Plasmonic Molecules Research Articles

Fabrication of Plasmonic Nano-Aperture Platform for Singe-Molecule Detection and Self-Cooling Thermal Emission

In this report, the optical emission characteristics from the nano-apertures on the Au nano-plasmonic platform will be reported. Regardless of the nano-aperture type of either circular type or nanoslit type, the spp-mediated optical emission characteristics dependent upon the sample thickness and aperture size are observed. However, the spp mediated optical characteristics are found to be increasing with decreasing the aperture size, and to be independent of the nano-aperture shape, which observation fits to Lord Raleigh’s diffraction theory of small particle with its size much smaller than the wavelength and Babinet principle. The fabricated nanometer slit arrays with its size of (~10 nm width and ~ 300 nm length) with its optical characterization are provided in Figure 1. The fabricated platform device can be utilized as various applications such as plasmonic single molecule sensors and plasmomic self- cooling device from its broad emission spectra from visible to infrared regime. Figure 1

Astemizole as a drug to inhibit the effect of SARS-COV-2 in vitro

Since the beginning of December 2019, a novel Coronavirus severe respiratory disease, caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) which also been termed 2019-new CoV (2019-nCoV), has continued to spread worldwide. As of August 27, 2020, a total of 24,232,429 people have been infected and 826,518 people have died. In our study, we found that astemizole can antagonize ACE2 and inhibit the entry of SARS-COV-2 spike pseudovirus into ACE2-expressed HEK293T cells (ACE2hi cells). We analysied the binding character of astemizole to ACE2 by molecular docking and surface plasmon resonance (SPR) assays and molecule docking, SARS-COV-2 spike pseudotype virus was also taken to investigate the suppression viropexis effect of astemizole. The results showed that astemizole can bind to the ACE2 receptor and inhibit the invasion of SARS-COV-2 Spike pseudoviruses. Thus astemizole represent potential drug candidates that can be re-used in anti-coronavirus therapies.

Plasmon–Molecule Coupling with Directional Absorption Features: A First-Principles Study

The coupling between plasmonic nanocavity and quantum emitters has been a major focus of quantum optics and material science research over the last few years. In this work, using state-of-the-art first-principles calculations, we investigate the spatial distributions of the induced charge density and electric near-field enhancements of a nanosystem consisting of an aluminum nanotriangle interacting with the varying number of benzene molecules positioned at the nanotriangle tips. We find interesting modifications in the induced charge density and electric near-field enhancements with a remarkable sensitivity to the number of interacting benzene molecules and to the direction of light illumination. In a broader perspective, our quantum mechanical results provide quantitative access to the electric near-field enhancements at the nanoscale useful for designing ultra-small plasmonic devices.

Light-Responsive Dynamic DNA-Origami-Based Plasmonic Assemblies.

DNA nanotechnology offers a versatile toolbox for precise spatial and temporal manipulation of matter on the nanoscale. However, rendering DNA‐based systems responsive to light has remained challenging. Herein, we describe the remote manipulation of native (non‐photoresponsive) chiral plasmonic molecules (CPMs) using light. Our strategy is based on the use of a photoresponsive medium comprising a merocyanine‐based photoacid. Upon exposure to visible light, the medium decreases its pH, inducing the formation of DNA triplex links, leading to a spatial reconfiguration of the CPMs. The process can be reversed simply by turning the light off and it can be repeated for multiple cycles. The degree of the overall chirality change in an ensemble of CPMs depends on the CPM fraction undergoing reconfiguration, which, remarkably, depends on and can be tuned by the intensity of incident light. Such a dynamic, remotely controlled system could aid in further advancing DNA‐based devices and nanomaterials.

Light‐Responsive Dynamic DNA‐Origami‐Based Plasmonic Assemblies

AbstractDNA nanotechnology offers a versatile toolbox for precise spatial and temporal manipulation of matter on the nanoscale. However, rendering DNA‐based systems responsive to light has remained challenging. Herein, we describe the remote manipulation of native (non‐photoresponsive) chiral plasmonic molecules (CPMs) using light. Our strategy is based on the use of a photoresponsive medium comprising a merocyanine‐based photoacid. Upon exposure to visible light, the medium decreases its pH, inducing the formation of DNA triplex links, leading to a spatial reconfiguration of the CPMs. The process can be reversed simply by turning the light off and it can be repeated for multiple cycles. The degree of the overall chirality change in an ensemble of CPMs depends on the CPM fraction undergoing reconfiguration, which, remarkably, depends on and can be tuned by the intensity of incident light. Such a dynamic, remotely controlled system could aid in further advancing DNA‐based devices and nanomaterials.

Shell-Isolated Au Nanoparticles Functionalized with Rhodamine B Fluorophores in Helium Nanodroplets.

Nanoparticles consisting of three different materials in a layered core@shell@shell structure are synthesized in cold helium droplets by sequential doping. Upon the formation of Au core particles, a first shell layer is formed by adding either Ar, isopropyl alcohol, or hexane. Subsequently, the droplets are doped with rhodamine B (RB) molecules; fluorescence spectra recorded upon laser excitation at 532 nm provide insight into the structure of the formed complexes. For the two-component Au@RB system, the RB fluorescence is quenched in the presence of the Au core. If an intermediate isolating shell layer is introduced (Au@shell@RB), the fluorescence increases again. The results demonstrate that shell-isolated nanoparticles can be formed inside He nanodroplets and functionalized in situ with additional molecules. As the structure of the particles depends on the pickup sequence, the approach can be exploited for the synthesis and investigation of a large variety of different combinations of plasmonic metals, intermediate layers, and molecules.

Enhanced Graphene Plasmonic Mode Energy for Highly Sensitive Molecular Fingerprint Retrieval

AbstractGraphene plasmons with tightly confined fields and actively tunable resonant frequencies enable the selective detection of molecular vibrational fingerprints with ultrahigh sensitivity, significantly promoting the development of surface‐enhanced infrared absorption spectroscopies (SEIRAS). However, current experimentally obtained enhancements are much smaller than the theoretical prediction due to the extremely low graphene plasmonic mode energy. In this paper, the strategies to improve the mode energy are theoretically and experimentally investigated in a one‐port graphene plasmonic system. By optimizing the Fabry–Pérot cavity length and employing multi‐layer graphene to drive the system into the near critical coupling regime, the localized graphene plasmonic absorptions can be improved from 3% to more than 92%. This induces a 37 times improvement of graphene plasmonic mode energy from 0.4 × 10−13 to 1.5 × 10−12 J per period for the strong plasmon–molecule interactions, enabling the highly sensitive detection of 8 nm thick molecular film. The SEIRAS experimental results demonstrate that a maximum enhancement factor of 162 can be achieved, which is one order larger than that of the reported localized graphene plasmonic sensors. The results showcase the practical usability of localized graphene plasmons for the next‐generation high sensitive nanoscale infrared spectroscopy.

Double-Resonant Plasmonic Molecule: Enhanced Vibrational Induced Scattering Modulation

The present publication investigates the optical scattering behavior of an artificial near-field coupled double-resonant plasmonic molecule on a glass substrate formed by a linear arrangement of three gold nanobars. The aim of the proposed symmetrical structure arrangement is to achieve a significant increase in the feedback of optically induced coherent mechanical oscillations on the scattering cross-section. Based on the description of isolated dipole-like plasmonic nanostructures, it is shown how an increase of the modulation strength can be achieved by systematic utilization and modification of the inherent near-field coupling effect. It is shown which differences exist compared to an isolated plasmonic nanostructure, especially for the NIR spectral range. To the best of our knowledge, this is the first investigation showing the behavior of coherent acoustic vibrations in such artificial plasmonic molecules at an optical carrier wavelength of 1560 nm which is particularly interesting for applications in the field of optical communication.

Alternating Coupling Regimes in a Plasmon–Molecule Hybrid Structure through a Phase-Change Material

Plasmon–molecule hybrid systems provide platforms for studying light–matter interactions. It is of great interest for systems where both strong and weak plasmon–molecule couplings exist and can transfer into each other freely. In this paper, we proposed a hybrid structure composed of a vanadium dioxide (VO2) layer sandwiched between a polymethyl methacrylate (PMMA) strip array and a gold substrate. The molecular vibration of PMMA interacts with the surface plasmon polaritons (SPPs) of the metal substrate, and the coupling regimes can be alternated through the phase transition of VO2. The electric fields at SPP resonances closely relate with the optical properties of VO2. When VO2 is an insulator, high electric fields in PMMA strips cause the strong plasmon–molecule coupling and new hybrid modes are formed. When VO2 is a metal, the electric fields in PMMA are moderate due to high loss of metallic VO2 and the plasmon–molecule coupling is in the weak coupling regime. The influence of the VO2 layer thickness on coupling properties was also discussed in detail for VO2 in different phases. Our study provides a new strategy to modulate the plasmon–molecule coupling and is inspiring for fundamental and practical research studies on light–matter interactions.

Strongly coupled evenly divided disks: a new compact and tunable platform for plasmonic Fano resonances

Plasmonic artificial molecules are promising platforms for linear and nonlinear optical modulation at various regimes including the visible, infrared and terahertz bands. Fano resonances in plasmonic artificial structures are widely used for controlling spectral lineshapes and tailoring of near-field and far-field optical response. Generation of a strong Fano resonance usually relies on strong plasmon coupling in densely packed plasmonic structures. Challenges in reproducible fabrication using conventional lithography significantly hinders the exploration of novel plasmonic nanostructures for strong Fano resonance. In this work, we propose a new class of plasmonic molecules with symmetric structure for Fano resonances, named evenly divided disk, which shows a strong Fano resonance due to the interference between a subradiant anti-bonding mode and a superradiant bonding mode. We successfully fabricated evenly divided disk structures with high reproducibility and with sub-20 nm gaps, using our recently developed sketch and peel lithography technique. The experimental spectra agree well with the calculated response, indicating the robustness of the Fano resonance for the evenly divided disk geometry. Control experiments reveal that the strength of the Fano resonance gradually increases when increasing the number of split parts on the disk from three to eight individual segments. The Fano-resonant plasmonic molecules that can also be reliably defined by our unique fabrication approach open up new avenues for application and provide insight into the design of artificial molecules for controlling light-matter interactions.

Mechanism of visible light enhanced catalysis over curcumin functionalized Ag nanocatalysts.

There is little research on the visible light photocatalytic properties of the hybrids of plasmonic metals and organic molecules (OM) with the HOMO-LUMO gap in the visible range. Here, we investigate the mechanism of the visible light enhanced reduction of p-nitrophenol (PNP) by glycerol (a green reductant) at ambient temperature over curcumin functionalized Ag nanoparticles (c-AgNPs). The catalytic activity got significantly boosted under visible light irradiation. Reaction kinetics indicated that the catalytic mechanism followed under visible light and in the dark were different. DFT calculations showed that in the ground state, the HOMO resides on Ag while the LUMO is on the curcumin part of the composite. TD-DFT calculations demonstrated the transfer of charge from Ag to curcumin on photo-excitation. Based on this information, we propose a mechanism for understanding the role of curcumin in this photocatalytic phenomenon.

Visible light from modulated electron beam moving between twin circular silver nanowires forming plasmonic photonic molecule

The visible-range diffraction radiation of harmonically modulated electron beam, which moves between twin circular silver nanowires, is considered. The electromagnetic field of such a two-dimensional beam is a surface wave propagating along its trajectory with the phase velocity equal to the beam velocity. This wave induces currents on the nanowires and hence radiation occurs even if the beam does not touch the wires. If the wires are tuned to a resonance, the radiated power displays a peak proportional to the resonant mode Q-factor. Sub-wavelength in radius silver nanowires are famous as nanoresonators due to the localized surface-plasmon modes. In our analysis, we use the field expansions in the azimuthal Fourier series and the addition theorems for the cylindrical functions. This enables us to reduce the wave scattering problem to a Fredholm second kind infinite-matrix equation that guarantees convergence of numerical solutions. Truncating this matrix, we compute the near and far field patterns of the wires as optically coupled plasmonic resonators and analyze dependence of the far-field spectral characteristics on the wavelength and electron beam parameters.

Galvanic Replacement Reaction as a Route to Prepare Nanoporous Aluminum for UV Plasmonics.

There is a growing interest in extending plasmonics applications into the ultraviolet region of the electromagnetic spectrum. Noble metals are commonly used in plasmonic, but their intrinsic optical properties limit their use above 350 nm. Aluminum is probably the most suitable material for UV plasmonics, and in this work we fabricated substrates of nanoporous aluminum starting from an alloy of Al2Mg3. The porous metal is obtained by means of a galvanic replacement reaction. Such nanoporous metal can be exploited to achieve a plasmonic material suitable for enhanced UV Raman spectroscopy and fluorescence. Thanks to the large surface to volume ratio, this material represents a powerful platform for promoting interaction between plasmonic substrates and molecules in the UV.

Plasmon-driven protodeboronation reactions in nanogaps.

Boronic acids are the key compounds in Suzuki coupling reactions and in the detection of monosaccharides. The C-B bond cleavage deboronation is an important side reaction that lowers the Suzuki coupling reaction yield and even disables saccharide detection. Here, we report that protodeboronation occurs for 4-mercaptophenylboronic acid (MPBA) within narrow nanogaps between gold nanoparticles (AuNPs) and planar gold substrates. The irradiation of such nanoparticle-on-mirror (NPoM) systems at 785 nm drives the protodeboronation reaction to form benzenethiol (BT). Wavelength-dependence experiments, combined with dark-field single-particle scattering spectroscopy, reveal that excitation of the bonding dipole plasmon mode of the NPoM leads to the best efficiency. Among the excited plasmon decay pathways, the generation of hot charge carriers induces the protodeboronation of MPBA. The possibility of plasmonic thermal reactions is ruled out because external heating of the substrates does not cause the reaction to take place. A comparison of the reaction yield under ambient, Ar, and oxygen gas conditions reveals that hot charge carriers directly transfer to MPBA, which subsequently produces BT, but the presence of oxygen promotes the reaction by opening another hot-electron transfer channel. The protodeboronation reaction of MPBA is an important addition to the catalog of plasmon-driven chemical reactions, not only because the reaction is relevant to organic and analytical chemistry but also because it deepens our understanding of the hot carrier dynamics at the interface between plasmonic nanoparticles and molecules.

Double Fano resonances in hybrid disk/rod artificial plasmonic molecules based on dipole-quadrupole coupling.

Fano resonance can be achieved by the destructive interference between a superradiant bright mode and a subradiant dark mode. A variety of artificial plasmonic oligomers have been fabricated to generate Fano resonance for its extensive applications. However, the Fano resonance in plasmonic oligomer systems comes from the interaction of all metal particles, which greatly limits the tunability of the Fano resonance. Besides, only a single Fano resonance is supported by many existing plasmonic oligomers, while multiple Fano resonances mostly occur in complex and multilayer structures, whose fabrication is greatly challenging. Here, a simple asymmetric plasmonic molecule consisting of a central metal disk and two side-coupled parallel metal rods is demonstrated. The simulation and experimental results clearly show that double Fano resonances appear in the transmission spectrum. In addition, the two Fano peaks can be independently tuned and single/double Fano peak switching can be achieved by changing one rod length or the gap distances between the rods and the disk. The modulation method is simple and effective, which greatly increases the tunability of the structure. The proposed asymmetric artificial plasmonic molecule can have applications in multi-channel optical switches, filters and biosensors. Moreover, the controllable plasmonic field intensity in the gap between the disk and rods also provides a new control means for plasmon-induced photocatalytic reactions and biosynthesis.

Plasmonic Nanomolecules: Electrochemical Resolution of 22 Electronic States in Au329(SR)84

Gold nanomolecules are atomically precise gold thiolate nanoparticles. They show size-dependent optical and electrochemical properties due to the quantization effects. The optical properties are well explored. However, there is still a void in understanding their electrochemical properties and probing higher oxidation states. We report the 22 electronic states of a plasmonic nanocrystal molecule with 329 gold atoms and 84 phenylethanethiolate ligands in a wide electrochemical potential (∼4 V) window. We provide a comprehensive understanding of the electrochemical properties as a function of size and composition of gold nanomolecules. This report also demonstrates that they behave like quantum capacitors and their capacitance varies linearly with size. The effect of ligand monolayer and core composition on the electrochemical properties was demonstrated using a 144-metal atom system. These results would help us design applications using the gold and alloy nanomolecules in photovoltaics, catalysis, sensors, and energy storage devices.

Metasurfaces Composed of Plasmonic Molecules: Hybridization Between Parallel and Orthogonal Surface Lattice Resonances

AbstractMultiple surface lattice resonances suppress radiative losses effectively around several spectral positions, thereby enhancing the light‐matter interactions and making them promising for multiwavelength related applications, and it is important to develop reliable methods to generate multiple lattice resonances. In analogy to natural materials composed of various kinds of molecules, this study proposed to construct metasurfaces with plasmonic artificial molecules, which represent distinct collective responses compared with that of single nanoparticles. It is shown that sharp multiple surface lattice resonances are excited due to the coupling between the localized resonances of plasmonic trimer molecules and the Rayleigh anomalies of the array, and there is a rarely observed parallel lattice resonance caused by the formation of equivalent dipoles perpendicular to the polarization. Particularly, even though the parallel mode is weak, a pronounced anticrossing behavior due to the hybridization with the orthogonal mode occurs when the resonance energies are approaching to each other, which results in two hybridized eigenmodes that possess both characteristics of parallel and orthogonal Rayleigh anomalies. Considering the excitation of the lattice resonances in asymmetric environments, the flexible tunability, and the ability to tailor the collective responses, metasurfaces constructed with artificial molecules are promising platforms to design ultrafast and compact photonic devices.

DNA-Enabled Chiral Gold Nanoparticle-Chromophore Hybrid Structure with Resonant Plasmon-Exciton Coupling Gives Unusual and Strong Circular Dichroism.

Circular dichroism (CD) from hybrid complexes of plasmonic nanostructures and chiral molecules has recently attracted significant interest. However, the hierarchical chiral self-assembly of molecules on surfaces of metal nanostructures has remained challenging. As a result, a deep understanding of plasmon-exciton coupling between surface plasmons and chiral collective molecular excitations has not been achieved. In particular, the critical impact of resonant plasmon-exciton coupling within the hybrid is unclear. Here, we employed DNA-templated strategies to control the chiral self-assembly of achiral chromophores with rationally tuned exciton transitions on gold nanosphere (AuNP) or gold nanorod (AuNR) surfaces. Unlike many previous chiral plasmonic hybrids utilizing chiral biomolecules with CD signals in the UV range, we designed structures with the chiral excitonic resonances at visible wavelengths. The constructed hybrid complexes displayed strong chiroptical activity that depends on the spectral overlap between the chiral collective molecular excitations and the plasmon resonances. We find that when spectral overlap is optimized, the molecular CD signal originating from the chiral self-assemblies of chromophores was strongly enhanced (maximum enhancement of nearly an order of magnitude) and a plasmonic CD signal was induced. Surprisingly, the sign of the molecular CD was reversed despite different self-assembly mechanisms of the Au nanoparticle-chromophore hybrids. Our results provide new insight into plasmonic CD enhancements and will inspire further studies on chiral light-matter interactions in strongly coupled plasmonic-excitonic systems.

Plasmon-driven high harmonic generation of benzene: effect of spatial inhomogenity of near field

When short and intense laser pulses interact with nanosystems which include plasmonic nanoparticles (NPs) and molecules, the laser induced spatially inhomogeneous near-fields modify the molecule’s electron dynamics. Consequently, this affects the high-order harmonic generation (HHG) processes. Although a lot of experimental and theoretical work have been devoted to study the plasmon-driven HHG processes of atoms or diatomic molecules, there are no clear pictures to show how the electronic trajectories and spectral characters vary with the locations of polyatomic molecules. Here we perform a comprehensive theoretical study on the coupled dynamics between the spatially inhomogeneous fields and matter by combining the computational electrodynamic model with the time-dependent density functional theory. The plasmon-driven electron dynamics and HHG spectra of a benzene molecule in the vicinity of a gold nanosphere or in the gap of a pair of nanospheres have been investigated. The unique phenomena arisen from the surface-enhanced near-field are described and the underlying mechanism which determines the salient features of plasmon-driven HHG is presented. Our study demonstrates that the HHG spectral features are sensitive to the molecule-NP’s distance and the incident light’s polarization, and that the intensities of lower-order harmonics follow an exponentially decay with the molecule-NP’s distance and the laser’s polarization direction. Additionally, we find that when the incident light frequency is resonant with plasmon excitation, the obvious phase difference between the x- and y -components of near fields makes the electronic trajectories obviously follow elliptical paths. However, that elliptically polarized light does not generate the strikingly different spectra due to the near field’s spatial inhomogeneity.

Arrays of Plasmonic Nanoparticle Dimers with Defined Nanogap Spacers.

Plasmonic molecules are building blocks of metallic nanostructures that give rise to intriguing optical phenomena with similarities to those seen in molecular systems. The ability to design plasmonic hybrid structures and molecules with nanometric resolution would enable applications in optical metamaterials and sensing that presently cannot be demonstrated, because of a lack of suitable fabrication methods allowing the structural control of the plasmonic atoms on a large scale. Here we demonstrate a wafer-scale "lithography-free" parallel fabrication scheme to realize nanogap plasmonic meta-molecules with precise control over their size, shape, material, and orientation. We demonstrate how we can tune the corresponding coupled resonances through the entire visible spectrum. Our fabrication method, based on glancing angle physical vapor deposition with gradient shadowing, permits critical parameters to be varied across the wafer and thus is ideally suited to screen potential structures. We obtain billions of aligned dimer structures with controlled variation of the spectral properties across the wafer. We spectroscopically map the plasmonic resonances of gold dimer structures and show that they not only are in good agreement with numerically modeled spectra, but also remain functional, at least for a year, in ambient conditions.