Highly sensitive and stable probe refractometer based on configurable plasmonic resonance with nano-modified fiber core

A dispersion model is developed to provide a generic tool for configuring plasmonic resonance spectral characteristics.The customized design of the resonance curve aiming at specific detection requirements can be achieved.According to the model,a probe-type nano-modified fiber optic configurable plasmonic resonance(NMF-CPR)sensor with tip hot spot enhancement is demonstrated for the measurement of the refractive index in the range of 1.3332-1.3432 corresponding to the low-concentration biomarker solution.The new-type sensing structure avoids excessive broadening and redshift of the resonance dip,which provides more possibilities for the surface modification of other functional nanomaterials.The tip hot spots in nanogaps between the Au layer and Au nanostars(AuNSs),the tip electric field enhancement of AuNSs,and the high carrier mobility of the WSe_(2)layer synergistically and significantly enhance the sensitivity of the sensor.Ex-perimental results show that the sensitivity and the figure of merit of the tip hot spot enhanced fiber NMF-CPR sensor can achieve up to 2995.70 nm/RIU and 25.04 RIU^(−1),respectively,which are 1.68 times and 1.29 times higher than those of the conventional fiber plasmonic resonance sensor.The results achieve good agreements with numerical simulations,demonstrate a better level compared to similar reported studies,and verify the correctness of the dispersion model.The detection resolution of the sensor reaches up to 2.00×10^(−5)RIU,which is obviously higher than that of the conventional side-polished fiber plasmonic resonance sensor.This indicates a high detection accuracy of the sensor.The dense Au layer effectively prevents the intermediate nanomaterials from shedding and chemical degradation,which enables the sensor with high stability.Furthermore,the terminal reflective sensing structure can be used as a practical probe and can allow a more convenient operation.

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.

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.

Au nanoring arrays with tunable morphological features and plasmonic resonances

Gold nanoring arrays are widely applied in various fields benefitting from their localized surface plasmon resonance(LSPR)properties.A key advantage of gold nanoring arrays is that the dipole resonance peak can be systematically tuned by changing the dimensions of gold nanoring arrays.However,most of the currently reported methods for preparing gold nanoring arrays cannot conveniently control the heights of the nanorings at a low cost.Here we introduce a facile method for preparing gold nanoring arrays with tunable plasmonic resonances using colloidal lithography.The dimensions of the nanorings including diameters,lattice constants,even the heights of the nanorings can be conveniently varied.Fourier transform near-infrared(FT-NIR)absorption spectroscopy was used to obtain the plasmonic resonance spectra of the nanoring arrays.All the prepared gold nanoring arrays exhibited a strong NIR or infrared(IR)plasmonic resonance which can be tuned by varying the nanoring dimensions.This versatile method can also be used to fabricate other types of plasmonic nanostructures,such as gold nanocone arrays.The obtained gold nanoring arrays as well as nanocone arrays may have potential applications in surface-enhanced spectroscopy or plasmonic sensing.

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.

Fiber cladding dual channel surface plasmon resonance sensor based on S-type fiber

Fiber cladding surface plasmon resonance(SPR)sensors have few structures,and a clad SPR sensor based on S-type fiber is proposed in this paper.This new type of fiber cladding SPR sensor was formed by electrofusing an S-shaped structure on the fiber to couple the light in the fiber core to the cladding.In this paper,the effects of fiber parameters on the performance of the sensor were studied by simulation and experiment.Based on the conclusion that the smaller the core diameter is,the closer the working band of the SPR resonance is to long wavelengths,and that the geometric characteristics mean that a multimode fiber can receive the fiber cladding light from a small core diameter few-mode fiber,a dual channel SPR sensor with a double S-type fiber cascade was proposed.In the refractive index detection range of 1.333–1.385refractive index units(RIU),the resonant working band of channel I is 627.66 nm–759.78 nm,with an average sensitivity of 2540.77 nm/RIU,and the resonant working band of channel II is 518.24 nm–658.2 nm,with an average sensitivity of2691.54 nm/RIU.The processing method for the S-type fiber cladding SPR sensor is simple,effectively solving the problem of this type of SPR sensor structure and the difficult realization of a dual channel.The sensor is expected to be used in the fields of medical treatment and biological analysis.

Dual-channel fiber-optic surface plasmon resonance sensor with cascaded coaxial dual-waveguide D-type structure and microsphere structure

To address the restriction of fiber-optic surface plasmon resonance(SPR) sensors in the field of multi-sample detection, a novel dual-channel fiber-optic SPR sensor based on the cascade of coaxial dual-waveguide D-type structure and microsphere structure is proposed in this paper. The fiber sidepolishing technique converts the coaxial dual-waveguide fiber into a D-type one, and the evanescent wave in the ring core leaks, generating a D-type sensing region;the fiber optic fused ball push technology converts the coaxial dual waveguides into microspheres, and the stimulated cladding mode evanescent wave leaks, producing the microsphere sensing region. By injecting light into the coaxial dual-waveguide middle core alone, the sensor can realize single-stage sensing in the microsphere sensing area;it can also realize dual-channel sensing in the D-type sensing area and microsphere sensing area by injecting light into the ring core. The refractive index measurement ranges for the two channels are 1.333–1.365 and 1.375–1.405, respectively, with detection sensitivities of 981.56 nm/RIU and 4138 nm/RIU. The sensor combines wavelength division multiplexing and space division multiplexing technologies, presenting a novel research concept for multi-channel fiber SPR sensors.

Resonance properties of THz plasmonic dipole-bowtie antenna array: The critical role of the substrate

Subwavelength arrays of dipole-bowtie antennas are designed and characterized using terahertz time-domain spectroscopy（THz-TDS） and finite element method（FEM） simulations. Two different substrates, silicon and mylar with an order of magnitude difference between their thickness values are used to study the resonance properties of the antennas.The 640-μm thick silicon substrate supports a sharper fundamental mode resonance. We discover that higher-order Fabry–Perot resonances can be excited only in 24-μm thin mylar substrates and show much higher sensitivity to dielectric changes in the environment and the geometrical parameters of the antennas than the fundamental dipole resonance.

Numerical simulation of a truncated cladding negative curvature fiber sensor based on the surface plasmon resonance effect

A refractive index(RI)sensor based on the surface plasmon resonance effect is proposed using a truncated cladding negative curvature fiber(TC-NCF).The influences of the TC-NCF structure parameters on the sensing performances are investigated and compared with the traditional NCF.The simulation results show that the proposed TC-NCF RI sensor has an ultra-wide detection range from 1.16 to 1.43.The maximum wavelength sensitivity reaches 12400 nm/RIU,and the corresponding R^(2)of the polynomial fitting equation is 0.9999.The maximum and minimum resolutions are 2.56×10^(-5)and 8.06×10^(-6),respectively.In addition,the maximum amplitude sensitivity can reach-379.1 RIU^(-1)when the RI is chosen as 1.43.The proposed TC-NCF RI sensor could be useful in biochemical medicine,environmental monitoring,and food safety.

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.

Facile fabrication of large-area hierarchical plasmonic cavities with broadband plasmon resonance for enhanced photocatalytic hydrogen evolution

Integrating hierarchical plasmonic cavities into photocatalysis offers a promising avenue for expanding the light utilization range to cover the entire solar spectrum. However, fabricating these nanostructures with seamless size transitions for a wide plasmon resonant range remains technically challenging, requiring precise nanofabrication control and often relying on expensive and laborious techniques like e-beam lithography and reactive ion etching. Herein, a one-step forming strategy was explored to fabricate simple yet hierarchical plasmonic cavities featuring the surface nanodome array-integrated plasmonic Fabry–Pérot cavity through a facile large-area nanoimprinting method. This design leverages a uniform feature size and periodic arrangement to broaden the light utilization range of TiO_(2) across the entire solar spectrum (200–2500 nm). It consists of an upper nanodome array cavity with vertically continuous graded sizes for broadband absorption (200–1500 nm), coupled with a bottom plate cavity that enlarges the overall cavity size to extend the range to 2500 nm. Remarkably, simply adjusting the thickness of the plate cavity can tune the resonant position, eliminating the need for expensive mold modifications. When combined with TiO_(2), this hierarchical plasmonic cavity significantly enhances the photocatalytic hydrogen evolution rate to 36.3 µmol/h, achieving a remarkable 9.8-fold increase compared to pure TiO_(2) under full-spectrum illumination. This approach offers a convenient and inexpensive alternative to sophisticated nanofabrication techniques for large-area hierarchical plasmonic cavities with broadband plasmon resonance to enhance the photocatalytic hydrogen evolution.

Characterization of squash polysaccharide and the anti-diabetic effect on type 2 diabetic rat revealed by urine metabolomics analysis

The present study reports the structural characteristics of 3 polysaccharide fractions(SPS-F1,SPS-F2 and SPS-F3)isolated and purified from squash.SPS-F1(molecular weight(Mw)=12.30 kDa)and SPS-F2(Mw=19.40 kDa)were likely to contain HG and RG-I domain of pectic polysaccharide,respectively.SPS-F2(Mw=270.4 kDa)was mainly composed of rhamnose,galactose and arabinose.The treatment with SPS decreased body weight gain,glucose and TG levels in type 2 diabetes rats.Besides,25 differential metabolites were identified based on urinary metabolomics analysis,which are crucial to the anti-diabetic effect of SPS.The regulation of nicotinamide N-oxide,histamine,cis-aconitate,citrate,L-malic acid,3-(3-hydroxyphenyl)propanoic acid and N-acetyl-L-aspartic acid were mainly associated with energy metabolism,gut microbiota and inflammation.Study of surface plasmon resonance revealed the binding kinetics with galectin-3(Gal-3)and fibroblast growth factor 2(FGF2).The K_(D)values of SPS-F2 and SPS-F3 to Gal-3 were 4.97×10^(-3)and 1.48×10^(-3)mol/L,indicating a weak binding affinity.All 3 fractions showed moderate binding to FGF2 and the affinity was SPS-F3>SPS-F2>SPS-F1.Thus,the metabolomics and SPR approach were proved to be a promising tool in exploring the anti-diabetes effects of SPS and provided a deep understanding of the mechanisms.

A Multifunctional Chiral Metasurface with Asymmetric Transmission and Linear-Polarization Conversion

In this paper,a multifunctional chiral metasurface is presented to achieve asymmetric transmission(AT)and linear-polarization conversion(LPC).The designed metasurface consists of a cross swords-like shape and two holes in the lower side of the unit cell.In the frequency band from 8.3 GHz to 10.4 GHz,AT is realized with more than 90%efficiency and the same chiral metasurface transforms linear polarized wave into its orthogonal counterpart with high efficiency.For LPC,the polarization conversion ratio(PCR)is greater than 95%.The proposed metasurface is stable against the incident angles of striking electromagnetic(EM)waves up to 60°for both operations of AT and LPC.

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.

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.

On-chip readout plasmonic mid-IR gas sensor

Gas identification and concentration measurements are important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change.Here a novel mid-IR plasmonic gas sensor with on-chip direct readout is proposed based on unity integration of narrowband spectral response,localized field enhancement and thermal detection.A systematic investigation consisting of both optical and thermal simulations for gas sensing is presented for the first time in three sensing modes including refractive index sensing,absorption sensing and spectroscopy,respectively.It is found that a detection limit less than 100 ppm for CO2 could be realized by a combination of surface plasmon resonance enhancement and metal-organic framework gas enrichment with an enhancement factor over 8000 in an ultracompact optical interaction length of only several microns.Moreover,on-chip spectroscopy is demonstrated with the compressive sensing algorithm via a narrowband plasmonic sensor array.An array of 80 such sensors with an average resonance linewidth of 10 nm reconstructs the CO2 molecular absorption spectrum with the estimated resolution of approximately 0.01 nm far beyond the state-of-the-art spectrometer.The novel device design and analytical method are expected to provide a promising technique for extensive applications of distributed or portable mid-IR gas sensor.

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.

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.

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.