coupled modes can be carried out by changing the pitch of the cholesteric and the angle between the optical axis of the cholesteric and the polarization-preserving anisotropic mirror. The influence of the metasurface period on the spectral characteristics of coupled modes is investigated. The possibility of realizing a bound state in the continuum of the Friedrich–Wintgen type, resulting from the destructive interference of coupled modes, which leads to the collapse of the resonance line corresponding to the chiral optical Tamm state, has been demonstrated.

Reversible Ultrafast Chiroptical Responses in Planar Plasmonic Nano-Oligomer.

Ultracompact chiral plasmonic nanostructures with unique chiral light-matter interactions are vital for future photonic technologies. However, previous studies are limited to reporting their steady-state performance, presenting a fundamental obstacle to the development of high-speed optical devices with polarization sensitivity. Here, a comprehensive analysis of ultrafast chiroptical response of chiral gold nano-oligomers using time-resolved polarimetric measurements is provided. Significant differences are observed in terms of the absorption intensity, thus hot electron generation, and hot carrier decay time upon polarized photopumping, which are explained by a phenomenological model of the helicity-resolved optical transitions. Moreover, the chiroptical signal is switchable by reversing the direction of the pump pulse, demonstrating the versatile modulation of polarization selection in a single device. The results offer fundamental insights into the helicity-resolved optical transitions in photoexcited chiral plasmonics and can facilitate the development of high-speed polarization-sensitive flat optics with potential applications in nanophotonics and quantum optics.

Planar oligomerization of reconfigurable gold nanorod dimers.

Reconfigurable chiral plasmonic complexes are fabricated by planar assembly of multiple individual gold nanorod dimers using DNA origami templates. Additionally, each chiral center can be controlled to switch among achiral, left-handed, and right-handed states. We demonstrate that their overall circular dichroism is determined by the coupling of individual chiral centers and is heavily influenced by the precise number and arrangement of these centers. Our study offers a novel self-assembly method for constructing intricate and dynamic chiral plasmonics as well as investigating the interactions among several plasmonic chiral centers.

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.

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.

Tunable Chiral Plasmonic Activities Enabled via Stimuli Responsive Micro-Origami.

Chiral plasmonic nanomaterials with distinctive circularly polarized light-dependent optical responses over a broad range of frequency have great potential for photonic and biomedical applications. However, it still remains challenging to fabricate 3D plasmonic chiral micro-constructs with readily modulated chiroptical properties over the magnitude of ellipticity, mode frequency, and switchable handedness, especially in the vis-NIR range. In this study, polymeric micro-origami-based 3D plasmonic chiral structures are constructed through self-rolling of gold nanospheres (AuNSs)-decorated polymeric micro-sheets. Spherical AuNSs are assembled as highly ordered linear chains on 2D rectangular micro-sheets by polydimethylsiloxane-wrinkle assisted assembly. Upon rolling the micro-sheets to micro-tubules, the AuNS chains transform into 3D helices. The AuNS-assembled helices induce collective plasmonic modes propagating in a helical manner, leading to a strong chiral response over the vis-NIR range. The circular dichroism (CD) is measured to be as high as hundreds of millidegree, and the position and sign of CD peaks are actively modulated by controlling the orientated angle of AuNS chains, enabled by tuning the collective plasmonic modes. This micro-origami-based strategy incorporates the incompatible 2D assembly technique with 3D chiral structures, opening up an intriguing way toward constructing chiral plasmonic structures and modulating chiroptical effects based on responsive polymeric materials.

Mechanisms of chiral plasmonics-Scattering, absorption, and photoluminescence.

Chirality is a concept that one object is not superimposable on its mirror image by translation and rotation. In particular, chiral plasmonics have been widely investigated due to their excellent optical chiral properties, and have led to numerous applications such as optical polarizing element etc. In this study, we develop a model based on the concept of the interaction between harmonic oscillators to investigate and explain the optical chiral mechanisms of strongly coupled metal nanoparticles (MNPs). The chirality of the scattering, absorption, and photoluminescence spectra are carefully discussed in detail. The results show that the chirality of the system originates not only from the orientations of the MNPs, but also from the different eigen parameters between them. Specifically, the derived three factors contribute to the chirality: the symmetry, the coupling strength, and the coherent superposition of the emitted electric field. This work provides a deeper understanding on the chiral plasmonics and may guide relevant applications in theory.

Quantitative analysis of circular dichroism at higher-order resonance of extrinsic plasmonic chiral nanostructures using multipole decomposition combined with the optical theorem

Plasmonic chirality, which has garnered significant attention in recent years due to its ability to generate strong near-field enhancement and giant circular dichroism (CD). Currently, various theories have been proposed to explain plasmonic extrinsic chirality, however, a comprehensively quantitative explanation for the high-order optical response of extrinsic metamolecule has yet to be established. Herein, we present a concise and quantitative explanation of the giant high-order extrinsic CD of a plasmonic nanocrescent, which origins from multipole decomposition in combination with the optical theorem. Our findings indicate that the high-order resonance modes exhibit giant CD comparable to dipolar modes and can be conveniently applied to the chiral recognition of metamolecules. Furthermore, the nonradiative electric quadrupole resonance exhibits enormous electric field enhancement near metamolecule, which has great application potential in the fields of molecular recognition and sensing in the visible region.

Plasmonic vortex beam emitter

Terahertz vortices prompt numerous advanced applications spanning classical and quantum communications, sensing, and chirality-based detection, owing to the inherent physical properties of terahertz waves and orbital angular momentum (OAM). Nonetheless, existing methodologies for generating terahertz vortices face challenges such as unalterable topological charges and intricate feed networks. To address these limitations, we propose a novel approach to generate multi-mode and tunable vortex beams based on chiral plasmons. Through eigenmode analysis, the uniform helical gratings are demonstrated to support chiral plasmons carrying OAM. By leveraging their vortex characteristics and introducing modulation into the periodic system, these chiral plasmons are alternatively diffracted into high-purity vortex radiations according to the Bragg law. To validate the theory, the vortex beam emitter is fabricated and measured in the microwave regime based on the modulated scheme. Experimental results confirm the emission of vortex beams with desirable phase distributions and radiation patterns. Our findings highlight the potential of chiral plasmons as seeds for tunable and compact vortex radiation, offering promising applications in tunable vortex sources.

Amino Acid‐Modulated Chirality Evolution and Highly Enantioselective Chiral Nanogap‐Enhanced Raman Scattering

AbstractControlling the growth and selection of chiral inducers is crucial for the generation of chiral inorganic structures as observed in nature. Herein, the plasmonic chirality evolution from the Au cube seed under the presence of L‐ or D‐amino acid as a chiral inducer is reported. The 432 Helicoid I structure is obtained using tryptophan (Trp), identical to the result with cysteine (Cys). The use of tyrosine (Tyr) produced a Helicoid IV‐type structure. However, no distinctive chiral structures can be obtained using phenylalanine (Phe), valine (Val) and leucine (Leu), which indicates the critical role of amino acids in chirality evolution. In particular, Trp‐Helicoid I nanoparticles (NPs) showed excellent enantioselective response toward L‐ or D‐Cys in the colorimetric assay and Raman analysis in the presence of Trp. Furthermore, the chiroptical property with a nanogap of 23.78 ± 0.82 nm in the Helicoid I structure further expands its applications for highly sensitive and quantitative chiral analysis for small molecules such as R/S‐epichlorohydrin (ECH), R/S‐limonene (LM), and R/S‐2‐butanol (BuOH) using a non‐polarized light source. The finding of amino acid‐dependent chirality evolution can widen the current understanding of chirality evolution in nature, and the use of helicoid structures with nanogaps incorporated with surface‐enhanced Raman scattering (SERS) can open a new avenue for chiral spectroscopic analysis.

Charge-transfer complexation: A highly effective way towards chiral nanoparticles endowed by intrinsically chiral helicene and enantioselective SERS detection

An ordered chiral gold nanoparticle (AuNPs) array was prepared by the treatment of achiral sphere-shaped gold nanoparticles endowed with electron-accepting dinitro-phenyl (DNP) groups complexing with enantiomers of [6]helicene representing electron donors with strong chiroptical properties. Such surface-functionalization utilizes the principles of charge-transfer (CT) interaction. The incorporation of [6]helicene molecules with unique electronic and optical properties and subsequent arrangement of AuNPs caused chirality induction to intrinsically non-chiral plasmon-active nanostructures. The created nanostructures enabled the excitation of chiral plasmon and its application in highly sensitive enantioselective detection of small chiral molecules by surface-enhanced Raman spectroscopy (SERS). The chiral plasmonic response of such a system was shown to be fully controlled via the helicity of the parent [6]helicene. Upon calibration, it allowed us to directly determine the enantiomeric composition of non-racemic mixtures of (R)/(S)− 1-phenylethanol and (R)/(S)− 2-butanol.

High Figure of Merit Refractive Index Sensor Derived From the Axial Length Ratio of Elliptically Polarized Light of Chiral Plasmonic Structure Arrays

High Figure of Merit Refractive Index Sensor Derived From the Axial Length Ratio of Elliptically Polarized Light of Chiral Plasmonic Structure Arrays

Chiral AuCu heterostructures with site-specific geometric control and tailored plasmonic chirality

Chiral AuCu heterostructures with site-specific geometric control and tailored plasmonic chirality

Coated Chiral Plasmonic Nanorods with Enhanced Structural Stability

Coated Chiral Plasmonic Nanorods with Enhanced Structural Stability

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

Enriching the library of chiral plasmonic nanoparticles that can be chemically mass-produced will greatly facilitate the applications of chiral plasmonics in areas ranging from constructing optical metamaterials to sensing chiral molecules and activating immune cells. Here we report on a halide-assisted differential growth strategy that can direct the anisotropic growth of chiral Au nanoparticles with tunable sizes and diverse morphologies. Anisotropic Au nanodisks are employed as seeds to yield triskelion-shaped chiral nanoparticles with threefold rotational symmetry and high dissymmetry factors. The averaged scattering g-factors of the l- and d-nanotriskelions are as large as 0.57 and − 0.49 at 650 nm, respectively. The Au nanotriskelions have been applied in chiral optical switching devices and chiral nanoemitters. We also demonstrate that the manipulation of the directional growth rate enables the generation of a variety of chiral morphologies in the presence of homochiral ligands.

Dynamics of optical vortices in van der Waals materials

Quantized vortices are topological defects found in different two-dimensional geometries, from liquid crystals to ferromagnets, famously involved in spontaneous symmetry breaking and phase transitions. Their optical counterparts appear in planar geometries as a universal wave phenomenon, possessing topologically protected orbital angular momentum (OAM). So far, the spatiotemporal dynamics of optical vortices, including vortex-pair creation and annihilation, has been observed only in Bose–Einstein condensates. Here we observe optical vortices in van der Waals materials and measure their dynamics, including events of pair creation and annihilation. Vortices of opposite OAM are involved in pair creation/annihilation events, and their relative signs determine the surrounding field profile throughout their motion. The vortices are made of phonon polaritons in hexagonal boron nitride, which we directly probe using free electrons in an ultrafast transmission electron microscope. Our findings promote future investigations of vortex phenomena in van der Waals platforms, toward their use for chiral plasmonics, quantum simulators, and control over selection rules in light–matter interactions.