Plasmon Resonance Coupling Research Articles

The effect of nanorod position on the plasmonic properties of the complex nanorod in nanohole arrays

By moving the nanorod (NR) from the middle toward the rim of the nanohole (NH), i.e. breaking the geometric symmetry, the extraordinary optical transmission (EOT) caused by the dipole coupling of the localized surface plasmon resonance of the NR and the NH can be tuned to redshift exponentially while maintaining the high transmission and overall dimension of the structural unit. This resonant wavelength shift depends strongly on the moving direction of the NR, i.e. whether it is along the long axis or short axis of the rod. Connecting the NR to the NH and increasing the lattice period can significantly redshift the EOT mode, allowing ultra-high transmission in the mid-infrared (MIR) region. The high local E-fields, enhanced propagating waves with a tunable visible-MIR resonance wavelength, make this structure suitable for the design of compact and integrated optical devices from the visible to the MIR wavelength range. In addition, Fano resonances are emerging due to the coupling and hybridization of different plasmonic modes, making the structure beneficial for high sensitivity measurement.

Asymmetric flow field-flow fractionation coupled to surface plasmon resonance detection for analysis of therapeutic proteins in blood serum

Coupling of surface plasmon resonance (SPR) detection to asymmetric flow field-flow fractionation (AF4) offers the possibility to study active fractions of bio-separations on real samples, such as serum and saliva, including the assessment of activity of possibly aggregated species. The coupling of SPR with AF4 requires the possibility to select fractions from a fractogram and redirect them to the SPR. The combination of SPR with chromatography-like methods also requires a mechanism for regeneration of the receptor immobilised onto the SPR sensor surface. In recent work, the combination of size exclusion chromatography (SEC) with SPR was pioneered as a successful methodology for identification, characterisation and quantification of active biocomponents in biological samples. In this study, the approach using AF4 is evaluated for the antibody trastuzumab in buffer and serum. The particular object of this study was to test the feasibility of using AF4 in combination with SPR to detect and quantify proteins and aggregates in complex samples such as blood serum. Also, in the investigation, three different immobilisation methods for the receptor HER-2 were compared, which involved (1) direct binding via EDC/NHS, the standard approach; (2) immobilisation via NTA-Ni-Histag complexation; and (3) biotin/avidin-linked chemistry using a regenerable form of avidin. The highest specific activity was obtained for the biotin-avidin method, while the lowest specific activity was observed for the NTA-Ni-Histag linkage. The data show that AF4 can separate trastuzumab monomers and aggregates in blood serum and that SPR has the ability to selectively monitor the elution. This is an encouraging result for automated analysis of complex biological samples using AF4-SPR.

AlGaN Deep-Ultraviolet Light-Emitting Diodes with Localized Surface Plasmon Resonance by a High-Density Array of 40 nm Al Nanoparticles.

We present a remarkable improvement in the efficiency of AlGaN deep-ultraviolet light-emitting diodes (LEDs) enabled by the coupling of localized surface plasmon resonance (LSPR) mediated by a high-density array of Al nanoparticles (NPs). The Al NPs with an average diameter of ∼40 nm were uniformly distributed near the Al0.43Ga0.57N/Al0.50Ga0.50N multiple quantum well active region for coupling 285 nm emission by block copolymer lithography. The internal quantum efficiency is enhanced by 57.7% because of the decreased radiative recombination lifetime by the LSPR. As a consequence, the AlGaN LEDs with an array of Al NPs show 33.3% enhanced electroluminescence with comparable electrical properties to those of reference LEDs without Al NPs.

Perfect absorption in symmetrical single layer ultrathin metal grating with unilateral illumination

In symmetric environment, as the tangential electric field is almost constant across the ultrathin film, the absorption rate of the film is up to 0.5 under single side illumination. In this letter, we propose a symmetrical single layer ultrathin metal grating structure where perfect absorption (up to 0.99) can be achieved with unilateral illumination. We consider that this phenomenon of extraordinary optical absorption is caused by the coupling of the localized surface plasmon resonance and the long range surface plasmon. In particular, the electromagnetic response of the metal grating we proposed greatly resembles the electromagnetic induced absorption (EIA) which shows a narrow absorption peak within a broad absorption profile.

Multi-mode plasma resonator based on multi metal-coated nanorods

The surface plasmon resonance and strong coupling of three layers of metal-coated nanorods are studied in this paper. Numerical results show that an incident electromagnetic wave with a particular frequency can be guided through localized surface plasma resonances to different-sized cavities, realizing excellent absorbance of electromagnetic waves. The refractive index of the surrounding medium also influences the resonant frequency dramatically. Different metal shell thicknesses and materials can be used to effectively adjust the formant frequency. These unique properties of multi-mode resonance and excellent absorbance of electromagnetic waves in a multi-nanorod system have prospective applications in the fields of plasmon resonant sensors, resonators.

Quantum dot based mid-infrared photodetector enhanced by a hybrid metal-dielectric optical antenna

Surface plasmon waves and Rayleigh anomaly are characteristic optical phenomena exhibited by periodic subwavelength grating structures. In this paper, a hybrid metal-dielectric metasurface is proposed to improve the photoresponse of Ge/Si quantum dot infrared photodetectors (QDIPs) with limited absorption layer thickness. The composite metasurface consists of a regular array of silicon pillars. The pillars protrude through subwavelength holes in a perforated gold film on the detector top. We demonstrate that by combining effects of dielectric and plasmonic metal components, the QDIP photoresponse can be significantly improved compared to case when all-dielectric and metal gratings work alone. We observe about four times photoresponse enhancement with the hybrid metasurface device relative to a common plasmonic design with a two-dimensional metal hole array. Compared with a bare QDIP, the peak responsivity of the hybrid detector at a wavelength of 4.4 µm is increased by a factor of 15. The enhanced sensitivity is supposed to arise from coupling of the surface plasmon resonance and diffractive effect related to the Rayleigh anomaly.

Enhanced color sensitivity by coupling of surface plasmon and fabry-perot resonances for spectrometer-free and label-free biosensing

Plasmonic sensors have received much attention in recent years since they are highly sensitive to the refractive index changes of surrounding dielectric and can be applied to spectrometer-free biosensing. In particular, the sensing based on the color factors and the imaging is considered as a powerful method due to its simplified sensing process as well as high sensitivity with high spatial resolution. Herein, we report on improvement in the color sensitivity to the refractive index changes by employing an aluminum-silicon dioxide-aluminum (AOA) structure consisted of the Fabry-Perot (FP) cavity sandwiched between double surface plasmonic (SP) layers. The coupling of SP and FP resonances in aluminum nanohole arrays and silicon dioxide cavity lead to the synergistic or attenuated change in transmission spectra and colors. Therefore, as optimizing the coupling of the resonances to increase the color change, it is possible to obtain enhanced color sensitivity and more accurate refractive index prediction. Color sensitivities up to 122.29 (L*), 169.58 (a*), and 174.72 (b*) RIU−1 of the CIELAB color space are achieved through imaging process and statistical analysis. Uniform and sensitive sensing factors of AOA sensors can distinguish the concentration difference of bovine serum albumin (BSA) with a limit of detection of 9 × 10-4 RIU. Moreover, this approach confirms the possibility of being used for in vivo detection by observing the intracellular structure of HEK-293 cells. Our AOA sensor suggests a great potential to be utilized as a spectrometer-free, label-free, and functionalization-free detection of the refractive index and the transparent biomaterials.

Boosting Perovskite Photodetector Performance in NIR Using Plasmonic Bowtie Nanoantenna Arrays.

Triple-cation mixed metal halide perovskites are important optoelectronic materials due to their high photon to electron conversion efficiency, low exciton binding energy, and good thermal stability. However, the perovskites have low photon to electron conversion efficiency in near-infrared (NIR) due to their weak intrinsic absorption at longer wavelength, especially near the band edge and over the bandgap wavelength. A plasmonic functionalized perovskite photodetector (PD) is designed and fabricated in this study, in which the perovskite ((Cs0.06 FA0.79 MA0.15 )Pb(I0.85 Br0.15 )3 ) active materials are spin-coated on the surface of Au bowtie nanoantenna (BNA) arrays substrate. Under 785 nm laser illumination, near the bandedge of perovskite, the fabricated BNA-based plasmonic PD exhibits ≈2962% enhancement in the photoresponse over the Si/SiO2 -based normal PD. Moreover, the detectivity of the plasmonic PD has a value of 1.5 × 1012 with external quantum efficiency as high as 188.8%, more than 30 times over the normal PD. The strong boosting in the plasmonic PD performance is attributed to the enhanced electric field around BNA arrays through the coupling of localized surface plasmon resonance. The demonstrated BNA-perovskite design can also be used to enhance performance of other optoelectronic devices, and the concept can be extended to other spectral regions with different active materials.

In situ monitoring of silver adsorption on assembled gold nanorods by surface-enhanced Raman scattering

Self-assembly of metal nanocrystals is able to create a gap of sub-nanometer distance for concentrating incoming light by the strong coupling of surface plasmon resonance, known as a ‘hot spot’. Although the plasmonic property of silver is better than other metals in the visible range, the superior Raman enhancement of silver compared to gold is still under debate. To provide direct evidence, in this work, we studied the silver adsorption on assembled gold nanorods (AuNRs) using in situ surface-enhanced Raman scattering (SERS) measurements. The self-assembled AuNR multimers were used as the SERS substrate, where the 4-mercaptophenol (MPh) molecules in our experiment played dual roles as both probe molecules for the Raman scattering and linking molecules for the AuNR assembly in a basic environment. Silver atoms were adsorbed on the surface of gold nanorod assemblies by reduction of Ag+ anions. The stability of the adsorbed silver was guaranteed by the basic environment. We monitored the SERS signal during the silver adsorption with a home-built in situ Raman spectroscope, which was synchronized by recording the UV–vis absorption spectra of the reaction solution to instantly quantify the plasmonic effect of the silver adsorption. Although a minor change was found in the plasmonic resonance wavelength or intensity, the measured SERS signal at specific modes faced a sudden increase by 2.1 folds during the silver adsorption. The finite element method (FEM) simulation confirmed that the silver adsorption corresponding to the plasmonic resonance variation gave little change to the electric field enhancement. We attributed the mode-specific enhancement mechanism of the adsorption of silver to the chemical enhancement from charge transfer (CT) for targeting molecules with a specific orientation. Our findings provided new insights to construct SERS substrates with higher enhancement factor (EF), which hopefully would encourage new applications in the field of surface-enhanced optical spectroscopies.

Coupled plasmon resonances of Au thorn nanoparticles to enhance solar absorption performance

To enhance solar absorption performance of nanoparticles in the solar thermal conversion applications, the optical behavior of Au thorn nanoparticles is studied numerically. A new design strategy toward new nanostructures is provided by coupling with the local surface plasmon resonances and propagating surface plasmon resonances in this work. Results show that Au thorn nanoparticles have the broad absorption region compared with Au sphere nanoparticles due to the multi-resonance peaks. Further study reveals that the enhanced absorption mechanism of Au thorn nanoparticles can be attributed to the propagating surface plasmon resonances along the thorn part, which is coupled with the surface plasmon resonance of the bulk sphere part. Geometry parameters (radius, length, thorn number) are also investigated to tune optical properties of Au thorn nanoparticles. Finally, solar absorption efficiency calculation shows that Au thorn nanoparticles can achieve the higher solar absorption performance with less particle consumption than Au sphere nanoparticles.

Dynamically tunable excellent absorber based on plasmon-induced absorption in black phosphorus nanoribbon

The realization of plasmon-induced absorption (PIA) via local plasmon resonance coupling on the surface of two-dimensional metamaterials based on nanostructures heavily depends on the well-designed patterned antenna. However, due to the limitation of nanostructures’ size and the difficulty of material formation, it is challenging to achieve the expected performance of such a device. We propose and numerically simulate PIA in response to mid-infrared using two black phosphorus (BP) layers that are composed of upper double BP ribbons and lower single BP ribbons to avoid BP chips patterning. The theoretical transmission spectrum of the structure calculated by the coupled mode theory is in good agreement with the simulated curve. The resonant intensity of the reflection window is affected by interlayer spacing, and the resonant wavelength of the reflection window can be realized by dynamically varying carrier density. The absorption performance of the system can be enhanced not only by the gold mirror that is totally reflected at the bottom of the structure but also by the polarization angle of the incident wave. The designed system could be expected on various optical devices, including plasmonic sensors, dual-frequency absorbers, and switch controllers.

Target-Triggered Assembly of Nanogap Antennas to Enhance the Fluorescence of Single Molecules and Their Application in MicroRNA Detection.

Nanogap antennas are plasmonic nanostructures with a strong electromagnetic field generated at the gap region of two neighboring particles owing to the coupling of the collective surface plasmon resonance. They have great potential for improving the optical properties of fluorophores. Herein, nanogap antennas are constructed using an aqueous solution-based method to overcome the defects of weak fluorescence and photobleaching associated with traditional organic dyes, and a highly sensitive nanogap antenna-based sensing strategy is presented for the detection of low-abundance nucleic acid biomarkers via a target-triggered strand displacement amplification (SDA) reaction between two DNA hairpins that are tagged to the tips of gold nanorods (Au NRs). In the presence of targets, end-to-end Au NR dimers gradually form, and the fluorophores quenched by the Au NRs exhibit a dramatic fluorescence enhancement due to the plasmon-enhanced fluorescence effect of nanogap antennas. Meanwhile, the SDA reaction results in secondary amplification of fluorescence signals. Combined with single-molecule counting, this method applied in miRNA-21 detection can achieve a low detection limit of 97.2 × 10-18 m. Moreover, accurate discrimination between different cells through miRNA-21 imaging demonstrates the potential of this method in monitoring the expression level of low-abundance nucleic acid biomarkers.

Fano-Resonance in Hybrid Metal-Graphene Metamaterial and Its Application as Mid-Infrared Plasmonic Sensor.

Fano resonances in nanostructures have attracted widespread research interests in the past few years for their potential applications in sensing, switching and nonlinear optics. In this paper, a mid-infrared Fano resonance in a hybrid metal-graphene metamaterial is studied. The hybrid metamaterial consists of a metallic grid enclosing with graphene nanodisks. The Fano resonance arises from the coupling of graphene and metallic plasmonic resonances and it is sharper than plasmonic resonances in pure graphene nanostructures. The resonance strength can be enhanced by increasing the number of graphene layers. The proposed metamaterial can be employed as a high-performance mid-infrared plasmonic sensor with an unprecedented sensitivity of about 7.93 μm/RIU and figure of merit (FOM) of about 158.7.

Revealing Strong Plasmon-Exciton Coupling between Nanogap Resonators and Two-Dimensional Semiconductors at Ambient Conditions.

Strong coupling of two-dimensional semiconductor excitons with plasmonic resonators enables control of light-matter interaction at the subwavelength scale. Here we develop such strong coupling in plasmonic nanogap resonators, which allows modification of exciton strength by altering electromagnetic environments in nearby semiconductor monolayers. Using this system, we not only demonstrate a large vacuum Rabi splitting up to 163meV and splitting features in photoluminescence spectra but also reveal that the effective exciton number contributing to the coupling can be reduced down to the single-digit level (N<10), which is 2 orders lower than that of previous systems, close to single-exciton based strong coupling. In addition, we prove that the strong coupling process is not affected by the large exciton coherence size that was previously believed to be detrimental to the formation of plasmon-exciton interaction. We provide a deeper understanding of strong coupling in two-dimensional semiconductors, paving the way for room-temperature quantum optics applications.

Silver nanoparticles enhanced luminescence and stability of CsPbBr3 perovskite quantum dots in borosilicate glass

AbstractSeries of silver nanoparticles (NPs) embedded CsPbBr3 quantum dots (QDs) glass was synthesized via the melt‐quench method. Ag NPs and CsPbBr3 QDs coexist in the TEM image of the Ag‐doped glass sample. Photoluminescence (PL) spectra show that the 0.1 molar ratio Ag2O‐doped sample had a PL intensity 2.37 times than the undoped sample. This increase is generated by localized surface plasmon resonance coupling between the Ag NPs and CsPbBr3 QDs. Excessive Ag doping weakens the PL intensity due to spectral self‐absorption of the Ag NP surface plasmon resonance (SPR). Self‐adsorption of SPR is detrimental to luminescence properties because it increases the amount of photogenerated charge carriers, which proceed through nonradiative relaxation pathways. In addition, stability results of Ag NP‐doped‐CsPbBr3 QD glass show that they have excellent stability. This study on Ag NP‐doped‐CsPbBr3 QD glass provides a new idea for the future development of perovskite QD optoelectronic devices.

Controlled growth of Cu2−xS sheet-like nanoshells and Cu2−xS–CdS p–n junctions on Au nanorods with coupled plasmon resonances and enhanced photocatalytic activities

Controlled growth of Cu2−xS sheet-like nanoshells and Cu2−xS–CdS p–n junctions on Au nanorods with enhanced photocatalytic activity.

Utilizing molecular resonance-localized surface plasmon resonance coupling for copper ion detection in plasma.

The rapid, point-of-care detection of copper in plasma can greatly aid in a large number of diseases where copper has been implicated to be an important factor, such as cancer, Alzheimer's and Diabetes mellitus. Localized surface plasmon resonance (LSPR) technologies show promise in the inexpensive detection of copper, whereas previous platforms are plagued with selectivity and sensitivity issues. Herein, we have created a sensitive and selective on-chip copper sensor which can produce a colorimetric reading in 60 minutes. The selectivity of the assay is based on 'Click' chemistry and is shown to have little interference with other metal ions present in plasma. The sensitivity of the assay is generated from the coupling of the molecular resonance of a dye and the LSPR of the gold nanoparticles. The assay is capable of measuring copper concentrations in human plasma as low as 4 μM and the linear range of sensitivity, 4 to 20 μM, is in the physiologically relevant range. This robust, colorimetric assay should prove useful in a point-of-care setting.

Synergistic plasmon resonance coupling and light capture in ordered nanoarrays as ultrasensitive and reproducible SERS substrates.

An effective SERS substrate for on-field detection needs to satisfy high sensitivity to analyte and signal reproducibility even in the special case of tilting or bending of substrates. Herein, we transferred monolayer AuNPs into a nanocavity to construct a Au particle-in-hemispherical honeycomb nanoarray (PIHHN) as an ultrasensitive and spatially reproducible SERS substrate. The capacity of detection for R6G in an optimal PIHHN substrate is as low as a concentration of 10-15 M, and the RSD of signal deviation is no more than 5.6%. FDTD simulations explain that placing AuNPs into a metallic nanocavity can capture and focus the light field to improve the interaction between the light and the substrate and provide the collective effect of multiple plasmon coupling, which can induce a stronger electromagnetic field. In addition, the system can generate more hot spots between AuNPs and between AuNPs and the metallic nanocavity. In particular, when the substrate is tilted or bent at an angle from 0° to 60°, the SERS performance remains stable due to the rotational symmetry of the PIHHN structure, which demonstrates the capability of on-field detection. Furthermore, the PIHHN substrate is employed as a highly sensitive multiplex sensor in on-field analysis for contaminated soil, achieving the detection of analytes down to 0.5 ppb.

High-Performance Nano-Sensing and Slow-Light Applications Based on Tunable Multiple Fano Resonances and EIT-Like Effects in Coupled Plasmonic Resonator System

A basic plasmonic system, consisting of a stub metal-insulator-metal (MIM) waveguide coupled with a ring resonator, is presented to realize Fano resonance and electromagnetically induced transparency-like (EIT-like) effect, which are numerically calculated by the finite element method (FEM). Meanwhile, the formation mechanism of Fano resonance is analyzed according to numerical simulations. Besides, the coupled mode theory (CMT) and the standing wave theory are used for explaining the Fano and EIT-like resonances phenomenon. Based on this system, an inner ring cavity is connected to the ring resonator by a slot and another ring cavity is later introduced under the stub resonator in order to constitute a new coupled plasmonic resonator system, providing quadruple Fano resonances and double EIT-like responses finally. In addition, the Fano and EIT-like resonances can be independently tuned by adjusting the structural parameters, which makes the design of highly integrated photonic circuits more flexible. The main contribution of this paper is that the proposed structure has a relatively good sensitivity of 1600 nm/RIU and an ultra-high FOM value of $1.2\times 10^{6}$ as a refractive index nanosensor. Moreover, it can serve as an all-optical switch with a high on/off extinction ratio of about 43 dB. Additionally, its maximum group delay time and group index are about 1.49 ps and 221, indicating that the proposed system has a pretty good slow light effect. Therefore, the proposed structures are believed to have significant applications in high-performance nanosensors, switches, slow light devices and nonlinear areas in highly integrated plasmonic devices.

TiO2 inverse opal structures with facile decoration of precious metal nanoparticles for enhanced photocatalytic activity

TiO2 inverse opal (IO) structures were fabricated by an infiltration method that were functionalized with gold, silver, and gold-silver core-shell metal nanoparticles. The photocatalytic activity of the TiO2 IO structures with metal nanoparticles was characterized by gas-phase conversion of acetylene into carbon dioxide. All metal nanoparticle functionalized structures showed an increase in photocatalytic activity via surface plasmon resonance coupling of the incident light. The highest photocatalytic activity was observed with gold-silver core-shell nanoparticle functionalized TiO2 IO structure (increase of 62% compared to reference TiO2 IO) followed by gold (53%) and silver (39%) nanoparticles.