Highly Sensitive Plasmonic Refractive Index Sensor Based on Dual D-Shaped Photonic Crystal Fiber with Aluminum Nitride-Silver Films

A dual-core and dual D-shaped photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor with silver and aluminum nitride (AlN) films is designed. The distribution characteristics of the electromagnetic fields of core and plasmon modes, as well as the sensing properties, are numerically studied by finite element method (FEM). The structure parameters of the designed sensor are optimized by the optical loss spectrum. The results show the resonance wavelength variation of 489 nm for the refractive index (RI) range of 1.36?~?1.42. In addition, a maximum wavelength sensitivity of 13,400 nm/RIU with the corresponding RI resolution of 7.46?×?10^?6 RIU is obtained in the RI range of 1.41?~?1.42. The proposed sensor with the merits of high sensitivity, low cost, and simple structure has a wide application in the fields of RI sensing, such as hazardous gas detection, environmental monitoring, and biochemical analysis.

     

Ultra-narrow-band Infrared Absorbers Based on Surface Plasmon Resonance

Due to the advantage of improving the sensing performance, narrow-band metamaterial perfect absorbers (MPAs) have attracted much attention in the sensor field. Here, we propose an ultra-narrow-band infrared absorber (UNBIRA) based on localized surface plasmon resonance. The peak absorption of the UNBIRA exceeds 99% with the full width at half maximum (FWHM) of 1.94 nm and 6.32 nm for transverse electric (TE) wave and transverse magnetic (TM) wave in 1.5–1.8 μm. The corresponding Q-factors for TE wave and TM wave are 817 and 266, respectively. When used as an infrared refractive index sensor, the sensitivity of UNBIRA is as high as 1632.5 nm/RIU for TE wave and 1647.5 nm/RIU for TM wave. Accordingly, the figure of merits (FOMs) of 816.2/RIU for TE wave and 260.7/RIU for TM wave are achieved. This UNBIRA possesses a simple geometry structure and an excellent sensing performance, implying a great potential for application of ultra-narrow infrared sensing or detecting.

     

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

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.

     

A Novel Diamond Ring Fiber-Based Surface Plasmon Resonance Sensor

We propose a highly sensitive novel diamond ring fiber (DRF)-based surface plasmon resonance (SPR) sensor for refractive index sensing. Chemically active plasmonic material (gold) layer is coated inside the large cavity of DRF, and the analyte is infiltrated directly through the fiber instead of selective infiltration. The light guiding properties and sensing performances are numerically investigated using the finite element method (FEM). The proposed sensor shows a maximum wavelength and amplitude interrogation sensitivity of 6000 nm/RIU and 508 RIU^?1, respectively, over the refractive index range of 1.33–1.39. Additionally, it also shows a sensor resolution of 1.67 × 10^?5 and 1.97 × 10^?5 RIU by following the wavelength and amplitude interrogation methods, respectively. The proposed diamond ring fiber has been fabricated following the standard stack-and-draw method to show the feasibility of the proposed sensor. Due to fabrication feasibility and promising results, the proposed DRF SPR sensor can be an effective tool in biochemical and biological analyte detection.     

Tamm Plasmon Polariton as Refractive Index Sensor Excited by Gyroid Metals/Porous Ta2O5 Photonic Crystal

In this paper, a novel refractive index sensor in terahertz region is proposed. The proposed structure is prism/(sample/porousTa₂O₅)¹⁵/sample/gyroid metal/substrate. The sensor is based on the Tamm plasmon polariton at the interface between porous one-dimensional photonic crystal and gyroidal metal. The gyroidal metal has been used as an alternative metal and its refraction index can be tuned by the gyroid parameters. The effects of the metal volume fraction and sample refractive index on the performance are studied to improve the ability of the sensor. The proposed sensor achieves high sensitivity of 6.7 THz/RIU, a high figure of merit 6*10³ RIU^?1, a high-quality factor of 3*10³, and a low detection limit of 9*10^?6 RIU. The proposed device can be a good candidate for fabricating gyroid metal and porous material-based biosensors, active optoelectronic and polaritonic devices.

     

High Sensitivity in Ni-Based SPR Sensor of Blue Phosphorene/Transition Metal Dichalcogenides Hybrid Nanostructure

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.

     

A Speckle-Free Angular Interrogation SPR Imaging Sensor Based on Galvanometer Scan and Laser Excitation

A speckle-free fast angular interrogation surface plasmon resonance imaging (SPRi) sensor based on a diode-pumped all-solid-state laser and galvanometer is reported in this work. A bidirectional scan using a galvanometer realizes the fast scanning of the incidence angle. The experimental results showed that the time needed for completing an SPR dip measurement was decreased to 0.5 s. And through cascading an immovable diffuser and two diffusers rotating in opposite directions, laser speckle was eliminated. The dynamic detection range and the sensitivity reached 4.6 × 10⁻² and 1.52 × 10⁻⁶ refractive index unit (RIU), respectively, in a 2D array sensor when the angle scanning range was set as 7.5°. More importantly, the results demonstrated that the angular interrogation SPR imaging sensor scheme had the capability to perform fast and high-throughput detection of biomolecular interactions at 2D sensor arrays.

     

A Polarization-independent SPR Sensor Based on Photonic Crystal Fiber for Low RI Detection

A surface plasmon resonance (SPR) sensor based on a photonic crystal fiber (PCF) is proposed for low refractive index (RI) detection. The core of PCF is formed by two-layer air walls and either layer is composed of six identical sector rings with negative curvature. Plasmonic material gold (Au) is coated on the external cladding surface. Finite element method (FEM) is applied to investigate the performance of the SPR sensor. Results show that the sensor is independent of polarization due to the coincident coupling properties of the two polarized modes. Additionally, in low RI ranging from 1.20 to 1.33, the sensor keeps a high spectral sensitivity with an average value of 7738 nm/RIU. When RI varies from 1.32 to 1.33, the resolution reaches to its maximum of 8.3 × 10⁻⁶. The proposed sensor shows much significance in low RI detection, which is promising in real-time measurement for medical, water pollution, and humidity.

     

Compact and low-cost biosensor based on novel approach to spectroscopy of surface plasmons

A high-performance surface plasmon resonance (SPR) sensor based on a novel approach to spectroscopy of surface plasmons is reported. This approach employs a special diffraction grating structure (referred to as surface plasmon resonance coupler and disperser, SPRCD) which simultaneously couples light into a surface plasmon and disperses the diffracted light for spectral readout of SPR signal. The developed SPRCD sensor consists of a miniature cartridge integrating the diffraction grating and microfluidics and a compact optical system which simultaneously acquires data from four independent sensing channels in the cartridge. It is demonstrated that the SPRCD sensor is able to measure bulk refractive index changes as small as 3 × 10⁻⁷ RIU (refractive index units) and to detect short oligonucleotides in concentrations down to 200 pM.     

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

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.     

Metallic Grating-Assisted Fiber Optic SPR Sensor with Extreme Sensitivity in IR Region

We theoretically propose a surface plasmon resonance (SPR)-based fiber optic refractive index (RI) sensor. A surface plasmon exciting metallic grating formed with the alternation of indium tin oxide (ITO) and silver (Ag) stripes is considered on the core of the fiber. A thin film of silicon is used as an overlay. Silicon film not only protects the metallic grating from oxidation but also enhances the field to improve the device sensitivity. The sensor is characterized in terms of sensitivity, detection accuracy (DA), figure of merit (FoM), and quality factor (QF). The maximum sensitivity in the RI range 1.33 to 1.38 refractive index unit (RIU) is reported to be?~25 µm/RIU in infra-red region of investigation.

     

Parallel-scan based microarray imager capable of simultaneous surface plasmon resonance and hyperspectral fluorescence imaging

With the development of the microarray technology, demands for array detection techniques become higher and higher. For many microarrays, several biomolecular interactions occur simultaneously and the interplay of various factors that affect these interactions remains poorly understood. Detecting such interactions with a single technique can often be a difficult and complicated process. In this work we propose a combined technique which enables simultaneous angle-interrogation surface plasmon resonance (SPR) sensing and hyperspectral fluorescence imaging. This tandem technique offers two-dimensional imaging of the whole array plane. The refractive index information obtained from SPR sensing and the physicochemical properties obtained from fluorescence imaging provide a comprehensive analysis of biological events on the array-chip. In addition, SPR and fluorescence detection techniques confirm each other in experimental results to exclude false-positive or false-negative cases. In terms of SPR sensing performance, the refractive index resolution is 3.86 × 10⁻⁶ refractive index units (RIU), and the detection limit is 10⁴ cfu/ml of Escherichia coli bacteria. The resolving power and detection sensitivity of fluorescence imaging are approximately 20 μm and 0.61 fluors/μm², respectively. Finally, two model experiments, detecting the DNA hybridization and biotin–avidin interactions respectively, demonstrate the biomedical application of this system.     

Analysis of a Surface Plasmon Resonance Probe Based on Photonic Crystal Fibers for Low Refractive Index Detection

A photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) probe with gold nanowires as the plasmonic material is proposed in this work. The coupling characteristics and sensing properties of the probe are numerically investigated by the finite element method. The probe is designed to detect low refractive indices between 1.27 and 1.36. The maximum spectral sensitivity and amplitude sensitivity are 6 × 10³ nm/RIU and 600 RIU^?1, respectively, corresponding to a resolution of 2.8 × 10^?5 RIU for the overall refractive index range. Our analysis shows that the PCF-SPR probe can be used for lower refractive index detection.     

Alphabetic-Core Assisted Microstructure Fiber Based Plasmonic Biosensor

Light control capability of photonic crystal fiber (PCF) is a unique feature which can be applied to improve biosensing and plasmonic performance. Here, we reported alphabetic-core microstructure fiber-based plasmonic biosensor. Three different alphabetic R-, M-, and S-shaped cores of PCF-based plasmonic microstructures show controllable light propagation to enhance biosensor sensitivity and resolution. The light-guiding properties and sensing performance are investigated numerically using the finite element method (FEM). The proposed R-shaped core (RSC), M-shaped core (MSC), and S-shaped core (SSC) PCF-based plasmonic sensors show the maximum wavelength and amplitude sensitivities of 12,000, 11,000, 10,000 nm/RIU and 478, 533, and 933 RIU⁻¹, respectively, in the refractive index (RI) range of 1.33 to 1.40. The sensors also exhibit promising wavelength resolution of 8.33 × 10⁻⁶, 9.09 × 10⁻⁶, and 1.0 × 10⁻⁶ RIU, with figure of merit (FOM) of 108, 143, and 217 RIU⁻¹ for RSC, MSC, and SSC PCFs, respectively. The tunable sensing performance is also observed in design structures due to controllable light traveling path and their interaction with analytes. The proposed alphabetic-core PCF SPR sensors would be a promising candidate for the application of light controlling, trapping in microscale environment, and biosensing.

     

Platinum Layers Sandwiched Between Black Phosphorous and Graphene for Enhanced SPR Sensor Performance

Highly sensitive surface plasmon resonance (SPR) sensor consisting of Ag-Pt bimetallic films sandwiched with 2D materials black phosphorus (BP) and graphene over Pt layer in Kretschmann configuration is analyzed theoretically using the transfer matrix method. Numerical results show that upon suitable optimization of thickness of Ag-Pt layers and the number of layers of BP and graphene, sensitivity as high as 412°/RIU (degree/refractive index unit) can be achieved for p-polarized light of wavelength 633 nm. This performance can be tuned and controlled by changing the number of layers of BP and graphene. Furthermore, the addition of graphene and heterostructures of black phosphorus not only improved the sensitivity of the sensor but also kept the FWHM of the resonance curve much smaller than the conventional sensor utilizing Au as plasmonic metal and hence improved the resolution to a significant extent. We expect that this new proposed design will be useful for medical diagnosis, biomolecular detection, and chemical examination.

     

Self-Referencing Plasmonic Array Sensors

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.

     

Development of a benzene vapour sensor utilizing chemiluminescence on Y2O3

Chemiluminescence (CL) was observed when benzene vapour passed through the surface of Y₂O₃, TiO₂, Y₂O₃–V₂O₅, TiO₂–Y₂O₃, Y₂O₃–Cr₂O₃, Y₂O₃–Al₂O₃ and TiO₂–Al₂O₃, with air as the carrier gas. The strongest CL intensity was found with Y₂O₃ as the catalyst. A novel benzene sensor based on this kind of CL was developed. Quantitative analysis was performed at the wavelength of 425 nm. Under optimal conditions, CL intensity was directly proportional to the concentration of benzene vapour. The linear range was 4–7018 mg/m³ (r = 0.9981, n = 11), with a detection limit of 1 mg/m³ (the signal:noise ratio was 3). This gas sensor can work continuously for >80 h and has been successfully applied to the real‐time determination of benzene vapour. Copyright © 2008 John Wiley & Sons, Ltd.     

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

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.     

Long-Range Surface Plasmon Resonance–Based Sensitivity Study on D-shaped Ag-MgF2-Coated Models with Analyte Variations

In this report, a novel D-shaped long-range surface plasmon resonance (LRSPR) fiber base sensor has been introduced. The demonstration of proposed sensor involves two D-shaped silver-coated models to study the sensitivity responses. The entire study with the constructed models is based on a single-mode fiber. The models are multilayered consisting of metal, dielectric, and analyte as separate layers. Silver (Ag) and magnesium fluoride (MgF2) strips are used as metal and dielectric layers respectively. The constituency of analyte as an interface excellently standardized the models for sensitivity detection. In this report, a large range of analyte refractive indices (RI) which varies from 1.33 to 1.38 is appraised for the proposed models to characterize the sensitivity. The entire context is encompassed by the wavelength region from 450 to 850 nm with an interval of 20 nm. Sensitivities in this report are measured based on the analyte position from the core and metal for both models. For each of the two models, the analyte is placed as the top layer. RIs of the applied metal (Ag) are measured using the Drude-Lorentz formula. The simulated sensitivities for model-1 and model-2 vary from 6.3?×?10³ nm/RIU to 8.7?×?10³ nm/RIU.

     

Dual-wavelength plasmonic perfect absorber suitable for refractive index sensing

In this paper, a plasmonic perfect absorber (PPA) based on metal-insulator-metal-insulator-metal (MIMIM) structure has been designed for refractive index sensing of glucose solutions (analyte) and then a new method has been proposed for fast, low-cost, and easy measurement of sensor’s sensitivity. Simulation results show that the absorption spectrum of the proposed sensor has two resonance peaks that with an increase in analyte refractive index, both of them are red-shifted. In our proposed measurement technique, two conventional single-wavelength lasers (with wavelengths of 1050 nm and 1750 nm) are used for vertical plane wave light illumination on the structure. Then, the absorbed powers at 1750 nm (A₂) and 1050 nm (A₁) wavelengths are calculated and variation of the absorption ratio (A₂/A₁) due to change of analyte refractive index would be introduced as the sensitivity of sensor (S = Δ(A₂/A₁)/Δn). Obtained results show that the increase of analyte refractive index from n = 1.312 to n = 1.384 will result in an increase of sensor’s sensitivity from 9.3/RIU to 33.475/RIU.