Plasmonic Interactions at Close Proximity in Chiral Geometries: Route toward Broadband Chiroptical Response and Giant Enantiomeric Sensitivity (original) (raw)
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Nano Letters, 2012
We report a new approach for creating chiral plasmonic nanomaterials. A previously unconsidered, far-field mechanism is utilized which enables chirality to be conveyed from a surrounding chiral molecular material to a plasmonic resonance of an achiral metallic nanostructure. Our observations break a currently held preconception that optical properties of plasmonic particles can most effectively be manipulated by molecular materials through near-field effects. We show that far-field electromagnetic coupling between a localized plasmon of a nonchiral nanostructure and a surrounding chiral molecular layer can induce plasmonic chirality much more effectively (by a factor of 10 3) than previously reported near-field phenomena. We gain insight into the mechanism by comparing our experimental results to a simple electromagnetic model which incorporates a plasmonic object coupled with a chiral molecular medium. Our work offers a new direction for the creation of hybrid molecular plasmonic nanomaterials that display significant chiroptical properties in the visible spectral region.
Plasmonic nanoparticle monomers and dimers: from nanoantennas to chiral metamaterials
2011
We review the basic physics behind light interaction with plasmonic nanoparticles. The theoretical foundations of light scattering on one metallic particle (a plasmonic monomer) and two interacting particles (a plasmonic dimer) are systematically investigated. Expressions for effective particle susceptibility (polarizability) are derived, and applications of these results to plasmonic nanoantennas are outlined. In the longwavelength limit, the effective macroscopic parameters of an array of plasmonic dimers are calculated. These parameters are attributable to an effective medium corresponding to a dilute arrangement of nanoparticles, i.e., a metamaterial where plasmonic monomers or dimers have the function of "meta-atoms". It is shown that planar dimers consisting of rod-like particles generally possess elliptical dichroism and function as atoms for planar chiral metamaterials. The fabricational simplicity of the proposed rod-dimer geometry can be used in the design of more cost-effective chiral metamaterials in the optical domain.
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.
Scientific reports, 2016
Extrinsic or pseudo-chiral (meta)surfaces have an achiral structure, yet they can give rise to circular dichroism when the experiment itself becomes chiral. Although these surfaces are known to yield differences in reflected and transmitted circularly polarized light, the exact mechanism of the interaction has never been directly demonstrated. Here we present a comprehensive linear and nonlinear optical investigation of a metasurface composed of tilted gold nanowires. In the linear regime, we directly demonstrate the selective absorption of circularly polarised light depending on the orientation of the metasurface. In the nonlinear regime, we demonstrate for the first time how second harmonic generation circular dichroism in such extrinsic/pseudo-chiral materials can be understood in terms of effective nonlinear susceptibility tensor elements that switch sign depending on the orientation of the metasurface. By providing fundamental understanding of the chiroptical interactions in ac...
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.
Engineering of radiation of optically active molecules with chiral nano-meta-particles
EPL (Europhysics Letters), 2012
The radiation of optically active (chiral) molecule placed near chiral nanosphere is investigated. The optimal conditions for engineering of radiation of optically active (chiral) molecules with the help of chiral nanoparticles are derived. It is shown that for this purpose, the substance of the chiral particle must have both ε and µ negative (double negative material (DNG)) or negative µ and positive ε (µ negative material (MNG)). Our results pave the way to an effective engineering of radiation of "left" and "right" molecules and to creating pure optical devices for separation of drugs enantiomers.
The origin of off-resonance non-linear optical activity of a gold chiral nanomaterial
Nanoscale, 2013
We demonstrate that engineered artificial gold chiral nanostructures display significant levels of non-linear optical activity even without plasmonic enhancement. Our work suggests that although plasmonic excitation enhances the intensity of second harmonic emission it is not a prerequisite for significant non-linear (second harmonic) optical activity. It is also shown that the non-linear optical activities of both the chiral nanostructures and simple chiral molecules on surfaces have a common origin, namely pure electric dipole excitation. This is a surprising observation given the significant difference in length scales, three orders of magnitude, between the nanostructures and simple chiral molecules. Intuitively, given that the dimensions of the nanostructures are comparable to the wavelength of visible light, one would expect non-localised higher multipole excitation (e.g. electric quadrupole and magnetic dipole) to make the dominant contribution to non-linear optical activity. This study provides experimental evidence that the electric dipole origin of non-linear optical activity is a generic phenomenon which is not limited to sub-wavelength molecules and assemblies. Our work suggests that viewing nonplasmonic nanostructures as "meta-molecules" could be useful for rationally designing substrates for optimal non-linear optical activity.
Tunable chiroptical response of chiral system composed of a nanorod coupled with a nanosurface
Applied Surface Science, 2019
Artificially engineered chiral plasmonic nanostructures (CPNs) have attracted considerable attention and have been widely studied in the recent decades because of their distinguishing optical properties. Researchers have focused on noble metal nanostructures, because of their strong chiroptical response in visible and near-infrared regions. In this study, a system of a nanorod coupled with a nanosurface, which were both made of silver, was proposed. Glancing angle deposition (GLAD) method was used to fabricate CPNs. The fabricated CPNs generated a strong circular dichroism (CD) signal under visible and near-infrared light illumination. A high peak was observed at approximately 600 nm, and an increasing trend of the CD intensity with a redshift was confirmed when the area of the nanosurface was increased. The generated CD could be tuned easily by changing the area of the nanosurface with an active control of the vapor deposition angle (glancing angle of the substrate) in the GLAD method.
Physical Review A
We present the characteristics of a simple waveguiding structure constructed by anisotropic birefringent crystal-metal-chiral medium, anisotropic metal chiral in short, and reveal the chiral-dependent dispersion and propagation properties of the surface plasmon polaritons (SPPs). We demonstrate its unprecedented discrimination ability to the magnitude and sign of both the real and imaginary part of the chirality parameter. The anisotropy plays a key role in such performance and shows tunable ability in enantiomeric discrimination even when the chirality parameter is complex valued. Most importantly, the physical origin of chiral discrimination stems from the extrinsic chirality of the system, which arises from the mutual orientation of the SPPs and the optical axis. Moreover, we also clarify the fundamental physics behind the chiral sensing behavior by associating the intrinsic quantum spin Hall effect of the SPPs with the electromagnetic field analysis. This structure does not rely on complicated fabrication but provides the opportunity of on-chip surface-sensitive biosensing. We anticipate that our work will stimulate intensive research to investigate the anisotropy-induced chiral sensing techniques in plasmonic platforms.