A broadband cross-polarization conversion anisotropic metasurface based on multiple plasmon resonances

A compact broadband cross-polarization conversion metasurface functioning in the microwave regime is realized and experimentally demonstrated. The metasurface consists of a two-dimensional periodic arrangement of anisotropic double- slit split-ring-resonator-based unit cells printed on top of a dielectric substrate, backed by metallic cladding. The proposed metasurface converts an x- or y-polarized wave into its orthogonal polarization over a fractional bandwidth of 100% from 5- 15 GHz, both for normal as well as oblique incidence. Moreover, the sub-wavelength unit-cell size, thin dielectric substrate, and unique unit-cell design collectively make the response of the metasurface same for both polarizations and insensitive to the incidence angle. The designed structure is fabricated and tested. The measurement and simulation results are found to be consistent with each other.

High-order plasmon resonances in an Ag/Al_2O_3 core/shell nanorice

Using numerical simulation, we investigate the high-order plasmon resonances in individual nanostructures of an Ag nanorice core surrounded by an Al2O3 shell. The peak positions of localized surface plasmon resonances （LSPRs） are red-shifted exponentially with the increase of the dielectric shell thickness. This is due to the exponential decay of electromagnetic field intensity in the direction perpendicular to the interface. This exponential red-shift depends on the wavelength of the resonance peak instead of the resonance order. In addition, we find that the LSPRs in an Ag nanorice of 60-nm width can be perfectly described by a single linear function. These features make nanorice an ideal platform for sensing applications.

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.

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.

Manipulated localized surface plasmon resonances in silver nanoshells coated with a spherical anisotropic layer

The influences of the anisotropy of the outer spherically anisotropic （SA） layer on the far-field spectra and near- field enhancements of the silver nanoshells are investigated by using a modified Mie scattering theory. It is found that with the increase of the anisotropic value of the SA layer, the dipole resonance wavelength of the silver nanoshell first increases and then decreases, while the local field factor （LFF） reduces. With the decrease of SA layer thickness, the dipole wavelength of the silver nanoshell shows a distinct blue-shift. When the SA layer becomes very thin, the modulations of the anisotropy of the SA layer on the plasmon resonance energy and the near-field enhancement are weakened. We further find that the smaller anisotropic value of the SA layer is helpful for obtaining the larger near-field enhancement in the Ag nanoshell. The geometric average of the dielectric components of the SA layer has a stronger effect on the plasmon resonance energy of the silver nanoshell than on the near-field enhancement.

Tunable multiple plasmon resonances and local field enhancement of nanocrescent/nanoring structure

According to the plasmon hybridization theory, the plasmon resonance characteristics of the gold nanocrescent/nanoring(NCNR) structure are systematically investigated by the finite element method. It is found that the extinction spectra of NCNR structure exhibit multiple plasmon resonance peaks, which could be attributed to the result of the plasmon couplings between the multipolar plasmon modes of nanocrescent and the dipolar, quadrupolar, hexapolar, octupolar,decapolar plasmon modes of nanoring. By changing the geometric parameters, the intense and separate multiple plasmon resonance peaks are obtained and can be tuned in a wide wavelength range. It is further found that the plasmon coupling induces giant multipole electric field enhancements around the tips of the nanocrescent. The tunable and intense multiple plasmon resonances of NCNR structure may provide effective applications in multiplex biological sensing.

A time-dependent density functional theory investigation of plasmon resonances of linear Au atomic chains

We report theoretical studies on the plasmon resonances in linear Au atomic chains by using ab initio time- dependent density functional theory. The dipole responses are investigated each as a function of chain length. They converge into a single resonance in the longitudinal mode but split into two transverse modes. As the chain length increases, the longitudinal plasmon mode is redshifted in energy while the transverse modes shift in the opposite direction （blueshifts）. In addition, the energy gap between the two transverse modes reduces with chain length increasing. We find that there are unique characteristics, different from those of other metallic chains. These characteristics are crucial to atomic-scale engineering of single-molecule sensing, optical spectroscopy, and so on.

Photothermal properties of Cu@polycarbonate composites with strong localized surface plasmon resonances

Copper is relatively low cost and highly abundant compared with the well-studied noble metals such as gold and silver.However,the poor plasmonic and high susceptibility towards oxidation limit the study of its optical properties and applications as well.Herein,copper nanoparticles@polycarbonate(Cu@PC)composites were prepared by using a facile one-step solvothermal method.The Cu@PC composites have strong localized surface plasmon resonances(LSPR)due to that the PC shell can induce the particles to form many-particles system with different particle numbers,which not only lead to overlap and hybridize of the LSPR modes,but also shift the LSPR away from the interband transitions,and the PC layer also prevents the oxidation of Cu nanoparticles.The photothermal conversion efficiency of Cu@PC composites reaches 41.1%under 808 nm continuous wave(CW)laser irradiation which is higher than previously reported Cu nanomaterials that have been reported.Meanwhile,the composites also have high photothermal stability.Moreover,interfacial evaporator is prepared by assembling the Cu@PC composites on scouring sponge as light absorption layer which has>92.8%absorption in entire solar spectrum range.Its seawater evaporation rate is 3.177 kg·m^(-2)·h^(-1)with a E_(evaporator)/E_(water)of 5.2.The high evaporation rate interfacial evaporator with low cost,simple,and scalable approach shows great application value in the field of photothermal evaporation.

Design and applications of lattice plasmon resonances

With their unique optical properties associated with the excitation of surface plasmons, metal nanoparticles （NPs） have been used in optical sensors and devices. The organization of these NPs into arrays can induce coupling effects to engineer new optical responses. In particular, lattice plasmon resonances （LPRs）, which arise from coherent interactions and coupling among NPs in periodic arrays, have shown great promise for realizing narrow linewidths, angle-dependent dispersions, and high wavelength tunability of optical spectra. By engineering the materials, shapes, sizes, and spatial arrangements of NPs within arrays, one can tune the LPR-based spectral responses and electromagnetic field distributions to deliver a multitude of improvements, including a high figure-of-merit, superior light-matter interaction, and multiband operation. In this review, we discuss recent progress in designing and applying new metal nanostructures for LPR-based applications. We conclude this review with our perspective on the future opportunities and challenges of LPR-based devices.

Refractive Plasmonic Sensor Based on Fano Resonances in an Optical System

A symmetric plasmonie structure consisting of metal-insulator metal waveguide, groove studied, which supports double Fano resonances deriving from two different mechanisms and slot cavities is One of the Fano resonances originates from the interference between the resonances of groove and slot cavities, and the other comes from the interference between slot cavities. The spectral line shapes and the peaks of the double Fano resonances can be modulated by changing the length of the slot cavities and the height of the groove. Furthermore, the wavelength of the resonance peak has a linear relationship with the length of the slot cavities. The proposed plasmonic nanosensor possesses a sensitivity of 800nm/RIU and a figure of merit of 3150, which may have important applications in switches, sensors, and nonlinear devices.

Polarization-Insensitive Magnetic Quadrupole-Shaped and Electric Quadrupole-Shaped Fano Resonances Based on a Plasmonic Composite Structure

A combined structure with the unit cell consisting of four sub-units with 90° rotation in turn is designed. Each of sub-units is composed of two gold rods in transverse arrangement and one gold rod in longitudinal arrangement. Simulating electromagnetic responses of the structure, we verify that the structure exhibits the double Fano resonances, which originate from the coupling between magnetic quadrupoles and electric dipoles and the coupling between electric quadrupoles and electric dipoles. Simulation results also demonstrate that the structure is polarization-insensitive and shows an analogue of electromagnetically induced transparency at the two Fano resonances. Such a plasmonic structure has potential applications in photoelectric elements.

Rapid and fine tailoring longitudinal surface plasmon resonances of gold nanorods by end-selective oxidation

Facile achievement of gold nanorods(AuNRs) with controllable longitudinal surface plasmon resonance(LSPR) is of great importance for their applications in various fields.The LSPR of AuNRs is sensitive to their aspect ratio,which is still hard to be precisely tuned by direct synthesis.In this work,we report a simple approach for end-selective etching of AuNRs by a rapid oxidation process with Au(Ⅲ) in cetyltrimethylammonium bromide(CTAB) solution at a mild temperature.The LSPR wavelength and the length of AuNRs blue shifted linearly as a function of the amount of Au(Ⅲ),while the diameter of Au NRs remained nearly constant.The oxidative rate is tempe rature dependent,and the oxidative process for a desired LSPR can be accomplished within 15 min at 60℃.Further investigations indicated that Br determine the occurrence of the oxidation between AuNRs and Au(Ⅲ),and a small amount of surfactant chain(CTA+) is crucial for stabilizing AuNRs.This method presents a quick but robust strategy for acquiring AuNRs with an arbitrary intermediate LSPR wavelength using the same starting AuNRs,and can be a powerful tool for subsequent applications.

Nitrogen-doped microporous graphite-enhanced copper plasmonic effect for solar evaporation

Water scarcity is a global challenge,and solar evaporation technology offers a promising and eco-friendly solution for freshwater production.Photothermal conversion materials(PCMs)are crucial for solar evaporation.Improving photothermal conversion efficiency and reducing water evaporation enthalpy are the two key strategies for the designing of PCMs.The desired PCMs that combine both of these properties remain a challenging task,even with the latest advancements in the field.Herein,we developed copper nanoparticles(NPs)with different conjugated nitrogen-doped microporous carbon coatings(Cu@C–N)as PCMs.The microporous carbon enveloping layer provides a highly efficient pathway for water transport and a nanoconfined environment that protects Cu NPs and facilitates the evaporation of water clusters,reducing the enthalpy of water evaporation.Meanwhile,the conjugated nitrogen nodes form strong metal-organic coordination bonds with the surface of copper NPs,acting as an energy bridge to achieve rapid energy transfer and provide high solar-to-vapor conversion efficiency.The Cu@C–N exhibited up to 89.4%solar-to-vapor conversion efficiency and an evaporation rate of 1.94 kgm^(−2) h^(−1) under one sun irradiation,outperforming conventional PCMs,including carbon-based materials and semiconductor materials.These findings offer an efficient design scheme for high-performance PCMs essential for solar evaporators to address global water scarcity.

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.

Photocatalytic seawater splitting by 2D heterostructure of ZnIn_(2)S_(4)/WO_(3) decorated with plasmonic Au for hydrogen evolution under visible light

Photocatalytic H_(2) evolution from seawater splitting presents a promising approach to tackle the fossil energy crisis and mitigate carbon emission due to the abundant source of seawater and sunlight on the earth.However,the development of efficient photocatalysts for seawater splitting remains a formidable challenge.Herein,a 2D/2D ZnIn_(2)S_(4)/WO_(3)(ZIS/WO_(3))heterojunction nanostructure is fabricated to efficiently separate the photoinduced carriers by steering electron transfer from the conduction band minimum of WO_(3) to the valence band maximum of ZIS via constructing internal electric field.Subsequently,plasmonic Au nanoparticles(NPs)as a novel photosensitizer and a reduction cocatalyst are anchored on ZIS/WO_(3) surface to further enhance the optical absorption of ZIS/WO_(3) heterojunction and accelerate the catalytic conversion.The obtained Au/ZIS/WO_(3) photocatalyst exhibits an outstanding H_(2) evolution rate of 2610.6 or 3566.3μmol g^(-1)h~(-1)from seawater splitting under visible or full-spectrum light irradiation,respectively.These rates represent an impressive increase of approximately 7.3-and 6,6-fold compared to those of ZIS under the illumination of the same light source.The unique 2D/2D structure,internal electric field,and plasmonic metal modification together boost the photocatalytic H_(2) evolution rate of Au/ZIS/WO_(3),making it even comparable to H_(2) evolution from pure water splitting.The present work sheds light on the development of efficient photocatalysts for seawater splitting.

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.

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.

Decorating non-noble metal plasmonic Al on a TiO2/Cu2O photoanode to boost performance in photoelectrochemical water splitting

Designing low-cost and high-performance photoelectrodes with improved light harvesting and charge separation rates is significant in photoelectrochemical water splitting.Here,a novel TiO2/Cu2O/Al/Al2O3 photoelectrode is manufactured by depositing plasmonic nanoparticles of the non-noble metal Al on the surface of a TiO2/Cu2O core/shell heterojunction for the first time.The Al nanoparticles,which exhibit a surface plasmon resonance(SPR)effect and are substantially less expensive than noble metals such as Au and Ag,generate hot electron-hole pairs and amplify the electromagnetic field at the interface under illumination.The as-prepared TiO2/Cu2O/Al/Al2O3 photoelectrodes have an extended absorption range and enhanced carrier separation and transfer.Their photocurrent density of 4.52 mA·cm^-2 at 1.23 V vs.RHE represents an 1.84-fold improvement over that of TiO2/Cu2O.Specifically,the ultrathin Al2O3 passivation layer spontaneously generated on the surface of Al in air could act as a protective layer to significantly increase its stability.In this work,the synergistic effect of the heterojunctions and the SPR effect of the non-noble metal Al significantly improve the photoelectrode performance,providing a novel concept for the design of electrodes with good properties and high practicability.

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.

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.