Advances in surface plasmon resonance for analyzing active components in traditional Chinese medicine

The surface plasmon resonance(SPR)biosensor technology is a novel optical analysis method for studying intermolecular interactions.Owing to in-depth research on traditional Chinese medicine(TCM)in recent years,comprehensive and specific identification of components and target interactions has become key yet difficult tasks.SPR has gradually been used to analyze the active components of TCM owing to its high sensitivity,strong exclusivity,large flux,and real-time monitoring capabilities.This review sought to briefly introduce the active components of TCM and the principle of SPR,and provide historical and new insights into the application of SPR in the analysis of the active components of TCM.

An externally perceivable smart leaky-wave antenna based on spoof surface plasmon polaritons

Smart antennas have received great attention for their potentials to enable communication and perception functions at the same time.However,realizing the function synthesis remains an open challenge,and most existing system solutions are limited to narrow operating bands and high complexity and cost.Here,we propose an externally perceivable leakywave antenna(LWA)based on spoof surface plasmon polaritons(SSPPs),which can realize adaptive real-time switching between the“radiating”and“non-radiating”states and beam tracking at different frequencies.With the assistance of computer vision,the smart SSPP-LWA is able to detect the external target user or jammer,and intelligently track the target by self-adjusting the operating frequency.The proposed scheme helps to reduce the power consumption through dynamically controlling the radiating state of the antenna,and improve spectrum utilization and avoid spectrum conflicts through intelligently deciding the radiating frequency.On the other hand,it is also helpful for the physical layer communication security through switching the antenna working state according to the presence of the target and target beam tracking in real time.In addition,the proposed smart antenna can be generalized to other metamaterial systems and could be a candidate for synaesthesia integration in future smart antenna systems.

Reconfigurable exceptional point-based sensing with 0.001λsensitivity using spoof localized surface plasmons

Recent breakthroughs in the field of non-Hermitian physics present unprecedented opportunities,from fundamental theories to cutting-edge applications such as multimode lasers,unconventional wave transport,and high-performance sensors.The exceptional point,a spectral singularity widely existing in non-Hermitian systems,provides an indispensable route to enhance the sensitivity of optical detection.However,the exceptional point of the forementioned systems is set once the system is built or fabricated,and machining errors make it hard to reach such a state precisely.To this end,we develop a highly tunable and reconfigurable exceptional point system,i.e.,a single spoof plasmonic resonator suspended above a substrate and coupled with two freestanding Rayleigh scatterers.Our design offers great flexibility to control exceptional point states,enabling us to dynamically reconfigure the exceptional point formed by various multipolar modes across a broadband frequency range.Specifically,we experimentally implement five distinct exceptional points by precisely manipulating the positions of two movable Rayleigh scatterers.In addition,the enhanced perturbation strength offers remarkable sensitivity enhancement for detecting deep-subwavelength particles with the minimum dimension down to 0.001λ(withλto be the free-space wavelength).

Surface plasmon resonance-induced visible-light photocatalytic performance of silver/silver molybdate composites

Novel silver/silver molybdate（Ag/Ag2MoO4） composites with surface plasmon resonance（SPR）-enhanced photocatalytic performance were successfully fabricated via a facile one-pot hydrothermal route with the presence of sodium dodecyl sulfate（SDS） in this study.The as prepared silver/silver molybdate（Ag/Ag2MoO4） composites were systematically characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM） and ultraviolet-visible diffuse reflectance absorption spectroscopy（DRS） in order to investigate their crystal structure,morphology and optical property as well.The photocatalytic activities of the composites were subsequently evaluated by their ability to degrade rhodamine B（RhB） under visible-light irradiation.Varies of controlled experiments were then carefully operated to gain a deep insight into the assembling of Ag/Ag2MoO4composites.It was found that preparation conditions such as pH,reaction time,and the amount of surfactant played important roles in the formation of composites with octahedral microstructures.And the composite obtained at 160 ℃ using 0.5 g of sodium dodecyl sulfate exhibited the highest photocatalytic performance under visible-light irradiation.Capture experiments were also conducted to clarify the function of different active species generated on the surface of Ag/Ag2MoO4during the photocatalytic process,in which both holes and ·OH radicals were found to play crucial role in photocatalytic removal of RhB under visible light irradiation.A possible photocatalytic mechanism of Ag/Ag2MoO4 was finally proposed on the basis of all the results to explain the higher photocatalytic activity of the octahedral Ag/Ag2MoO4 composites.It was inferred that the photoinduced ＂hot＂ electrons can quickly transfer from the Ag NPs to the conduction band of Ag2MoO4 and react with oxygen and H2O to generate a large quality of active radicals such as ·OH and ·O2^- because of the SPR effects.Besides,this SPR effects of Ag nanoparticles deposited on the surface of Ag2MoO4 can not only dramatically amplify its light absorption,especially in the visible region,but also promote the separation of photoexcited electron-hole pairs and effectively decrease electron-hole recombination.

Investigation on Surface Plasmon Polaritons and Localized Surface Plasmon Production Mechanism in Micro-Nano Structures

The simulation mechanism of surface plasmon polaritons(SPPs)and localized surface plasmon(LSP)in different structures was studied,including the Au reflection grating(Au grating),Au substrate with dielectric ribbons grating(Au substrate grating),and pure electric conductor(PEC)substrate with Au ribbons grating(Au ribbons grating).And the characteristics of the Smith-Purcell radiation in these structures were presented.Simulation results show that SPPs are excited on the bottom surface of Au substrate grating grooves and LSP is stimulated on the upper surface both of Au ribbons grating grooves and Au grating grooves.Owing to the irreconcilable contradiction between optimizing the grating diffraction radiation efficiency and optimizing the SPPs excitation efficiency in the Au substrate grating,only 40-times enhancement of the radiation intensity was obtained by excited SPPs.However,the LSP enhanced structure overcomes the above problem and gains much better radiation enhancement ability,with about 200-times enhancement obtained in the Au ribbons grating and more than 500-times enhancement obtained in the Au grating.The results presented here provide a way of developing miniature,integratable,tunable,high-power-density radiation sources from visible light to ultraviolet rays at room temperature.

Surface plasmon polaritons frequency-blue shift in low confinement factor excitation region

Surface plasmon polaritons'(SPPs')frequency blue shift is observed in finite-difference time-domain(FDTD)simulation of parallel electron excitation Au bulk structure.Comparing with cold dispersion of SPPs,an obvious frequency blue shift is obtained in low confinement region excitation simulation results.Then,according to SPPs'transverse attenuation characteristics,the excited frequency mode instead of cold dispersion corresponding frequency mode matches it.Thence,this excited mode is confirmed to be SPPs'mode.As is well known the lower the frequency,the smaller the confinement factor is and the lower the excitation efficiency,the wider the bandwidth of excited SPPs is.And considering the attenuation in whole structure,the excited surface field contains attenuation signal.In a low confinement factor region,the higher the SPPs'frequency,the higher the excitation efficiency is,while broadband frequency information obtained in attenuation signal provides high frequency information in stimulation signal.Thence,in the beam-wave interaction,as the signal oscillation time increases,the frequency of the oscillation field gradually increases.Thus,compared with cold dispersion,the frequency of excited SPP is blueshifted This hypothesis is verified by monitoring the time domain signal of excited field in low and high confinement factor regions and comparing them.Then,this frequency-blue shift is confirmed to have commonality of SPPs,which is independent of SPPs'material and structure.Finally,this frequency-blue shift is confirmed in an attenuated total reflection(ATR)experiment.Owing to frequency dependence of most of SPPs'devices,such as coherent enhancement radiation and enhancement transmission devices,the frequency-blue shift presented here is of great influence in the SPPs applications.

Numerical investigation of the enhanced unidirectional surface plasmon polaritons generator

A unidirectional surface plasmon polaritons(SPPs) generator with greatly enhanced generation efficiency is proposed. The SPPs generator consists of an asymmetric single nanoslit coated with a polyviny alcohol(PVA) film and a silver rectangle block. The generation efficiency of this SPPs generator is investigated using the finite difference time domain method. Due to the presence of the silver rectangle block, the SPPs generation efficiency of the asymmetric single nanoslit with PVA film can be greatly enhanced and the corresponding wavelength with the maximum enhancement factor can be tuned flexibly. The influence of the structural parameters on the generation efficiency is also investigated for the enhanced unidirectional SPPs generator.

Surface Plasmon Resonance Sensors Based on Polymer Optical Fiber

Surface Plasmon Resonance （SPR） is a powerful technique for directly sensing in biological studies, chemical detection and environmental pollution monitoring. In this paper, we present polymer optical fiber application in SPR sensors, including wavelength interrogation surface enhanced Raman scattering SPR sensor and surface enhanced Raman scattering （SERS） probe. Long-period fiber gratings are fabricated on single mode polymer optical fiber （POF） with 120 μm period and 50% duty cycle. The polarization characteristic of this kind of birefringent grating is studied. Theoretical analysis shows it will be advantageous in SPR sensing applications.

Using a Surface Plasmon Resonance Biosensor for Rapid Detection of Salmonella Typhimurium in Chicken Carcass

Chicken is one of the most popular meat products in the world. Salmonella Typhimurium is a common foodbome pathogens associated with the processing of poultry. An optical Surface Plasmon Resonance （SPR） biosensor was sensitive to the presence of Salmonella Typhimurium in chicken carcass. The Spreeta biosensor kits were used to detect Salmonella Typhimurium on chicken carcass successfully. A taste sensor like electronic tongue or biosensors was used to basically ＂taste＂ the object and differentiated one object from the other with different taste sensor signatures. The surface plasmon resonance biosensor has potential for use in rapid, real-time detection and identification of bacteria, and to study the interaction of organisms with dif- ferent antisera or other molecular species. The selectivity of the SPR biosensor was assayed using a series of antibody con- centrations and dilution series of the organism. The SPR biosensor showed promising to detect the existence of Salmonella Typhimurium at 1 x 106 CFU/ml. Initial results show that the SPR biosensor has the potential for its application in pathogenic bacteria monitoring. However, more tests need to be done to confirm the detection limitation.

Surface Plasmon Assisted Directional Rayleigh Scattering

The origin of the Rayleigh scattering ring effect has been experimentally examined on a quantum dot/metal film system, in which CdTe quantum dots embedded in PVP are spincoated on a thin Au film. On the basis of the angle-dependent, optical measurements under different excitation schemes （i.e., wavelength and polarization）, we demonstrate that surface plasmon assisted directional radiation is responsible for such an effect. Moreover, an interesting phase-shift behavior is addressed.

Analysis of 17β-Estadiol from Sewage in Coastal Marine Environment by Surface Plasmon Resonance Technique

In this study, surface plasmon resonance （SPR） for monitoring 17β-eatradiol （E2） was developed. The small molecule E2 was immobilized on a CM5 sensor chip for an indirect competitive immunoassay to detect E2. The SPR response bahed on the antigen-antibody reaction was measured by injecting the sample solution into the flow system. The limitation of detection was 0.445 μg/L. The developed SPE-SPR system was applied to analyze the seawater samples. Recovery of E2 was 91.6%-93. 1%. Relative standard deviations（RSD） for the E2 assay were between 10.9%-15.1% （n = 3）. The range of determination of E2 samples from the sewage in the coastal marine environ-ment was between ND（lower than detection limit） and ca. 11.78 ng/L.

A strategy of screening and binding analysis of bioactive components from traditional Chinese medicine based on surface plasmon resonance biosensor

Elucidating the active components of traditional Chinese medicine(TCM)is essential for understanding the mechanisms of TCM and promote its rational use as well as TCM-derived drug development.Recent studies have shown that surface plasmon resonance(SPR)technology is promising in this field.In the present study,we propose an SPR-based integrated strategy to screen and analyze the major active components of TCM.We used Radix Paeoniae Alba(RPA)as an example to identify the compounds that can account for its anti-inflammatory mechanism via tumor necrosis factor receptor type 1(TNF-R1).First,RPA extraction was analyzed using an SPR-based screening system,and the potential active ingredients were collected,enriched,and identified as paeoniflorin and paeonol.Next,the affinity constants of paeoniflorin and paeonol were determined as 4.9 and 11.8 mM,respectively.Then,SPR-based competition assays and molecular docking were performed to show that the two compounds could compete with tumor necrosis factor-a(TNF-a)while binding to the subdomain 1 site of TNF-R1.Finally,in biological assays,the two compounds suppressed cytotoxicity and apoptosis induced by TNF-a in the L929 cell line.These findings prove that SPR technology is a useful tool for determining the active ingredients of TCM at the molecular level and can be used in various aspects of drug development.The SPR-based integrated strategy is reliable and feasible in TCM studies and will shed light on the elucidation of the pharmacological mechanism of TCM and facilitate its modernization.

The theoretic analysis of maskless surface plasmon resonant interference lithography by prism coupling

The use of an attenuated total reflection-coupling mode of prism coated with metal film to excite the interference of the surface plasmon polaritons （SPPs） was proposed for periodic patterning with a resolution of subwavelength scale. High intensity of electric field can be obtained because of the coupling between SPPs and evanescence under a resonance condition, which can reduce exposure time and improve contrast. In this paper, several critical parameters for maskless surface plasmon resonant lithography are described, and the preliminary simulation based on a finite difference timedomain technique agrees well with the theoretical analysis, which demonstrates this scheme and provides the theoretical basis for further experiments.

Surface plasmon resonance analysis to evaluate the importance of heparin sulfate groups＇ binding with human aFGF and bFGF

Human acidic and basic fibroblast growth factors (aFGF and bFGF) are classic and well characterized members of the heparin binding growth factor family. Heparin is generally thought to play an extremely important role in regulating aFGF and bFGF bioactivities through its strong binding with them. In order to unravel the mechanism of the interactions between heparin and FGFs, and evaluate the importance of heparin sulfate groups' binding with FGFs, surface plasmon resonance analyses were performed using IAsys Cuvettes System. Heparin and its regioselectively desulfated derivatives were immobilized on the cuvettes. aFGF and bFGF solutions with different concentrations were pipetted into the cuvettes and the progress of the interaction was monitored in real\|time by Windows based software, yielding kinetic and equilibrium constants for these interactions. In addition, in order to reduce the delicate difference among the cuvettes, inhibition analyses of mixture of FGFs and immobilized native heparin by modified heparins were also done. The data from these two methods were similar, indicating that all sulfate groups at 2 O, 6 O and N in heparin were required for the binding to aFGF; and that their contribution to the binding was in the order 2 O, N and 6 O sulfate group. In contrast, definite contribution of the 6 O sulfate group to the binding with bFGF was most apparent, while the other two sulfate groups appeared to be necessary in the order 2 O and N sulfate group. These methods established here can be used for analysing the effect of sulfate groups in heparin on the binding with other human FGF members or other heparin binding proteins.

Ultrasensitive nanosensors based on localized surface plasmon resonances:From theory to applications

The subwavelength confinement feature of localized surface plasmon resonance（LSPR） allows plasmonic nanostructures to be functionalized as powerful platforms for detecting various molecular analytes as well as weak processes with nanoscale spatial resolution. One of the main goals of this field of research is to lower the absolute limit-of-detection（LOD）of LSPR-based sensors. This involves the improvement of（i） the figure-of-merit associated with structural parameters such as the size, shape and interparticle arrangement and,（ii） the spectral resolution. The latter involves advanced target identification and noise reduction techniques. By highlighting the strategies for improving the LOD, this review introduces the fundamental principles and recent progress of LSPR sensing based on different schemes including 1） refractometric sensing realized by observing target-induced refractive index changes, 2） plasmon rulers based on target-induced relative displacement of coupled plasmonic structures, 3） other relevant LSPR-based sensing schemes including chiral plasmonics,nanoparticle growth, and optomechanics. The ultimate LOD and the future trends of these LSPR-based sensing are also discussed.

Surface plasmon polariton and mode transformation in a nanoscale lossy metallic cylindrical cable

A theoretical investigation on the surface plasmon polariton in a gold cylindrical nanocable is presented. By solving a complete set of Maxwell＇s equations in the nanocable （with a 50 nm radius gold nanocore, 10-300 nm silica layer, and 30-200nm gold nanocladding）, the dispersion relations on the optical frequency and on the silica thickness are discussed. When the silica thickness varies from 50 to 250 nm, at a fixed waveleltgth, the strong coupling between the gold nanocore and the nanocladding leads to a symmetric-like surface mode and an antisymmetric-like surface mode in the nanocable. The transformation between the surface mode and the waveguide mode in this structure is also investigated. The results will be helpful for understanding the surface waves in the subwavelength structures.

Tunable localized surface plasmon resonances in MoO_(3-x)-TiO_(2) nanocomposites with enhanced catalytic activity for CO_(2) photoreduction under visible light

The photocatalytic reduction of CO2 with H2O to fuels and chemicals using solar energy is one of the most attractive but highly difficult routes.Thus far,only a very limited number of photocatalysts has been reported to be capable of catalyzing the photocatalytic reduction of CO2 under visible light.The utilization of the localized surface plasmon resonance(LSPR)phenomenon is an attractive strategy for developing visible-light photocatalysts.Herein,we have succeeded in synthesizing plasmonic MoO3?x-TiO2 nanocomposites with tunable LSPR by a simple solvothermal method.The well-structured nanocomposite containing two-dimensional(2D)molybdenum oxide(MoO3?x)nanosheets and one-dimensional(1D)titanium oxide nanotubes(TiO2-NT)showed LSPR absorption band in the visible-light region,and the incorporation of TiO2-NT significantly enhanced the LSPR absorption band.The MoO3?x-TiO2-NT nanocomposite is promising for application in the photocatalytic reduction of CO2 with H2O under visible light irradiation.

Review of improved spectral response of ultraviolet photodetectors by surface plasmon

Ultraviolet(UV) photodetectors based on wide band gap semiconductor have attracted much attention for their small volume, low working voltage, long lifetime, good chemical and thermal stability. Up to now, many researches have been done on the semiconductors based UV detectors and some kinds of detectors have been made, such as metal–semiconductor–metal(MSM), Schottky, and PIN-type detectors. However, the sensitivity values of those detectors are still far from the expectation. Recent years, surface plasmon(SP) has been considered to be an effective way to enhance the sensitivity of semiconductor based UV photodetector. When the light is matched with the resonance frequency of surface plasmon, the localized field enhancement or scattering effect will happen and thus the spectral response will be enhanced.Here, we present an overview of surface plasmon enhancing the performance of UV detectors, including the GaN, ZnO,and other wide band gap semiconductor UV detectors. Both fundamental and experimental achievements are contained in this review.

Coherent and tunable radiation with power enhancement from surface plasmon polaritons

Surface plasmon polaritons excited by an electron beam can be transformed into coherent and tunable light radiation waves with power enhancement in the simple structure of a metal film with a dielectric medium loading. In this paper, the process of the radiation transformation of this radiation, and the dependencies of the radiation characteristics on the parameters of the structure and the electron beam are studied in detail. The radiation power enhancement is greatly influenced by the beam energy and the film thickness in the infrared to ultraviolet frequency region. Up to 122 times radiation power enhancement and 6.5% radiation frequency tuning band can be obtained by optimizing the beam energy and the parameters of the film.

Surface plasmon-enhanced dual-band infrared absorber for VO_x-based microbolometer application

We propose a periodic structure as an extra absorption layer（i.e., absorber） based on surface plasmon resonance effects, enhancing dual-band absorption in both middle wavelength infrared（MWIR） and long wavelength infrared（LWIR）regions. Periodic gold disks are selectively patterned onto the top layer of suspended SiN/VO_2/SiN sandwich-structure.We employ the finite element method to model this structure in COMSOL Multiphysics including a proposed method of modulating the absorption peak. Simulation results show that the absorber has two absorption peaks at wavelengths λ =4.8 μm and λ = 9 μm with the absorption magnitudes more than 0.98 and 0.94 in MWIR and LWIR regions, respectively. In addition, the absorber achieves broad spectrum absorption in LWIR region, in the meanwhile, tunable dual-band absorption peaks can be achieved by variable heights of cavity as well as diameters and periodicity of disk. Thus, this designed absorber can be a good candidate for enhancing the performance of dual band uncooled infrared detector, furthermore, the manufacturing process of cavity can be easily simplified so that the reliability of such devices can be improved.