Tunable chiroptical response of chiral system composed of a nanorod coupled with a nanosurface (original) (raw)
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Optics Express, 2021
Chiral molecules are ubiquitous in nature; many important synthetic chemicals and drugs are chiral. Detecting chiral molecules and separating the enantiomers is difficult because their physiochemical properties can be very similar. Here we review the optical approaches that are emerging for detecting and manipulating chiral molecules and chiral nanostructures. Our review focuses on the methods that have used plasmonics to enhance the chiroptical response. We also review the fabrication and assembly of (dynamic) chiral plasmonic nanosystems in this context.
Giant Tunable Circular Dichroism of Large-Area Extrinsic Chiral Metal Nanocrescent Arrays
Nanoscale Research Letters
Circular dichroism (CD) is an interesting phenomenon originating from the interaction of light with chiral molecules or other nanostructures lacking mirror symmetries in three-dimensional (3D) or two-dimensional (2D) space. While the observable effects of optical chirality are very weak in most of the natural materials, they can be designed and significantly enhanced in synthetic chiral structures, where the spatial symmetry of their component are broken on a nanoscale. Therefore, fabrication of composites capable of cheap, time-saving, and giant CD is desirable for the advanced optical technologies. Here, the giant CD of large-area metal nanocrescent array structures was investigated theoretically and experimentally. The largest value of the CD spectrum measured was larger than 0.5, and the CD spectrum was tuned effectively and extensively while maintaining a large peak intensity, which can be attributed to the selective excitation of the lattice surface modes (LSMs) by circularly ...
Plasmonic ratchet wheels: switching circular dichroism by arranging chiral nanostructures
Nano letters, 2009
We demonstrate circular dichroism (CD) in the second harmonic generation (SHG) signal from chiral assemblies of G-shaped nanostructures made of gold. The arrangement of the G shapes is crucial since upon reordering them the SHG-CD effect disappears. Microscopy reveals SHG "hotspots" assemblies, which originate in enantiomerically sensitive plasmon modes, having the novel property of exhibiting a chiral geometry themselves in relation with the handedness of the material. These results open new frontiers in studying chirality.
A General Mechanism for Achieving Circular Dichroism in a Chiral Plasmonic System
Annalen der Physik, 2018
Chiral plasmonic (CP) systems are shown to exhibit effectual circular dichroism (CD). A general mechanism based on the Jones matrix for predicting the CD signal of CP systems is proposed. Considering the near-field coupling of adjacent layers of trilayer CP systems, the coupling matrix, which shows the relevance of the coupling status to the relative position of the adjacent layers, is analytically derived under the framework of the transfer matrix method. To prove the coupling matrix, a trilayer system is designed, and the optical properties of the relevant system arrays are simulated using the finite-element method. The fitting functions of the simulated CD signals at resonant wavelengths are consistent with the theoretical formulas. The proposed mechanism facilitates an understanding of the underlying physical mechanism of CD and offers a design principle for fabrication of CP systems that are applicable to biosensing.
Intense Optical Activity from Three-Dimensional Chiral Ordering of Plasmonic Nanoantennas
Angewandte Chemie International Edition, 2011
Noble-metal nanoparticles with localized surface-plasmon resonances (LSPR) have been recently used to prepare new materials with improved optical circular dichroism. This interest stems from a wide range of applications in biology and physics, including the structural determination of proteins and DNA and the pursuit of negative refraction. Surfaceplasmon-mediated circular dichroism (SP-CD) in solution has been explored to date using small spherical metal particles, invariably resulting in moderate signals over a narrow spectral range. In contrast, we present herein a novel class of metamaterial consisting of gold nanorods (NRs) organized in three-dimensional (3D) chiral structures and yielding a record circular dichroism anisotropy factor for metal nanoparticles (> 0.02) across visible and near-infrared (Vis-NIR) wavelengths (600-900 nm). The fabrication process can be easily upscaled, as it involves the self-assembly of gold nanorods on a fiber backbone with chiral morphology. Our measurements are fully supported by theoretical modeling based on coupled dipoles, unraveling the key role of gold nanorods in the chiroptical response.
The Journal of Physical Chemistry C, 2014
Chiral metamaterials can have diverse technological applications, such as engineering strongly twisted local electromagnetic fields for sensitive detection of chiral molecules, negative indices of refraction, broadband circular polarization devices, and many more. These are commonly achieved by arranging a group of noble-metal nanoparticles in a chiral geometry, which, for example, can be a helix, whose chiroptical response originates in the dynamic electromagnetic interactions between the localized plasmon modes of the individual nanoparticles. A key question relevant to the chiroptical response of such materials is the role of plasmon interactions as the constituent particles are brought closer, which is investigated in this paper through theoretical and experimental studies. The results of our theoretical analysis, when the particles are brought in close proximity are dramatic, showing a large red shift and enhancement of the spectral width and a near-exponential rise in the strength of the chiroptical response. These predictions were further confirmed with experimental studies of gold and silver nanoparticles arranged on a helical template, where the role of particle separation could be investigated in a systematic manner. The "optical chirality" of the electromagnetic fields in the vicinity of the nanoparticles was estimated to be orders of magnitude larger than what could be achieved in all other nanoplasmonic geometries considered so far, implying the suitability of the experimental system for sensitive detection of chiral molecules.
IEEE Photonics Journal, 2017
Through a numerical study, we proposed and demonstrated that the onedimensional periodic plasmonic-grooves (1D-PPG) can give rise to a super chiral field inside grooves under normal illumination with off-groove linear polarization. The handedness of the optical chirality of chiral field can be reversed by modifying the incident polarization angle from + 45°relative to groove's period direction to its mirror-symmetrical angle −45°. This makes possible a novel sensing scheme that utilize this polarization-dependent local chiral field for circular dichroism detecting; meanwhile, the dielectric environment-sensitive plasmonic resonance of 1D-PPG can be employed for refractive index sensing. This dualsensing strategy offers great potential for low-cost chirality sensing for chiral molecules.
Macroscopic Layers of Chiral Plasmonic Nanoparticle Oligomers from Colloidal Lithography
Optical near-field coupling between closely spaced plasmonic metal nanoparticles is important to a range of nanophotonic applications of high contemporary interest, including surface-enhanced molecular spectroscopy, nanooptical sensing, and various novel light-harvesting concepts. Here we report on monolayers of chiral heterotrimers and heterotetramers composed of closely spaced silver and/or gold nanodisks of different heights fabricated through facile hole-mask colloidal lithography. These quasi-three-dimensional oligomers are interesting for applications because they exhibit ?hot? gaps and crevices of nanometric dimensions, a pronounced circular dichroism, and optical chirality in the visible to near-infrared wavelength range, and they can be produced in large ensembles (>109) of identical orientation. We analyze the optical properties of the samples based on simulation results and find that the circular dichroism is due to strong near-field coupling and intricate phase retard...