Plasmonic sensor with self-reference capability based on functional layer film composed of Au/Si gratings

We propose a simple one-dimensional grating coupling system that can excite multiple surface plasmon resonances for refractive index(RI)sensing with self-reference characteristics in the near-infrared band.Using theoretical analysis and the finite-difference time-domain method,the plasmonic mechanism of the structure is discussed in detail.The results show that the excited resonances are independent of each other and have different fields of action.The mode involving extensive interaction with the analyte environment achieves a high sensitivity of 1236 nm/RIU,and the figure of merit(FOM)can reach 145 RIU-1.Importantly,the mode that is insensitive to the analyte environment exhibits good self-reference characteristics.Moreover,we discuss the case of exchanging the substrate material with the analyte environment.Promising simulation results show that this RI sensor can be widely deployed in unstable and complicated environments.

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.

A novel plasmonic refractive index sensor based on gold/silicon complementary grating structure

A novel complementary grating structure is proposed for plasmonic refractive index sensing due to its strong resonance at near-infrared wavelength.The reflection spectra and the electric field distributions are obtained via the finite-difference time-domain method.Numerical simulation results show that multiple surface plasmon resonance modes can be excited in this novel structure.Subsequently,one of the resonance modes shows appreciable potential in refractive index sensing due to its wide range of action with the environment of the analyte.After optimizing the grating geometric variables of the structure,the designed structure shows the stable sensing performance with a high refractive index sensitivity of 1642 nm per refractive index unit(nm/RIU)and the figure of merit of 409 RIU^(-1).The promising simulation results indicate that such a sensor has a broad application prospect in biochemistry.

A DNA origami plasmonic sensor with environment-independent read-out

DNA origami is a promising technology for its reproducibility,flexibility,scalability and biocompatibility.Among the several potential applications,DNA origami has been proposed as a tool for drug delivery and as a contrast agent,since a conformational change upon specific target interaction may be used to release a drug or produce a physical signal,respectively.However,its conformation should be robust with respect to the properties of the medium in which either the recognition or the read-out take place,such as pressure,viscosity and any other unspecific interaction other than the desired target recognition.Here we report on the read-out robustness of a tetragonal DNA-origami/gold-nanoparticle hybrid structure able to change its configuration,which is transduced in a change of its plasmonic properties,upon interaction with a specific DNA target.We investigated its response when analyzed in three different media:aqueous solution,solid support and viscous gel.We show that,once a conformational variation is produced,it remains unaffected by the subsequent physical interactions with the environment.

Ultra wide sensing range plasmonic refractive index sensor based on nano-array with rhombus particles

We propose a two-dimensional metal grating with rhombus particles on a gold film structure for refractive index sensing due to its perfect absorption at near-infrared wavelength.Via two-dimensional metal grating coupling,the incident light energy is effectively transformed into the surface plasmons which propagate along the upper surface of the gold film and interact with the surrounding environment in a wide range.The plasmonic resonance mechanism of the structure is discussed in detail by theoretical analysis and finite-difference time-domain method.After optimizing the geometrical parameters,the designed structure shows the sensing performance with a refractive index sensitivity of 1006 nm/RIU.More importantly,this plasmonic refractive index sensor achieves an ultra wide refractive index sensing range from 1.0 to 2.4 with a stable sensing performance.The promising simulation results of the structure show that the sensor has a broad application prospect in the field of biology and chemistry.

A High-Sensitivity Refractive-Index Sensor Based on Plasmonic Waveguides Asymmetrically Coupled with a Nanodisk Resonator

A high-sensitivity plasmonic refractive-index sensor based on the asymmetrical coupling of two metal-insulator- metal waveguides with a nanodisk resonator is proposed and simulated in the finite-difference time domain. Both analytic and simulated results show that the resonance wavelengths of the sensor have an approximate linear relationship with the refractive index of the materials which are filled into the slit waveguides and the disk- shaped resonator. The working mechanism of this sensor is exactly due to the linear relationship, based on which tile refractive index of the materials unknown can be obtained from the detection of the resonance wavelength. The measurement sensitivity can reach as high as 6.45 × 10-7, which is nearly five times higher than the results reported in the recent literature [Opt. Commun. 300 （2013） 265]. With an optimum design, the sensing value can be further improved, and it can be widely applied into the biological sensing. Tile sensor working for temperature sensing is also analyzed.

A Photonic Crystal Fiber Based Asymmetric Slotted Structured Highly Sensitive Refractive Index Plasmonic Biosensor

Surface plasmon resonance (SPR) sensors have grown in popularity owing to their sensitivity, precision, and capacity for a variety of applications, including detection, monitoring, and sensing, among others. Sensitivity and resolution are two areas where this technology has room for development. A plasmonic biosensor based on an asymmetric slotted PCF structure with extremely high sensitivity has been described and theoretically investigated. This high performance sensor is constructed and completely characterized using finite element method in COMSOL Multiphysics software environment. Sensitivity and resolution are analyzed as performance parameters for the proposed sensor. Numerical simulation exhibits the maximum wavelength-sensitivity of 1100 nm/RIU with 9.09 × 10-6 RIU resolution in the broad measurement range of refractive index from 1.30 to 1.44. A polarization controller can be used to fine-tune this extremely sensitive and wide-ranging refractive index sensor to fulfil a variety of practical needs. This is performed with the consideration of the variation in the refractive index (RI) of the analyte channels. In comparison with earlier PCF-based sensors, the fiber design structure is basic, symmetrical, simple to produce, and cost-effective. Because of the asymmetric air holes and higher sensitivities of the refractive index detector, it is possible to identify biomolecules, biochemicals and other analytes.

Photonic spin Hall effect and terahertz gas sensor via InSb-supported long-range surface plasmon resonance

We propose a simple one-dimensional grating coupling system that can excite multiple surface plasmon resonances for refractive index(RI)sensing with self-reference characteristics in the near-infrared band.Using theoretical analysis and the finite-difference time-domain method,the plasmonic mechanism of the structure is discussed in detail.The results show that the excited resonances are independent of each other and have different fields of action.The mode involving extensive interaction with the analyte environment achieves a high sensitivity of 1236 nm/RIU,and the figure of merit(FOM)can reach 145 RIU-1.Importantly,the mode that is insensitive to the analyte environment exhibits good self-reference characteristics.Moreover,we discuss the case of exchanging the substrate material with the analyte environment.Promising simulation results show that this RI sensor can be widely deployed in unstable and complicated environments.

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.

Sensitivity improvement of aluminum-based far-ultraviolet nearly guided-wave surface plasmon resonance sensor

An aluminum(Al)based nearly guided-wave surface plasmon resonance(NGWSPR)sensor is investigated in the far-ultraviolet(FUV)region.By simultaneously optimizing the thickness of Al and dielectric films,the sensitivity of the optimized Al-based FUV-NGWSPR sensor increases from 183/RIU to 309/RIU,and its figure of merit rises from 26.47 RIU^(-1)to 32.59 RIU^(-1)when the refractive index of dielectric increases from 2 to 5.Compared with a traditional FUV-SPR sensor without dielectric,the optimized FUV-NGWSPR sensor can realize simultaneous improvement of sensitivity and figure of merit.In addition,the FUV-NGWSPR sensor with realistic materials(diamond,Ta_(2)O_(5),and GaN)is also investigated,and 137.84%,52.70%,and 41.89%sensitivity improvements are achieved respectively.This work proposes a method for performance improvement of FUV-SPR sensors by exciting nearly guided-wave,and could be helpful for the high-performance SPR sensor in the short-wavelength region.

Performance analysis of surface plasmon resonance sensor with high-order absentee layer

A surface plasmon resonance （SPR） sensor with a high-order absentee layer on the top of metallic film is proposed. The performance of the SPR sensor with NaCl, MgO, TiO2 or AlAs high-order absentee layer is analyzed theoretically. The results indicate that the sensitivity and the full width at half maximum of those SPR sensors decrease with the increasing of the order of absentee layer, but the variation of the figure of merit （FOM） depends on the refractive index of absentee layer. By improving the order of absentee layer with high-refractive-index, the FOM of the SPR sensor can be enhanced. The maximum value of FOM for the SPR sensor with high-order TiO2 （or AlAs） absentee layer is 1.059% （or 2.587%） higher than the one with one-order absentee layer. It is believed the proposed SPR sensor with high-order absentee layer will be helpful for developing the high-performance SPR sensors.

Highly Sensitive Refractive Index Sensor Based on Plasmonic Bow Tie Configuration

We propose a highly refractive index sensor based on plasmonic Bow Tie configuration.The sensitivity of the resonator design is enhanced by incorporating a nanowall(NW)in a modified Bow Tie design where sharp tips of V-junction are flattened.This approach provides high confinement of electric field distribution of surface plasmon polariton(SPP)mode in the narrow region of the cavity.Consequently,the effective refractive index(neff)of the mode increases and is highly responsive to the ambient medium.The sensitivity analysis of the SPP mode is calculated for six resonator schemes.The results suggest that the NW embedded cavity offers the highest mode sensitivity due to the large shift of effective index when exposed to a slight change in the medium refractive index.Moreover,the device sensitivity of the proposed design is approximated at 2300 nm/RIU which is much higher than the sensitivity of the standard Bow Tie configuration.

Synthesis of high-purity silver nanorods with tunable plasmonic properties and sensor behavior

Through anisotropic Ag overgrowth on the surface of Au nanobipyramids(Au NBPs), high-purity and sizecontrolled Ag nanorods(Au/Ag NRs) are obtained by a simplified purification process. The diameters of the Au/Ag NRs are determined by the size of the as-prepared Au NBPs, and the lengths of the Au/Ag NRs are tunable using different amounts of Ag precursor in the growth solution. Surface-enhanced Raman scattering(SERS) studies using Rhodamine-6G(R6G) as a test molecule indicate that the Au/Ag NRs have excellent sensing potential. The tunable optical properties and strong electromagnetic effect of the Au/Ag NRs, along with their superior SERS signal enhancement, show that Au/Ag NRs are promising for further applications in plasmon sensing and biomolecular detection.

A High-Sensitivity and Broad-Range SPR Glucose Sensor Based on Improved Glucose Sensitive Membranes

An improved glucose sensitive membrane(GSM)is prepared by immobilizing glucose oxidase(GOD)onto a mixture of silica mesocellular foams(SiMCFs)and SiO2 nanoparticles(SiNPs)and then trapping it in a polyvinyl alcohol(PVA)gel.The membrane is coated onto a gold-glass sheet to create a surface plasmon resonance(SPR)sensor.A series of experiments are conducted to determine the optimized parameters of the proposed GSM.For a GSM with a component ratio of SiMCFs:SiNPs=7:3(mass rate),the resonance angle of the sensor decreases from 68.57°to 63.36°,and the average sensitivity is 0.026°/(mg/dL)in a glucose concentration range of 0 mg/dL‒200 mg/dL.For a GSM with a component ratio of SiMCFs:SiNPs=5:5(mass rate),the resonance angle of the sensor decreases from 67.93°to 63.50°,and the sensitivity is 0.028°/(mg/dL)in a glucose concentration range of 0 mg/dL‒160 mg/dL.These data suggest that the sensor proposed in this study is more sensitive and has a broader measurement range compared with those reported in the literature to date.

Resolution Enhancement of Optical Surface Plasmon Resonance Sensor Using Metamaterial

In this paper, we present and discuss a an optical surface plasmon resonance （SPR） path to extend the enhancement of the resolution of sensor. Basically, our approach is to combine bi-metamaterial layers to design the SPR sensor. The calculation shows that the proposed SPR sensor structure has a preference over the conventional SPR sensors and bimetallic SPR sensors since it gives a much sharper reflectance dip and can achieve considerable sensitivity improvement when compared to the recently reported investigations. The effects of the metamaterial permittivity, permeability, and thickness on the reflectance curve are studied. It is also seen that metamaterial layers improve the field of the proposed SPR structure, which may provide a novel tool to significantly enhance the sensitivity and resolution of the sensors.

High sensitivity D-shaped hole fiber temperature sensor based on surface plasmon resonance with liquid filling

A high sensitivity D-shaped hole double-cladding fiber temperature sensor based on surface plasmon resonance(SPR)is designed and investigated by a full-vector finite element method.Within the D-shaped hole doublecladding fiber,the hollow D-section is coated with gold film and then injected in a high thermo-optic coefficient liquid to realize the high temperature sensitivity for the fiber SPR temperature sensor.The numerical simulation results show that the peaking loss of the D-shaped hole double-cladding fiber SPR is hugely influenced by the distance between the D-shaped hole and fiber core and by the thickness of the gold film,but the temperature sensitivity is almost insensitive to the above parameters.When the thermo-optic coefficient is -2.8×10^(-4)∕℃,the thickness of the gold film is 47 nm,and the distance between the D-shaped hole and fiber core is 5μm,the temperature sensitivity of the D-shaped hole fiber SPR sensor can reach to -3.635 nm∕℃.

Concentration sensor with multilayer thin film-coupled surface plasmon resonance

A concentration sensor based on silver(Ag)/silica(SiO2)/zirconium anhydride(ZrO2)multilayer structure is proposed.Two dominant dips can be observed in the reflection spectrum,which correspond to different sensing methods.Firstly,it is demonstrated that the coupling between the surface plasmon polariton(SPP)mode and a planar waveguide mode(WGM)leads to the Fano resonance(FR).The induced bonding hybridized modes have ultra-narrow full wave at half maximum(FWHM)as well as ultra-high quality factors(Q).We can achieve a theoretical value of the refractive index sensitivity 167 times higher than conventional surface plasmon resonance(SPR)sensors with a single metal layer.Secondly,the waveguide coupling mode was examined by measuring angular spectra.A deep and sharp waveguide coupling dip was obtained.The experimental results show that with an increase in the concentration of the fill dielectric material in the surface of the system,the resonance dip exhibits a remarkable red shift,and the measured angular sensitivity is 98.04°/RIU.

Detection of Leptospirosis Bacteria in Rodent Urine by Surface Plasmon Resonance Sensor Using Graphene

In this paper, a graphene-coated surface plasmon resonance sensor is designed for the examination of Rodent urine which is responsible for Leptospirosis bacteria. Rodent urine is considered as sensing medium. Graphene surface is activated by phosphate-buffered saline solution for better attachment of Leptospirosis bacteria on its surface. Oliguria and Polyuria are the Rodent urine with high and low concentrations of Leptospirosis bacteria, respectively. The transfer matrix method is used for the formulation of reflection intensity of p-polarized light. The reflectance curves for angular interrogation are plotted and the results are obtained in terms of sensitivity, detection accuracy, and quality factor. The significantly high sensitivity and detection accuracy for Oliguria distinguishes it from Polyuria having lower sensitivity.

Optical fiber sensor based on the short-range surface plasmon polariton mode

An optical fiber sensor for ultrathin layer sensing based o51 short-range surface plasmon polariton （SRSPP） is proposed, and the sensing characteristics are theoretically analyzed. Simulation results indicate that even for a detecting layer much thinner than the vacuum wavelength, a resolution as high as 3.7×10-6 RIU can be obtained. Moreover, an average ttfickness-detection sensitivity of 6.2 dB/nm is obtained, which enables the sensor to detect the thickness variation of the ultrathin layer up to tens of nanometers. The sensitive region of thickness could be adjusted by tuning the structure parameters.

Visible Light-Illuminated Gold Nanohole Arrays With Tunable On-Chip Plasmonic Sensing Properties

Since the discovery of the extraordinary optical transmission phenomenon,nanohole arrays have attracted much attention and been widely applied in sensing.However,their typical fabrication process,utilizing photolithographic top-down manufacturing technologies,has intrinsic drawbacks including the high costs,time consumption,small footprint,and low throughput.This study presented a low-cost,high-throughput,and scalable method for fabricating centimeter-scale(1×2 cm2)nanohole arrays using the improved nanosphere lithography.The large-scale close-packed polystyrene monolayers obtained by the hemispherical-depression-assisted self-assembly method were employed as colloidal masks for the nanosphere lithography,and the nanohole diameter was tuned from 233 nm to 346 nm with a fixed period of 420 nm via plasma etching.The optical properties and sensing performance of the nanohole arrays were investigated,and two transmission dips were observed due to the resonant coupling of plasmonic modes.Both dips were found to be sensitive to the surrounding environment,and the maximum bulk refractive index sensitivity was up to 162.1 nm/RIU with a 233 nm hole diameter.This study offered a promising approach for fabricating large-scale highly ordered nanohole arrays with various periods and nanohole diameters that could be used for the development of low-cost and high-throughput on-chip plasmonic sensors.