Continuous monitoring of air quality and rapid detection of pollutants are highly desirable in urban planning and development of smart cities. One of the primary greenhouse gases responsible for environmental degradation and respiratory diseases is nitrogen dioxide (NO2). Existing gas sensors for measuring NO2 concentration suffer from drawbacks such as cross-sensitivity, limited range, and short life span. On the other hand, optical sensors, in particular, surface plasmon resonance (SPR) sensors, have emerged as a preferred alternative owing to advantages like high selectivity, immunity to electromagnetic interference, and low response time. In this work, we design and simulate a NO2 sensor based on a glass waveguide coated with a gold film. Surface plasmons are excited at the interface by a 400–500-nm light source, incident at an angle of 43.16°. To enhance the sensitivity, we further coat the waveguide with three layers of carbon-silver (C–Ag) nanodots, which increases the surface plasmon field amplitude by nearly 7 times, in the absence of NO2. When NO2 concentration is varied in the range of 0–200 ppm, a corresponding change is observed in the reflected amplitude. In the absence of the C–Ag nanodots layer, the sensitivity is only 0.00042%/ppm, and on addition of C–Ag nanodots, the sensitivity increases significantly to 0.14235%/ppm which is nearly 343 times higher. These results demonstrate the efficiency of implementing nanodots in SPR sensor to detect and trace concentrations of contaminants in the gas phase.
相似文献This paper deals with the development and analysis of D-Shaped photonic crystal fiber (PCF) biosensors using surface plasmon resonance (SPR). A thin metal layer is deposited on the outer flat surface of the PCF that behaves as the plasmonic material. Analyte is filled in the outermost peripheral region of metal layer. Finite element method (FEM) with perfectly matched layer (PML) is applied to analyze the proposed sensors. Mode analysis is performed on the proposed structures to evaluate various parameters of SPR-based PCF sensors. Three D-shaped PCF structures have been proposed with silver (Ag), gold (Au) and two-half layers of both (Ag-Au) on its flat surface. The first two structures are analyzed to the range of wavelength where the SPR will occur to facilitate understanding of the third structure. It is observed that the structures with one metal have only one sensitive plasmonic peak whereas the structure with two metal layers has two sensitive plasmonic peaks, making it suitable candidate for two-molecule sensing present in a sample analyte. Good sensitivities and resolutions are achieved for both plasmonic peaks.
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下载免费PDF全文 Platinum diselenide (PtSe2), an emerging two-dimensional transition metal dichalcogenide, exhibits thickness-dependent refractive index, and hence, intriguing optical properties. Here, we employ it as a plasmonic sensing substrate to achieve significant enhancement in Goos-Hänchen shift sensitivity. Through systematic optimization of all parameters, four optimum sensing configurations have been achieved at different wavelengths ranging from visible to near-infrared region, where the Goos-Hänchen shift sensitivity receives four times enhancement in comparison with the conventional bare gold sensing substrate. There is a linear range of Goos-Hänchen shift with the tiny change of refractive index for each optimal configuration. The detection limit of the refractive index change can be as low as 5 × 10−7 RIU which is estimated to be lower by 2 orders of magnitude, and the corresponding sensitivity of biomolecules has a 1000-fold increment compared with that of bare gold-based sensors.
相似文献In the present work, a novel surface plasmon resonance (SPR) sensor consisting of the nickel (Ni) film with hybrid structure of blue phosphorene (BlueP)/transition metal dichalcogenides (TMDCs) is reported. By optimizing the thickness of Ni layer and BlueP/TMDCs, the maximum sensitivity with 270°/RIU for the Ni-BlueP/WS2 is achieved. Use of BlueP/TMDCs layer facilitates the sensitivity due to its high electron concentration, high mobility, optical, and electronic properties. Compared with the conventional Ni-based SPR sensor, the sensitivity of the proposed one is enhanced up to ~ 60.7%. We hope that the SPR sensor has potential application prospects in chemical detection, medical diagnostic, optical sensing, etc. due to its high sensitivity.
相似文献Metal-dielectric-graphene hybrid heterostructures based on oxides Al2O3, HfO2, and ZrO2 as well as on complementary metal–oxide–semiconductor compatible dielectric Si3N4 covering plasmonic metals Cu and Ag have been fabricated and studied. We show that the characteristics of these heterostructures are important for surface plasmon resonance biosensing (such as minimum reflectivity, sharp phase changes, resonance full width at half minimum and resonance sensitivity to refractive index unit (RIU) changes) can be significantly improved by adding dielectric/graphene layers. We demonstrate maximum plasmon resonance spectral sensitivity of more than 30,000 nm/RIU for Cu/Al2O3 (ZrO2, Si3N4), Ag/Si3N4 bilayers and Cu/dielectric/graphene three-layers for near-infrared wavelengths. The sensitivities of the fabricated heterostructures were?~?5–8 times higher than those of bare Cu or Ag thin films. We also found that the width of the plasmon resonance reflectivity curves can be reduced by adding dielectric/graphene layers. An unexpected blueshift of the plasmon resonance spectral position was observed after covering noble metals with high-index dielectric/graphene heterostructures. We suggest that the observed blueshift and a large enhancement of surface plasmon resonance sensitivity in metal-dielectric-graphene hybrid heterostructures are produced by stationary surface dipoles which generate a strong electric field concentrated at the very thin top dielectric/graphene layer.
相似文献A self-referencing plasmonic platform is proposed and analyzed. By introducing a thin gold layer below a periodic two-dimensional nano-grating, the structure supports multiple modes including localized surface plasmon resonance (LSPR), surface plasmon resonance (SPR), and Fabry-Perot resonances. These modes get coupled to each other creating multiple Fano resonances. A coupled mode between the LSPR and SPR responses is spatially separated from the sensor surface and is not sensitive to refractive index changes in the surrounding materials or surface attachments. This mode can be used for self-referencing the measurements. In contrast, the LSPR dominant mode shifts in wavelength when the refractive index of the surrounding medium is changed. The proposed structure is easy to fabricate using conventional lithography and electron beam deposition methods. A bulk sensitivity of 429 nm/RIU is achieved. The sensor also has the ability to detect nanometer thick surface attachments on the top of the grating.
相似文献The influence of TiO2 coating on resonant properties of gold nanoisland films deposited on silica substrates was studied numerically and in experiments. The model describing plasmonic properties of a metal truncated nanosphere placed on a substrate and covered by a thin dielectric layer has been developed. The model allows calculating a particle polarizability spectrum and, respectively, its surface plasmon resonance (SPR) wavelength for any given cover thickness, particle radius and truncation parameter, and dielectric functions of the particle, the substrate, the coating layer, and the surrounding medium. Dependence of the SPR position calculated for truncated gold nanospheres has coincided with the measured one for the gold nanoisland films covered with titania of different thicknesses. In the experiments, gold films with thickness of 5 nm were deposited on a silica glass substrate, annealed at 500 °C to form nanoislands of 20 nm in diameter, and covered with amorphous titania layers using atomic layer deposition technique. The resulting structures were characterized with scanning electron microscopy and optical absorption spectroscopy. The measured dependence of the SPR position on titania film thickness corresponded to the one calculated for truncated sphere-shaped nanoparticles with the truncation angle of ~50°. We demonstrated the possibility of tuning the SPR position within ~100 nm range by depositing to 30 nm thick titania layer.
相似文献Extraordinary electrical and optical features of graphene-based materials attract researchers to improve sensing center of different sensors using them. In this research, the effects of sensing molecules on electro-optical features of graphene-based sensors are modeled. The adsorption effect on the Hamiltonian of the system based on tight-binding model is explored, and also the system band structure is investigated analytically. Then, refractive index deviations based on band gap variations are discovered which are used in response modeling of a graphene-based surface plasmon resonance (SPR) sensor.
相似文献The performance of surface plasmon resonance (SPR) sensors has great dependence on its plasmonic material’s frequency response, which is described by the complex dielectric function. Through history, researchers developed and enhanced mathematical models to accurately describe the material dielectric function. Although many papers compared the accuracy of different dielectric function models and stated its limitations, none of it addressed the effect of dielectric function model on the SPR sensor’s characteristics. In this paper, we investigated the performance of the three most used dielectric function models (Drude, Lorentz-Drude, and Brendel-Bormann) and their effect on the theoretically obtained sensor parameters when used in a gold SPR sensor’s model and validated it with the experimentally measured dielectric function. The result showed that using less accurate dielectric function’s model has a drastic effect on the theoretically obtained sensor’s parameters. Among the three models, the widely used Drude model was not the most accurate; alternatively, Brendel-Bormann model was the most accurate.
相似文献In this paper, we demonstrate a novel salinity sensor based on Tamm-plasmon-polariton (TPP), comprising different shapes of Bragg reflector (ordinary, texturing, and sawtooth) and metallic layer. The finite element method is used to study the considered structure and sensing performance by using the COMSOL multiphysics simulation procedure. Here, we study the effect of surface morphology on the sensitivity; firstly, in the case of one-dimensional photonic crystal-centered defect, it harms the sensitivity; secondly, texturing and sawtooth in the case of Tamm resonance increases the sensitivity, as for texturing the surface, the sensitivity quality factor (Q)?=?236 and figure of merit (FOM)?=?170. For sawtooth surfaces, Q?=?272.4, and FOM?=?199. The consequences of structural parameters on the efficiency of sensing are studied, and new procedures are proposed to enhance TPP-based sensors. A simple and functional alternative to conventional salinity sensors may be the proposed solution.
相似文献We demonstrate that a designed bimetallic chip is capable of improving the performance of a surface plasmon resonance (SPR) sensor based on angular interrogation. Through a numerical simulation and a refractometry experiment, we prove that this bimetallic chip can effectively reduce the noise level by about a factor of 2 compared to the traditional SPR sensors that only use a single gold film. The bimetallic chip presents a lower refractive index resolution of 5.3 × 10−7 refractive index units. In addition, the enhancement of the electric field intensity at the surface of the configuration by a factor of 2 makes it possible to have a high sensitivity in a larger region, which promotes the biosensing applications of the chip. Through a simple and novel method for the detection of cadmium ions (Cd2+) based on the bimetallic configuration, a detection level for Cd2+ (0.01 μM or 1.12 ppb) can be realized, which compares favorably with similar studies.
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