Showing papers in "Plasmonics in 2017"

Highly Sensitive Surface Plasmon Resonance Based D-Shaped Photonic Crystal Fiber Refractive Index Sensor

Abstract: In this article, a D-shaped photonic crystal fiber based surface plasmon resonance sensor is proposed for refractive index sensing. Surface plasmon resonance effect between surface plasmon polariton modes and fiber core modes of the designed D-shaped photonic crystal fiber is used to measure the refractive index of the analyte. By using finite element method, the sensing properties of the proposed sensor are investigated, and a very high average sensitivity of 7700 nm/RIU with the resolution of 1.30 × 10−5 RIU is obtained for the analyte of different refractive indices varies from 1.43 to 1.46. In the proposed sensor, the analyte and coating of gold are placed on the plane surface of the photonic crystal fiber, hence there is no necessity of the filling of voids, thus it is gentle to apply and easy to use.

Analysis of Graphene-Based Photonic Crystal Fiber Sensor Using Birefringence and Surface Plasmon Resonance

Abstract: We present and numerically characterize a photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor. By adjusting the air hole sizes of the PCF, the effective refractive index (RI) of core-guided mode can be tuned effectively and the sensor exhibits strong birefringence. Alternate holes coated with graphene-Ag bimetallic layers in the second layer are used as analyte channels, which can avoid adjacent interference and improve the signal to noise ratio (SNR). The graphene’s good features can not only solve the problem of silver oxidation but also increase the absorption of molecules. We theoretically analyze the influence of the air hole sizes of the PCF and the thicknesses of graphene layer and Ag layer on the performance of the designed sensor using wavelength and amplitude interrogations. The wavelength sensitivity we obtained is as high as 2520 nm/RIU with the resolution of 3.97 × 10−5 RIU, which can provide a reference for developing a high-sensitivity, real-time, fast-response, and distributed SPR sensor.

Review of Metasurface Plasmonic Structural Color

Abstract: The environmental concerns in the current century is not only limited to the polluting effect of the fossil fuel consumption but also the recycling challenges of waste turns to be a substantial challenges of the industry. Recycling of colored discarded materials is very difficult because of the problems in relation to the dissociation of diverse chemical compounds present in the colorant agents. Single or double component materials which could create various colors by geometrical changes can be a great solution to the mentioned limitations. Metasurfaces’ and metamaterials’ structural color therefore draws attention as they enable generation of vivid colors only by geometrical arrangement of metals which not only ease the recycling but at the same time enhance the mechanical stability of the colors. In this review, the progress in the field of plasmonic metasurface- and metamaterial-based structural colors is reviewed.

Polarization Insensitive and Broadband Terahertz Absorber Using Graphene Disks

Abstract: We demonstrate design and characterization of a polarization-independent ultra-broadband absorber of light consisting of periodic array of graphene disks on top of a lossless quarter-wavelength dielectric spacer placed on a metallic reflector. The absorber is duly designed based on impedance matching concept by proposing a fully analytical circuit model resulting in a normalized bandwidth of 100 % in the terahertz regime.

Highly Sensitive SPR Sensor Based on D-shaped Photonic Crystal Fiber Coated with Indium Tin Oxide at Near-Infrared Wavelength

Abstract: A surface plasmon resonance (SPR) sensor based on D-shaped photonic crystal fiber (PCF) coated with indium tin oxide (ITO) film is proposed and numerically investigated. Thanks to the adjustable complex refractive index of ITO, the sensor can be operated in the near-infrared (NIR) region. The wavelength sensitivity, amplitude sensitivity, and phase sensitivity are investigated with different fiber structure parameters. Simulation results show that ∼6000 nm/refractive index unit (RIU), ∼148/RIU, and ∼1.2 × 106 deg/RIU/cm sensitivity can be achieved for wavelength interrogation, amplitude interrogation, and phase interrogation, respectively, when the environment refractive index varies between 1.30 and 1.31. It is noted that the wavelength sensitivity and phase sensitivity are more pronounced with larger refractive index. The proposed SPR sensor can be used in various applications, including medicine, environment, and large-scale targets detection.

Analogue Electromagnetically Induced Transparency Based on Low-loss Metamaterial and its Application in Nanosensor and Slow-light Device

Abstract: In this paper, we demonstrated a low-loss and high-transmission analogy of electromagnetically induced transparency based on all-dieletric metasurface. The metamaterial unit cell structure is composed of two mutually perpendicular silicon nanoscale bars. Under the joint effects of the neighboring meta-atoms’ coherent interaction and significant low absorption loss, the transmission and the Q-factor can reach up to 93 % and 139, respectively. Moreover, we use the coupled harmonic oscillator model to analyze the near field interaction between the two elements in the electromagnetically induced transparency (EIT) metamaterial unit cell qualitatively and the effects of parameters on EIT. The figure-of-merit of 42 and the group delay of 0.65 ps are obtained. These characteristics make the metamaterial structure with potential to apply for ultrafast switches, sensor, and slow-light devices.

Ultra-Broadband Linear Polarization Conversion via Diode-Like Asymmetric Transmission with Composite Metamaterial for Terahertz Waves

Abstract: In this paper, a tri-layer metamaterial composed of a split-disk structure array sandwiched with two layers of twisted sub-wavelength metal grating is proposed and investigated numerically in terahertz region. The numerical results exhibit that linear polarization conversion via diode-like asymmetric transmission for terahertz waves within ultra-broadband frequency range is achieved due to Fabry-Perot-like resonance. In our design, the conversion polarization transmission coefficient for normal incidence is greater than 90 % in the range of 0.23–1.17 THz, equivalent to 134.3 % relative bandwidth. The physical mechanism of the broadband linear polarization conversion effect is further illustrated by simulated electrical field distributions.

A Highly Sensitive Dual-Core Photonic Crystal Fiber Based on a Surface Plasmon Resonance Biosensor with Silver-Graphene Layer

Abstract: A highly sensitive dual-core photonic crystal fiber based on a surface plasmon resonance (PCF-SPR) biosensor with a silver-graphene layer is described. The silver layer with a graphene coating not only prevents oxidation of the silver layer but also can improve the silver sensing performance due to the large surface-to-volume ratio of graphene. The dual-core PCF-SPR biosensor is numerically analyzed by the finite-element method (FEM). An average spectral sensitivity of 4350 nm/refractive index unit (RIU) in the sensing range between 1.39 and 1.42 and maximum spectral sensitivity of 10,000 nm/RIU in the sensing range between 1.43 and 1.46 are obtained, corresponding to a high resolution of 1 × 10−6 RIU as a biosensor. Our analysis shows that the optical spectra of the PCF-SPR biosensor can be optimized by varying the structural parameters of the structure, suggesting promising applications in biological and biochemical detection.

Utilizing the Metallic Nano-Rods in Hexagonal Configuration to Enhance Sensitivity of the Plasmonic Racetrack Resonator in Sensing Application

Abstract: A high sensitive plasmonic refractive index sensor based on metal-insulator-metal (MIM) waveguides with embedding metallic nano-rods in racetrack resonator has been proposed. The refractive index changes of the dielectric material inside the resonator together with temperature changes can be acquired from the detection of the resonance wavelength, based on their linear relationship. With optimum design and considering a tradeoff among detected power, structure size, and sensitivity, the finite difference time domain simulations show that the refractive index and temperature sensitivity values can be obtained as high as 2610 nm per refractive index unit (RIU) and 1.03 nm/°C, respectively. In addition, resonance wavelengths of resonator are obtained experimentally by using the resonant conditions. The effects of nano-rods radius and refractive index of racetrack resonator are studied on the sensing spectra, as well. The proposed structure with such high sensitivity will be useful in optical communications that can provide a new possibility for designing compact and high-performance plasmonic devices.

Extra-broad Photonic Crystal Fiber Refractive Index Sensor Based on Surface Plasmon Resonance

Abstract: We propose and investigate a photonic crystal fiber (PCF) refractive index sensor with triangular lattice and four large-size channels based on surface plasmon resonance. In such sensor, two gold wires obtained by chemical reaction are filled in two air holes between the upper and lower channels. Numerical results show that the refractive indexes of the analytes can be detected from 1.30 to 1.79. It’s a very broad detection range that is rarely seen in the field of photonic crystal fiber sensor based on surface plasmon resonance. The average sensitivity of this photonic crystal fiber could be 100 nm/refractive index unit (RIU) in the dynamic index range from 1.30 to 1.63. In the range from 1.63 to 1.79, the highest sensitivity could reach to 3233 nm/RIU. The ability to integrate four large-size microfluidic channels for efficient analyte flow in is attractive for the development of integrated highly sensitive PCF-SPR sensors.

Structural, Optical and Plasmonic Properties of Ag-TiO2 Hybrid Plasmonic Nanostructures with Enhanced Photocatalytic Activity

Abstract: Hybrid plasmonic nanostructures consisting of Ag nanoparticles decorated TiO2 nanorods with highly enhanced photocatalytic activity were synthesized by a facile wet chemical method. The structural, optical, plasmonic and photocatalytic properties of the synthesized Ag-TiO2 hybrid nanostructures were well characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), Raman spectroscopy, photoluminescence spectroscopy (PL) and UV-visible absorption spectroscopy. The photocatalytic activities of the as-synthesized Ag-TiO2 hybrid nanostructures were evaluated by studying sun light-driven photocatalytic degradation of methylene blue (MB) and methyl orange (MO) dyes in water. The results showed that Ag-TiO2 hybrid nanostructures exhibit highly enhanced photocatalytic activity towards degradation of MB and MO dyes and the photocatalytic efficiency increased with increase in Ag nanoparticle loading. The mechanism underlying the highly enhanced photocatalytic activity of Ag-TiO2 nanohybrids is proposed. We attribute the observed enhanced photocatalytic activity of Ag-TiO2 hybrid nanostructures to the efficient separation of photogenerated charge carriers in TiO2 due to the electron scavenging action of Ag nanoparticles and the improved sun light utilization by the plasmonic nanohybrids originating from the surface plasmon resonance (SPR) absorption of Ag nanoparticles.

High Sensitivity Nanoplasmonic Sensor Based on Plasmon-Induced Transparency in a Graphene Nanoribbon Waveguide Coupled with Detuned Graphene Square-Nanoring Resonators

Abstract: A novel nanoscale structure for high sensitivity sensing which consists of a graphene nanoribbon waveguide coupled with detuned graphene square-nanoring resonators (GSNR) based on edge mode is investigated in detail. By altering the Fermi energy level of the graphene, the plasmon-induced transparency (PIT) window from the destructive interference between a radiative square-nanoring resonator and a dark square-nanoring resonator can be easily tailored. The coupled mode theory (CMT) is used to show that the theoretical results agree well with the finite difference time domain (FDTD) simulations. This nanosensor yields a ultrahigh sensitivity of ∼2600 nm/refractive index unit (RIU) and a figure of merit (FOM) of ∼54 in the mid-infrared (MIR) spectrum. The revealed results indicate that the Fermi energy level of the graphene and the coupling distance play important roles in optimizing the sensing properties. Our proposed structure exerts a peculiar fascination on the realization of ultra-compact graphene plasmonic nanosensor in the future.

Electromagnetically Induced Transparency and Refractive Index Sensing for a Plasmonic Waveguide with a Stub Coupled Ring Resonator

Abstract: A plasmonic refractive index sensor based on electromagnetically induced transparency (EIT) composed of a metal-insulator-metal (MIM) waveguide with stub resonators and a ring resonator is presented. The transmission properties and the refractive index sensitivity are numerically studied with the finite element method (FEM). The results revealed an EIT-like transmission spectrum with an asymmetric line profile and a refractive index sensitivity of 1057 nm/RIU are obtained. The coupled mode theory (CMT) based on transmission line theory is adopted to illustrate the EIT-like phenomenon. Multiple EIT-like peaks are observed in the transmission spectrum of the derived structures based on the MIM waveguide with stub resonator coupled ring resonator. To analyze the multiple EIT-like modes of the derived structures, the H z field distribution is calculated. In addition, the effect of the structural parameters on the EIT-like effect is also studied. These results provide a new method for the dynamic control of light in the nanoscale.

One Dimensional Plasmonic Grating: High Sensitive Biosensor

Abstract: We report a simple 1D grating device fabrication on ∼50 nm gold (Au) film deposited on glass, which is employed as a high performance refractive index (RI) sensor by exploiting the surface plasmon polaritons (SPP) excited by the grating device along the Au/analyte interface. A finite element analysis (FEA) method is employed to maximize the sensitivity of the sensor for a fixed period and thickness of a gold film and its close correspondence with experiment has given the insight for high sensitivity and enhanced transmission. Significantly, in the context of economic design and performance, it is shown that an optimally designed and fabricated 1D grating can be as sensitive as 524 nm/RIU (linearity RI = 1.33303 to 1.47399), which is remarkably higher than existing reports operating in a similar wavelength region.

Achieving a High Q-Factor and Tunable Slow-Light via Classical Electromagnetically Induced Transparency (Cl-EIT) in Metamaterials

Abstract: We report on our numerical work concerning a 3D planar nano-structure metamaterial exhibiting classical electromagnetically induced transparency (Cl-EIT). The interaction between two different plasmonic modes of the unit cell, induced directly or indirectly by the incident electromagnetic wave, leads to a transparent window, resembling the Cl-EIT. Their interactions and coupling between plasmonic modes are investigated in detail by analyzing magnetic field distributions and spectral responses. Simply by introducing of symmetry broken of the proposed nano-structure, the Cl-EIT can be dynamically tuned. At one special asymmetric case, a sharp transparency window with the bandwidth of about 2.96 nm (corresponding to 0.6 THz in frequency regime) is obtained at 246.3 THz (corresponding to 1.218 μm). The corresponding quality factor (Q-factor) is 411. Also, we show that the Cl-EIT frequency position depended very sensitively on the used metal in the metamaterial. Furthermore, we demonstrate numerically that tunable slow light can be realized in our planar nano-structure metamaterial with the unit cell composed of dark and bright plasmonic modes in a broad terahertz regime. It is demonstrated that the increased Q-factor leads to large group index (of the order of 620), which is promising for efficient plasmonic sensing, optical switching, and slow-light devices design.

Plasmonic Perovskite Solar Cells Utilizing Au@SiO2 Core-Shell Nanoparticles

Abstract: The role of Au@SiO2 core-shell nanoparticles on optical properties of perovskite solar cells has been explored using both the theoretical computations and the experiments. A quasi-static model is used to study the surface plasmon resonances (SPRs) of Au@SiO2 core-shell nanospheres. Au@SiO2 core-shell nanoparticles, with varying shell thickness and core radius, were assumed to be embedded in methylammonium lead triiodide (CH3NH3PbI3) perovskite active layer. Enhanced absorption in the active layer is obtained due to the near-field plasmonic effect of the embedded core-shell nanoparticles. Theoretical modelling shows that a shell thickness of 1 nm and core diameter of 20 nm provide absorption enhancement in the orange-red region of the electromagnetic spectrum. Experiments performed using ∼20-nm-sized Au@SiO2 core-shell nanoparticles (with a shell thickness of ∼1 nm) clearly demonstrate the enhanced absorption and the resulting enhancement in photocurrent due to the plasmonic effects. An efficiency enhancement of over 18 % is obtained for the best plasmonic perovskite solar cell containing Au@SiO2 nanoparticles in Au@SiO2-TiO2 weight ratio of ∼1 %. Incident photon-to-current conversion efficiency (IPCE) data also showed enhancement in photocurrent for the plasmonic device. The quasi-static modelling approach provides a good correlation between theory and experiment.

Design of One-Bit Magnitude Comparator Using Nonlinear Plasmonic Waveguide

Abstract: The effective optical switching property of Mach–Zehnder interferometer (MZI) utilizing optical Kerr effect has been precisely reported suitably assisted with an analytical approach in this paper. MZI plays the role of the fundamental building block in the designing of intricate combinational circuit by employing Kerr effect. This paper constitutes ultra-compact design of one-bit magnitude comparator along with its mathematical analysis. The analysis of device is justified through MATLAB and finite-difference time-domain (FDTD) method.

Tailoring Plasmon Lifetime in Suspended Nanoantenna Arrays for High-Performance Plasmon Sensing

Abstract: We demonstrate significantly longer plasmon lifetime and stronger electric field enhancement by lifting the nanoantenna arrays above the substrate by dielectric nanopillars. The role of the pillar is to offer a more homogeneous dielectric background allowing stronger diffraction coupling among plasmonic nanoantennas leading to a Fanolike asymmetric lineshape. It is found that the electric fields around the nanoantennas can be greatly enhanced when the Fanolike resonance is excited, and a 4.2 times enhancement is achieved compared with the pure resonance in individual nanoantennas. Furthermore, only a collective surface mode with its electric fields of the same direction as the induced electric moment in the nanoantennas could mediate the excitation of such a Fanolike resonance. More importantly, the sensitivity and the figure of merit (FOM) of this plasmonic structure can reach as high as 900 nm/RIU and 53, respectively. Our study offers a new, simple, and efficient way to design the plasmonic systems with desired electric field enhancement and spectral lineshape for different applications.

Fano Resonance Based on End-Coupled Cascaded-Ring MIM Waveguides Structure

Abstract: Though adding a groove to a plasmonic end-coupled perfect ring (PR) resonator, two additional resonance modes, which can be controlled by the length of the groove, will arise in this proposed ring-groove (RG) joint metal-insulator-metal (MIM) waveguide. By further cascading, the PR resonator and the RG joint resonator, single and dual Fano resonances with asymmetric line shapes are obtained due to the interference effects between the dark modes and the bright modes. High figure of merit and high refractive-index sensitivity are achieved, and thus this structure is suitable for the biochemistry sensing area. Interestingly, normal and abnormal dispersions are also investigated for the Fano peaks and dips, respectively. The performances of the proposed structure are investigated by using the finite-difference time-domain method.

Ultra-broadband Polarization-Independent Wide-Angle THz Absorber Based on Plasmonic Resonances in Semiconductor Square Nut-Shaped Metamaterials

Abstract: Metamaterials are considered to be a promising candidate of making THz absorber for function devices to replace natural materials. Based on geometry evolution, the electromagnetic characteristics of metamaterials can be tailed to enhance the weak THz response of natural materials. Appropriate constituent selection and inhomogeneous geometry constructions are proved to be effective to extend the narrow frequency band of traditional metal resonator-based metamaterial absorbers. In this work, doped silicon was used as the only constituent, and the inhomogeneous geometry was designed in a very simple way (so-called square nut structure) with the assistant of transmission line theory and geometry evolution methodology. Ultra-broadband absorption from 1.6 to 5 THz was verified numerically with an efficiency over 90 %. Various plasmonic resonance modes including surface plasmon polaritons (SPP) together with local surface plasmonic resonance (LSPR) tuned by the inhomogeneous structures and cavities contributed to this broadband absorption. Further working with this geometrical variation concept, our “wheel hub-like” structure achieved ultra-broadband absorption from 0.98 to 5 THz. Our investigations could provide an alternative design methodology for the design of metamaterial THz absorbers.

Tunable Salisbury Screen Absorber Using Square Lattice of Plasmonic Nanodisk

Abstract: We propose a novel polarization independent Salisbury screen absorber to provide tunable resonant absorption at terahertz (THz) frequencies. The Salisbury screen absorber is designed by using a planar array of thin gold nanodisks arranged in a square lattice. Certain configurations of Salisbury screen have multiple distinctive absorption bands that support near-unity/FWHM absorption bandwidth reaching 36 THz/169 THz, respectively. Moreover, the absorption bandwidth depends upon the optical thickness of the dielectric spacer between the metasurface and the metallic ground plane. The proposed tunable Salisbury screen absorber can find practical applications in photonic detection, imaging, sensing, and solar cells at optical frequencies.

Design of a Single-Polarization Single-Mode Photonic Crystal Fiber Filter Based on Surface Plasmon Resonance

Abstract: We design a single-polarization single-mode photonic crystal fiber filter based on surface plasmon resonance The finite element method is employed to evaluate the characteristics of the filter The proposed fiber is devised such that there is a great discrepant confinement loss between two polarizations of x and y by varying two air holes in the cladding region, which is composed of hexagonal structural air holes in pure silica selectively filling with gold wires Numerical simulations show that single-polarization single-mode operation waveband can be tuned by adjusting the parameters of the photonic crystal fiber The confinement losses of the unwanted polarization can reach to 12610 and 32630 dB/cm in the wavelengths of 131 and 155 μm, while the corresponding confinement losses of the wanted polarized mode are only 008 and 120 dB/cm, respectively Furthermore, the crosstalk can come to a maximum of 12034 and 31041 dB in the two communication bands The bandwidths of the fiber designed for 131 and 155 μm are, respectively, 20 and 60 nm, which may be found useful applications for fiber polarizer

Single-Patterned Metamaterial Structure Enabling Multi-band Perfect Absorption

Abstract: Multi-band or broadband perfect metamaterial absorbers, based on coplanar super-unit structure or multiple vertically stacked layers, have received intense attention because of their potential for practical applications. The resonance mechanism of them usually only utilizes the overlapping of the fundamental resonance of the different-sized patterns, and neglects the high-order resonance of the structure, and thus making the proposed structures quite troublesome to be fabricated and the mechanism of the current demonstrated absorbers lack of novelty. In this paper, a simple design of dual-band terahertz absorber consisted of only a traditional square metallic patch and a dielectric layer on top of a continuous ground plane is presented. Simulation results show that the single resonant structure has two resonance absorption peaks, which are both average over 99.5 %. The mechanism of the dual-band absorber is due to the overlapping of the fundamental mode and three-order response of the patterned structure, which is totally different from previous reports that only combining the fundamental resonances of the different-shaped complex structures to obtain the dual-band response. Furthermore, the proposed single-patterned structure can be used to extend the number of the absorption peaks (for example, triple-band absorber) by combining one more resonance (the five-order response). The proposed absorbers with the simple structure design have potential applications in many areas, such as detection, sensing, and selective thermal emitters.

A High Performance Plasmonic Sensor Based on Metal-Insulator-Metal Waveguide Coupled with a Double-Cavity Structure

Abstract: A high performance plasmonic sensor based on a metal-insulator-metal (MIM) waveguide coupled with a double-cavity structure consisting of a side-coupled rectangular cavity and a disk cavity is proposed The transmission characteristics of the rectangular cavity and disk cavity are analyzed theoretically and the improvements of performance for the double-cavity structure compared with a single cavity are studied The influence of structural parameters on the transmission spectra and sensing performance are investigated in detail A sensitivity of 1136 nm/RIU with a high figure of merit of 51,275 can be achieved at the resonant wavelength of 11485 nm Due to the high performance and easy fabrication, the proposed structure may be applied in integrated optical circuits and on-chip nanosensors

Frequency-Tunable Mid-Infrared Cross Polarization Converters Based on Graphene Metasurface

Abstract: We have proposed two designs of graphene-enabled cross polarization converters, which are capable of high-efficiency polarization conversion rate and can work equally well for a wide range of incident wave angles. The first type is carefully constructed by an ellipse-shaped graphene sheet printed on a dielectric material backed up by a gold ground plane, while the second one comprises a graphene ring embedded an ellipse resonator. Numerical results demonstrate that the polarization conversion rate of the first polarizer reaches 99.38 % at 22.541 THz when the Fermi energy is fixed at 0.9 eV. The second one can simultaneously work at two frequencies with its polarization conversion rate being 96.74 and 95.88 %, respectively. Therefore, for two devices, the incident linearly polarized beams are almost completely rotated to its orthogonal counterpart after reflection in the mid-infrared spectral range. More importantly, the cross polarization amplitude and resonant frequencies can be dynamically tuned by shifting the Fermi energy without changing the nanostructure, which will exhibit enormous potential applications in photonics field.

Multi-Band Asymmetric Transmission and 90° Polarization Rotator Based on Bi-Layered Metasurface with F-Shaped Structure

Abstract: In this paper, a chiral metamaterial consisting of bi-layered metasurface with double F-shaped resonators is investigated. We experimentally demonstrate that this new structure can realize multi-band asymmetric transmission of a linearly polarized wave in the microwave region. The simulated results also show that the structure can achieve multi-band 90° polarization rotator for a y-polarized wave. The mechanisms of coupling modes are analyzed by the current distribution at different resonant frequencies, which indicates that the cross-polarized transmission is due to both the electric coupling and the magnetic coupling. Furthermore, the polarization conversion ratios (PCRs) with more than 90 % conversion efficiency of x-polarized and y-polarized waves are also studied based on the optical activity and electric field distributions.

Graphene/Graphene Oxide-Based Ultrasensitive Surface Plasmon Resonance Biosensor

Abstract: Surface plasmon resonance (SPR)-based biosensing is an accurate and sensitive technique used to evaluate the biomolecular interactions in real time in a label-free environment. Several new approaches have been proposed to improve the sensitivity of SPR sensors. The development of sensing surfaces can significantly improve the performance of biosensors; graphene and graphene oxide (GO) offer several advantages due to their extraordinary optical and structural properties. In this paper, the SPR biosensor structure based on graphene and GO linking layers are suggested. For proposed configurations, the features and characteristics such as reflectivity and sensitivity using the finite element analysis (FEA) model are discussed and compared with results from N-layer model. The effect of cap layer thickness in the sensitivity of the SPR biosensor has been calculated. Computational results show that the proposed graphene and GO-based SPR biosensor have more than two and four times greater sensitivity than the conventional gold film-based SPR sensor respectively due to their better adsorption of biomolecules.

An Ultrasensitive and Multispectral Refractive Index Sensor Design Based on Quad-Supercell Metamaterials

Abstract: Plasmonic metamaterials support the localized surface plasmon resonance (LSPR), which is sensitive to the change in the dielectric environment and highly desirable for ultrasensitive biochemical sensing. In this work, a novel design of supercell metamaterials of four mutually rotating split ring resonators (SRRs) is proposed, where simultaneous excitations of odd ( N = 1 and N = 3) and even ( N = 2) resonance modes are realized due to additional asymmetry from the rotation and show insensitivity to two orthogonal polarizations. The full utilization of these three resonance dips show bright prospects for multispectral application. As a refractive index (RI) sensor, ultrahigh sensitivities ∼1000 nm/RIU for LC mode ( N = 1) and ∼500 nm/RIU for plasmon mode ( N = 2) are obtained in the near infrared (NIR) spectrum.

Spectral Phase Shift of Surface Plasmon Resonance in the Kretschmann Configuration: Theory and Experiment

Abstract: The spectral phase shift of surface plasmon resonance (SPR) in the Kretschmann configuration is modeled for aqueous solutions of NaCl (analytes) and an SPR structure consisting of gold and chromium layers deposited on an SF10 glass slide. Using the material dispersion of the SPR structure and the analyte, the SPR phase shift, its spectral derivative, and the spectral dependence of the ratio of the reflectances of p- and s-polarized waves are determined for aqueous solutions of NaCl when the concentration of NaCl in water and the refractive index range from 0 to 10 weight percent (wt%) and from 1.3334 to 1.3515 RIU, respectively. In addition, theoretical modeling is accompanied by experiment and the position of a sharp maximum in the measured spectral derivative of the SPR phase shift changes in a range from 596 to 626 nm. From the measurements, a sensitivity to concentration of 3.83 nm/wt% and a detection limit of 7.3 × 10−7 RIU at a wavelength of 612.36 nm are obtained, and very good agreement between theory and experiment is confirmed.

Influence of Dielectric Coating on Performance of Surface Plasmon Resonance Sensor

Abstract: In the present study, the nature of dielectric layer above metal layer in surface plasmon resonance sensor is investigated. The performance-defining parameters, i.e., shift in resonance angle, half width at half maximum, and minimum reflection intensity, are investigated according to the variation of refractive index (real as well as imaginary) of dielectric layer. Moreover, these parameters are investigated according to the thickness variation of the dielectric layer at different purely real as well as complex refractive index of the dielectric layer.