Waveguide-coupled Surface Plasmon Resonance Research Articles

All Optic-Fiber Waveguide-Coupled SPR Sensor for CRP Sensing Based on Dielectric Layer and Poly-Dopamine

We developed an all optic-fiber waveguide-coupled surface plasmon resonance (SPR) sensor using zirconium disulfide (ZrS2) and poly-dopamine (PDA) as the dielectric layer and biological cross-linker, respectively. This sensor can be employed to monitor the entire process of the C-reactive protein (CRP) sensing, including antibody modification and antigen detection. The design and the optimization of the optical fiber waveguide-coupled SPR sensor were realized, based on the transfer matrix method and first-principles calculations. The sensor was fabricated and characterized according to the optimized parameters. The experimental setup was implemented to measure the entire process of antibody modification and antigen detection for CRP with the detection limit of 3.21 pmol·mL−1, and the specificity tests were also carried out.

Surface Plasmon Field-Enhanced Raman Scattering Co-Excited by P-Polarized and S-Polarized Light Based on Waveguide-Coupled Surface Plasmon Resonance Configuration.

We constructed a waveguide-coupled surface plasmon resonance (WCSPR) structure to enhance Raman scattering. In this structure, P-polarized and S-polarized incident lasers can simultaneously coexcite the evanescent field, thereby further enhancing Raman scattering. This configuration is a five-phase Kretschmann resonance setup that consists of a SF10 prism/inner Ag film/SiO2 film/outer Ag film/water structure. The WCSPR configuration effectively concentrates and confines the evanescent field excited by the incident light. Ag nanoparticles assembled on the outer Ag film surface enhance the evanescent field further by means of surface plasmon resonance. By finely tuning the thickness of the Ag and SiO2 films, it is possible to achieve a coincidence between the SPR angle of P-polarized light and that of S-polarized light. At this angle, both P- and S-polarized light can jointly elevate the evanescent field intensity, leading to the simultaneous enhancement of the electric fields at the upper, lower, left, and right parts of the silver nanoparticles and generating maximum evanescent field enhancement. We achieved an electric field enhancement of up to 103 around the nanoparticles, leading to more SERS hotspots and comparable SERS enhancement capability to gap-type hotspots. Our WCSPR structure combined with the nanoparticles offers a feasible strategy for the SERS detection of large molecules that cannot be placed in traditional gap-type hotspots. It is highly convenient for SERS detection of large molecules.

Symmetrical dual D-shape fiber for waveguide coupled surface plasmon resonance sensing

A waveguide-coupled surface plasmon resonance (WCSPR) sensor consisting of two D-shape single-mode fibers is designed and analyzed by the finite element method (FEM). The optical field of the surface plasmon polaritons (SPPs) mode is confined in the dielectric cavity between the dual metallic thin films. Therefore, the effective refractive index of the SPP mode depends largely on the refractive index of the analyte and an anomalous dispersion relationship is observed between the SPP mode and x-polarized core-guide mode of the dual D-shape fiber. The excitation mechanism of surface plasmon resonance (SPR) in the coupling region is attributed to phase matching of the two modes. Further analysis shows that the narrow bandwidth peak in the loss spectrum of the core mode is determined by the sensor dimensions contributed jointly by the thicknesses of the silver film, dielectric layer, and titanium dioxide film. Compared to the single-fiber structure, the optimized dual D-shape WCSPR sensor achieves a maximum wavelength sensitivity of 52,200 nm/RIU with a full-width at half-minimum (FWHM) of 9.47 nm and a figure of merit (FOM) of 346.6 RIU−1 in the analyte refractive index range of 1.32–1.42.

Double Fano sensing mechanism of waveguide coupled surface plasma

Based on the optical properties of waveguide-coupled surface plasmon resonance, a sensor of surface plasmon coupled waveguide resonance with double discrete states generated by the upper and lower waveguide structures combined with prisms and Au films, respectively, is proposed. In this paper, the sensing structure is studied numerically and analytically, and the transmission characteristics of surface equipartition excitations are analyzed and elaborated in-depth in combination with the reflection angle spectrum, as well as the generation and evolution mechanism of dual Fano resonance at different incidence angles at fixed wavelengths. The structural model of Fano resonance sensing based on angle modulation is established, and the sensing characteristics are analyzed to produce electromagnetic field enhancement at low-angle Fano. The mathematical model between structural parameters and spectral performance is established using back propagation (BP) neural network, and the particle swarm optimization (PSO) algorithm is used to find the input structural parameters corresponding to the optimal performance, The results show that the quality factor of resonance (FOM) and sensitivity is significantly improved; When it is used in the field of biosensing, the response curves of Fano with different angles of high and low to concentration are quite different, thus realizing high precision detection of different concentrations of solutions and reflecting excellent sensing performance.

Propagating and Localized Surface Plasmon Co-Enhanced Raman Scattering Based on a Waveguide Coupling Surface Plasmon Resonance Structure

We propose a waveguide-coupled surface plasmon resonance (WCSPR) structure with MgF2 as the waveguide layer to enhance Raman scattering. The WCSPR was a five-layer resonance structure composed of prism/Ag film/MgF2 film/outer Ag film layers. The electromagnetic field was stronger with the WCSPR structure than with a traditional SPR structure. Furthermore, localized and propagating surface plasmon co-enhanced Raman scattering of 4-mercaptopyridine was observed on the WCSPR/4-Mpy/silver-nanoparticle sandwich structure. The most effective coupling of the localized and propagating surface plasmons resulted in a 60-fold enhancement in the signal intensity relative to that obtained with a conventional SPR structure. The enhancement factor of the WCSPR/4-Mpy/silver-nanoparticle configuration was 3.6 × 107.

Plasmonic mode coupling and thin film sensing in metal\u2013insulator\u2013metal structures

Optical sensors based on surface plasmon resonance (SPR) in the attenuated total reflection (ATR) configuration in layered media have attracted considerable attention over the past decades owing to their ability of label free sensing in biomolecular interaction analysis, and highly sensitive detection of changes in refractive index and thickness, i.e. the optical thickness, of thin film adsorbates (thin film sensing). Furthermore, SPR is highly sensitive to the refractive index of the medium adjacent to the bare metal, and it allows for bulk sensing as well. When deposited at the metal/air interface, an adsorbed layer disturbs the highly localized, i.e. bound, wave at this interface and changes the plasmon resonance to allow for sensing in angular or wavelength interrogation and intensity measurement modes. A high degree of sensitivity is required for precise and efficient sensing, especially for biomolecular interaction analysis for early stage diagnostics; and besides conventional SPR (CSPR), several other configurations have been developed in recent years targeting sensitivity, including long-range SPR (LRSPR) and waveguide-coupled SPR (WGSPR) observed in MIM structures, referred here to by MIM modes, resulting from the coupling of SPRs at I/M interfaces, and Fano-type resonances occurring from broad and sharp modes coupling in layered structures. In our previous research, we demonstrated that MIM is better than CSPR for bulk sensing, and in this paper, we show that CSPR is better than MIM for thin film sensing for thicknesses of the sensing layer (SL) larger than 10 nm. We discuss and compare the sensitivity of CSPR and MIM for thin film sensing by using both experiments and theoretical calculations based on rigorous electromagnetic (EM) theory. We discuss in detail MIM modes coupling and anti-crossing, and we show that when a thin film adsorbate, i.e. a SL), is deposited on top of the outermost-layer of an optimized MIM structure, it modifies the characteristics of the coupled modes of the structure, and it reduces the electric field, both inside the SL and at the SL/air interface, and as a result, it decreases the sensitivity of the MIM versus the CSPR sensor. Our work is of critical importance to plasmonic mode coupling using MIM configurations, as well as to optical bio- and chemical-sensing.

High figure of merit observed in SBN thin film based EO modulator employing WCSPR technique

Present work demonstrates an efficient Waveguide coupled Surface Plasmon Resonance (WCSPR) based electro-optic (EO) modulator device utilizing Strontium Barium Niobate (SBN) films with enhanced figure of merit. Pulsed laser deposition (PLD) technique was employed to monitor the effect of incident laser fluence from 1.4Jcm-2 to 1.6Jcm-2 on the crystallographic property of Sr0.75Ba0.25Nb2O6(SBN75). For comparison Sr0.60Ba0.40Nb2O6(SBN60) thin film deposited under optimized conditions were also utilized for studying the characteristics of developed WCSPR-EO modulator. Enhancement in the resolution of the WCSPR-EO system from 1.61RIU-1 for SBN60 thin film to 0.59RIU-1 for SBN75 thin film has been obtained. Improved Figure of merit (FOM) with higher sensitivity of about 47.5° and maximum modulation index of 41.73% estimated for prism/air–gap/Au/SBN75/LSCO/Si (WCSPR-EO) modulator system which paves a way for potential application of SBN75 thin film for optoelectronic devices.

Influence of Design Parameters on Multilayered Nanoplasmonic Structures in Modified Kretschmann-Raether Configurations

Surface Plasmon Resonance (SPR) technique has been of recent interest in many fields such as biological and chemical sensing, defense-related applications, etc. The introduction of graphene sheet (metal-like optical properties) over a thin-film layers plays a significant role in generating SPR. Different nanoplasmonic structures like Coupled Waveguide SPR (CWSPR) and Long Range SPR (LRSPR) are considered with modified Kretschmann-Raether configurations for different wavelengths in visible range for plasmonic sensors application. Characteristic Transfer Matrix (CTM) method in MATLAB environment is employed to obtain the theoretical results of LRSPR-based nanoplasmonic structures. Based on different compositions, minimum reflectivity as obtained is reported here. Due to the incorporation of additional graphene thin layer, keeping the angle of incidence constant, the percentage of reflectivity is being increased significantly, thereby reducing the transmission within the layers. With the variation of thickness, refractive index of different layers as well as wavelength of the LASER source, one may optimize the structures to obtain best possible performance.

Waveguide-Coupled Surface Plasmon Resonance Sensor for Both Liquid and Gas Detections

In this paper, we propose a novel surface plasmon resonance sensor for both liquid and gas detections, which is based on the two dielectric planar waveguide (PWG)-coupled plasmonic structure. Two sharp Fano-type resonances, which arise from the electromagnetic coupling between surface plasmon polariton (SPP) and PWG modes, appear in the reflection curve, and they can be used to monitor the minute changes of the refractive indices of gas and liquid due to their high imaging sensitivities (> 9.0 × 103 RIU− 1). The Fano resonance angles and the figures of merit for imaging sensitivity can be effectively manipulated by the thicknesses of guiding layers, and the sensor system can measure over a wide range of the refractive indices of sensing media.

Surface Plasmon Field-Enhanced Raman Scattering Based on Evanescent Field Excitation of Waveguide-Coupled Surface Plasmon Resonance Configuration

We propose a bimetallic waveguide-coupled surface plasmon resonance (WCSPR) configuration to enhance Raman scattering with an evanescent field excited using surface plasmons. The WCSPR configuratio...

Thermo-optic Aided Tunability of Sr0.6Ba0.4Nb2O6 Thin Film-based Electro-optic Modulator Using Waveguide Coupled SPR Modes

Present article demonstrates the effective tuning of thermo-optic (TO) properties with the Electro-Optic (EO) modulation characteristics of SBN60 thin films utilizing Waveguide coupled surface plasmon resonance (WCSPR) technique. Electro-optic (EO) coefficient (r) was in turn tuned from a value of 594 pm/V to 621 pm/V with increasing ambient temperature from 296 to 373 K. Tunable percent modulation index varying from 24 to 55% was obtained with increasing ambient temperature at a fixed applied electric field. The obtained results clearly illustrate an efficient thermally tunable EO modulator based on SBN thin film utilizing a simplistic approach with $$ {\left.\kern0em \left(\frac{\partial n}{\partial T}\right)\right|}_{E=0}=88.3\times {10}^{-4}{K}^{-1} $$.

Ferroelectric [formula omitted] thin film based broadband waveguide coupled surface plasmon electro-optic modulator

Present article demonstrates the enhanced dynamically tuneable EO modulation characteristics in ferroelectric Strontium Barium Niobate SBN,Sr0.6Ba0.4Nb2O6 thin film modulator based on waveguide coupled surface plasmon resonance. The alternating modulating signals having broad frequency range (1 kHz to 10 MHz) with varying amplitude (40kV/cm to 400kV/cm) was applied to estimate the resonance frequency (~1 MHz) using differential modulated intensity interrogation signal. A high value of EO coefficient r=310pm/V leading to Modulation index of 56% was achieved with sensitivity of about 0.33 at resonance possessing a characteristics length of 54.64 μm. These waveguide modes coupled with the plasmon modes paves a way for development of EO modulators utilizing materials with high losses. Therefore, a thin film based WCSPR-EO modulator with compact footprint, low operation voltage, broad operation spectrum and faster speed of modulation was fabricated which paves the way for on-chip optical communications.

Tunable Fano resonances and improved sensitivity in waveguide-coupled surface plasmon resonance sensors with a bimetallic layer

A multilayer structure consisting of Au–Ag bimetal and dielectric layers which allows coupling between surface plasmon polaritons and waveguide modes is studied by calculating reflectivity curves of incident light. The coupling results in asymmetric resonance modes, which can be attributed to Fano resonances (FR). The variation trend of FR is investigated in detail by fitting numerical results with an analytic model when changing both waveguide widths and silver thicknesses. It is demonstrated that changing the thickness ratio of Au–Ag bilayers can tune the coupling strength and the line shape of FR. We build the resonant mode diagram according to the different asymmetric line shape which can be depicted by the sign of the fitting Fano constant q. At a critical Ag thickness, the coupling gives rise to a q = 0 symmetrical resonance state (plasma induced transparency). Finally, the best optimized thickness combination (Ag/Au) in the structure is found when the refractive index of the sensing layer medium changes. The sensitivity of the optimized sensor is twice as high as that of the single Au film structure.

Highly sensitive biosensor with graphene-MoS2 heterostructure based on photonic spin Hall effect

Abstract We propose a new optical biosensor based on photonic spin Hall effect (PSHE) for detection of DNA hybridization. This device consists of BK7 prism, Ag, SiO2, Au and graphene-MoS2 heterostructure which produces waveguide coupled surface plasmon resonance (WCSPR) effect to enormously enhance PSHE. The adsorption of graphene-MoS2 heterostructure to biomolecules changes the refractive index of the sensing medium, thereby affecting spin-dependent splitting in PSHE. The 2 × 2 transfer matrix method is applied to calculate the generalized Fresnel reflection and we deduce the reflected light shifts in PSHE. We study the correlation between spin-dependent displacements and the refractive index variations of sensed solution to obtain the highest sensitivity in the proposed sensor. However, the PSHE exists in the proposed biosensor is extremely weak, so a signal enhancement technology called weak measurement is adopted to amplify the PSHE shift. Thus, the proposed biosensor can successfully detect the hybridization of probe DNA with target DNA. These results may provide practical applications for PSHE in biological monitoring, medical diagnosis, and food safety.

Theoretical and Experimental Investigation of an All-Fiber Waveguide Coupled Surface Plasmon Resonance Sensor With Au–ZnO–Au Sandwich Structure

In this paper, we proposed an all-fiber waveguide coupled surface Plasmon resonance (SPR) sensor which was designed and fabricated with Au-ZnO-Au sandwich multi-layer structure. Based on the transfer matrix method (TMM), the theoretical modeling of the proposed sensor structure was investigated. The influence of the layer thickness on the transmission spectrum of the sensor was studied numerically, in order to optimize each layer thickness, leading to sensitivity enhancement in the infrared spectral range. Meanwhile, an experimental testbed for the refractive index measurement was implemented based on the proposed all-fiber waveguide coupled SPR sensor. Using this waveguide coupled SPR sensor, the refractive index sensing was realized with a sensitivity enhancement of 7%—131% compared with conventional SPR sensors.

Fano Resonance Enhanced Surface Plasmon Resonance Sensors Operating in Near-Infrared

In the phase-sensitivity-based surface plasmon resonance (SPR) sensing scheme, the highest phase jump usually happens at the darkness or quasi-darkness reflection point, which results in low power for detection. To overcome such a limitation, in this paper, a waveguide-coupled SPR configuration is proposed to work at near-infrared. The coupling between surface plasmon polariton (SPP) mode and photonic waveguide (PWG) mode results in electromagnetically induced transparency (EIT) and asymmetric Fano resonance (FR). Near the resonance, the differential phase between p-polarized and s-polarized incident waves experience drastic variation upon change of the surrounding refractive index. More importantly, since the FR occurs at the resonance slope of SPP mode, the corresponding phase change is accompanied with relatively high reflectivity, which is essential for signal-to-noise ratio (SNR) enhancement and power consumption reduction. Phase sensitivity up to 106 deg/RIU order with a minimum SPR reflectivity higher than 20% is achieved. The proposed scheme provides an alternative approach for high-performance sensing applications using FR.

Waveguide coupled surface plasmon resonance based electro optic modulation in SBN thin films

Modulation of light intensity utilizing Waveguide Coupled Surface Plasmon Resonance (WCSPR) technique at low driving voltage has been demonstrated in the present work. The high value of electro optic coefficient of Strontium Barium Niobate Sr0.6Ba0.4Nb2O6(SBN60) makes it a promising material for the SPR based electro optic modulators. Prism coupling technique has been utilized for the excitation of surface plasmons in Strontium Barium Niobate (SBN) thin film in Otto configuration. Modulation of about 36% is observed due to a significant change in the refractive index of SBN60 thin film on application of electric field of 200 kV/cm. The transient response of change in reflectivity of the WCSPR system with electric field indicates the dynamic change of polarization state of SBN thin film.

A Waveguide-Coupled Surface Plasmon Resonance Sensor Using an Au-MgF2-Au Structure

We describe an Au-MgF2-Au trilayered waveguide-coupled surface plasmon resonance (WCSPR) sensor in this article. The characteristics of this sensing structure are compared with those of the conventional single-layered gold surface plasmon resonance (SPR) sensor theoretically and experimentally. The experiment results show that WCSPR can provide not only seven times smaller refractive index resolution in the bulk sensing application but also more accurate measurement results for the biomolecular interaction analysis than the conventional single-layered gold SPR. What’s more, this high-resolution sensor is easy to build and not sensitive to film thickness variations. The Au-MgF2-Au trilayered WCSPR may provide a simple and convenient chip-based strategy for performance enhancement of SPR sensors without varying the hardware and software of measurement instruments.

Enhanced resolution of a surface plasmon resonance sensor detecting C-reactive protein via a bimetallic waveguide-coupled mode approach

Extensive efforts have been devoted to improving the resolution of surface plasmon resonance (SPR) sensors in the detection of trace levels of biomolecules considered essential for the early diagnosis of disease. As part of these efforts, we previously developed a bimetallic waveguide-coupled surface plasmon resonance (Bi-WCSPR) sensor configuration designed to dramatically reduce the linewidth of the SPR curve while preserving a moderate local field decay length, thereby addressing the resolution issue. In this study, we systematically quantified the enhanced resolution in Bi-WCSPR sensors used to detect C-reactive protein (CRP), a widely accepted biomarker of inflammation in cardiovascular disease. Individual SPR sensorgrams were measured at several CRP concentrations in both the intensity and angular interrogation modes, confirming that the Bi-WCSPR configuration with a high Ag-to-Au ratio provided a figure-of-merit (FOM) that was 2.53 times higher than that of conventional Au sensors and a limit-of-detection (LOD) that was an order of magnitude lower than the cut-off level for CRP. It was found that when using the Bi-WCSPR configurations, the resolution enhancement in the intensity interrogation mode becomes more evident as the CRP concentrations is lowered to the cut-off level.

Characteristics of multiple Fano resonances in waveguide-coupled surface plasmon resonance sensors based on waveguide theory

We observe and analyze multiple Fano resonances and the plasmon-induced transparency (PIT) arising from waveguidecoupled surface plasmon resonance in a metal-dielectric Kretschmann configuration. It is shown that the simulation results for designed structures agree well with those of the dispersion relation of waveguide theory. We demonstrate that the coupling between the surface plasmon polariton mode and multi-order planar waveguide modes leads to multiple Fano resonances and PIT. The obtained results show that the number of Fano resonances and the linewidth of resonances depend on two structural parameters, the Parylene C and SiO2 layers, respectively. For the sensing action of Fano resonance, the figure of merit for the sensitivity by intensity is estimated to be 44 times higher than that of conventional surface plasmon resonance sensors. Our research reveals the potential advantage of sensors with high sensitivity based on coupling between the SPP mode and multi-order PWG modes.