Analyte Refractive Index Research Articles

Highly sensitive photonic crystal fiber sensor based on surface plasmon resonance for low refractive index detection

A photonic crystal fiber (PCF) sensor based on surface plasmon resonance with a gold film coating is designed and investigated for detecting the analytes with a low refractive index (RI). The critical geometry parameter is optimized by the finite element method to increase the sensitivity of the sensor. An open-ring structure with a 70-nm-thickness gold film coated on the inner surface is located on the left and right sides of the PCF sensor, and its angle is equal to or greater than 90 deg. The spectral and amplitude sensitivities are numerically calculated to evaluate the sensing performance of the proposed sensor. The simulation results indicate that the maximum and average sensitivities are 68,000 and 9583 nm / RIU, respectively. The resolution is a critical parameter for assessing the sensing performance of the sensor with a maximum value of 1.47 × 10 − 6 RIU. The simulation results show that the RI of analytes that the sensor can detect ranges from 1.20 to 1.31. Therefore, the sensor possesses wide application prospects in the field of biosensors.

Plasmonic micro-channel based highly sensitive biosensor in visible to mid-IR

A strong light coupling between core-guided mode and metal layer leads to the enhancement of plasmonic sensor performance significantly. In this work, a plasmonic metal coated micro-channel based surface plasmon resonance sensor is proposed where a micro-channel is introduced to increase the mode coupling by reducing the distance between the core and analyte channel. Gold (Au) is considered to coat the micro-channel and generate surface plasmon on the fiber surface. Titanium dioxide (TiO2) is employed to stick the Au layer tightly with the silica which assists in shifting the sensing wavelength from visible to mid-IR region. The light-guiding and bio-sensing properties of the proposed D-shaped sensor performance is numerically investigated by employing the finite element method. The sensor obtained maximal wavelength and amplitude sensitivities of 1,21,000 nm/Refractive index unit (RIU) and 1,405 RIU−1, respectively in the x-polarized mode. Moreover, the sensor exhibits an extremely high resolution of 8.26 × 10−7 RIU and the limit of detection (LOD) is 6.83 × 10−12 RIU2/nm, respectively, in the wavelength interrogation technique. To the best of our knowledge, the proposed sensor shows the highest wavelength sensitivity, resolution and LOD when compared to the existing PCF based SPR sensors. Due to the extremely sensitive response, the proposed sensor will enhance the unknown analyte detection capability significantly. Furthermore, the broad sensing range of analyte refractive index (RI) variation from 1.33 to 1.44 makes the sensor suitable for biochemical as well as medical diagnostic applications.

The role of Ta2O5 thin film on a plasmonic refractive index sensor based on photonic crystal fiber

In this paper, a highly sensitive plasmonic refractive index (RI) sensor based on photonic crystal fiber (PCF) is proposed. Silver (Ag) is used as plasmonic material and tantalum pentoxide (Ta2O5), high RI material, is used as an overlayer over the silver thin film. The sensor performance is realized using surface plasmon resonance (SPR) phenomenon. The effect of tantalum pentoxide overlayer thickness on sensing parameter as well as on sensitivity is analyzed in detail using finite element method (FEM). The detailed study shows an interesting property that the increasing Ta2O5 layer thickness can tune the operating analyte RI from high RI region to low RI region i.e. towards the aqueous medium. The structural parameters of the proposed sensor are being optimized and its sensitivity is realized using wavelength interrogation technique. A maximum sensitivity of 50000 nm/RIU is reported. This study, no doubt, provides a new direction of designing RI sensor that could tune RI range by varying the only the Ta2O5 layer thickness to the desired operating analyte region. Besides, the simple design feasibility, low fabrication cost and portable nature of the proposed sensor make it suitable for industrial and chemical sensing applications.

Highly Sensitive D-Shaped Plasmonic Refractive Index Sensor for a Broad Range of Refractive Index Detection

In this paper, an extremely sensitive Photonic Crystal Fiber (PCF) based Surface Plasmon Resonance (SPR) sensor having D-shaped structure has been proposed. Gold has been used as the plasmonic material, and it has been coated outside of the fiber on its glassy surface to detect the change in the refractive index of the surrounding medium. Gold has been chosen as it is chemically stable and has no impact on the surrounding aqueous medium. Maximum Wavelength Sensitivity (WS) of 216,000 nm/RIU and Amplitude Sensitivity (AS) of 1680 RIU−1 have been achieved for the analyte refractive index range 1.23 to 1.42 by the proposed sensor. After conducting a detailed literature review in the relevant field, it has been revealed that the proposed sensor possesses the highest wavelength sensitivity among recently reported PCF-SPR sensors to this date. The proposed sensor also exhibits a resolution of 4.63 × 10−7 RIU and FOM of 1200. Consequently, the proposed sensor can become an ideal candidate in the field of biomedical sensing, chemical sensing, and other lower RI analytes sensing.

A theoretical design of evanescent wave biosensors based on gate-controlled graphene surface plasmon resonance

A surface plasmon resonance (SPR) sensor based on gate-controlled periodic graphene ribbons array is reported. Different from the conventional methods by monitoring reflectivity variations with respect to incident angle or wavelength, this approach measures the change in SPR curve against the variation of graphene chemical potential (via dynamically tuning the gate voltage) at both fixed incident angle and wavelength without the need of rotating mirror, tunable filter or spectrometer for angular or wavelength interrogation. Theoretical calculations show that the sensitivities are 36,401.1 mV/RIU, 40,676.5 mV/RIU, 40,918.2 mV/RIU, and 41,160 mV/RIU for analyte refractive index (RI) equal to 1.33, 1.34, 1.35 and 1.36; their figure of merit (1/RIU) are 21.84, 24, 23.74 and 23.69, respectively. Significantly, the enhancement in the non-uniform local field due to the subwavelength graphene ribbon resonator can facilitate the detection in redistribution of protein monolayers modeled as dielectric bricks.

Surface plasmon resonance based highly sensitive gold coated PCF biosensor

A highly sensitive surface plasmon resonance-based PCF biosensor is explored in this research work. Outside the fiber frame, active plasmonic material gold (Au) with a thickness of 25 nm has been deposited which is chemically steady and is the primary sensing layer of the presented sensor. Unknown analytes could be detected by being flown on the metal surface or leaked onto the metal layer’s outer surface. In this paper, we used circular airholes for external sensing of the unknown analyte. The suggested sensor obtains the maximum wavelength sensitivity of 14,500 nm / RIU in X-polarization mode and the maximum amplitude sensitivity of 4738.9 $${\mathrm{RIU}}^{-1}$$ for Y-polarized mode, respectively in the spectrum of 1.35–1.41 for the analyte refractive index (RI). The lowest wavelength sensor resolution offered by this sensor is 6.9× $${10}^{-6}$$ RIU and the lowest amplitude sensor resolution is 2.11×10-6 RIU for Y-polarized mode with FOM of 387 and 364 for X and Y polarization. In the presence of a perfectly matched layer (PML), the sensing output of the presented sensor is analyzed using the finite element method (FEM) based software named COMSOL Multiphysics version 5.3a. From our simulation result, it is important to note that the proposed sensor demonstrates a noteworthy sensor performance for both polarization modes so that the choice of light sources during the practical implementation is more frequent. The findings also show some bright features that our proposed sensor can detect organic chemicals, biochemical analytes and can also be used in medical diagnostics immensely.

Plasmonic Biosensor for Low-Index Liquid Analyte Detection Using Graphene-Assisted Photonic Crystal Fiber

We report a sensitive D-shaped photonic crystal fiber-based surface plasmon resonance (PCF-SPR) sensor with linear sensing performance and a broad detection range for low refractive index (RI) liquid analytes ranging from 1.27 to 1.37 with possible extension beyond this range. We examine three combinations of materials (silver only, graphite on silver, and graphene on silver) as plasmonic nanofilm for the PCF-SPR and demonstrate that graphene-assisted PCF has the best overall performance. We show that graphene coating of silver nanofilm improves the sensitivity and the overall figure of merit of the sensor, besides the practical benefit of protecting the silver nanofilm from surface oxidation. Furthermore, we propose two distinct ways of analyte sensing based on filling patterns where the liquid analyte can be filled internally into the top two air holes of the PCF, or externally into a rectangle channel at the top of the fiber. In the internal filling detection scheme, the graphene-assisted PCF-SPR sensor demonstrates ultra-linearity, a detection range of 0.1 refractive index unit (RIU) between 1.27 and 1.37, an average linear spectral sensitivity of 2320 nm/RIU, and a maximum amplitude sensitivity of 192 RIU−1 for 1150 nm excitation. In the external filling detection scheme, the PCF-SPR exhibits extremely large sensitivities with a maximum spectral sensitivity of 22,400 nm/RIU close to analyte RI of 1.33, and a maximum figure of merit (FOM) of 127 which is approximately five times larger than that of the similar reported PCF-SPR sensors in the literature. The combination of a broad detection range for low-index analytes, large sensitivities, design flexibility, and stability against surface oxidation renders our proposed sensor as an interesting candidate for biosensing applications in chemistry, biology, and medicine.

Design and Analysis of a Biochemical Sensor Based on Surface Plasmon Resonance with Ultra-high Sensitivity

We present a simple, unique, and highly sensitive surface plasmon resonance (SPR)-based photonic crystal fiber (PCF) biosensor. Besides having very high sensitivity, our proposed sensor is also fabrication friendly. The finite element method (FEM) of COMSOL 5.3a was utilized to devise the sensor’s structure and analyze the impact of changing geometric parameters on this biosensor’s overall performance. Gold (Au) or AZO (aluminum-doped zinc oxide) can be utilized to create excitation between the two modes (core and plasmonic). We have tried to vary different parameters of the PCF, and we observed in simulation results a very high amplitude sensitivity (AS) of 4358.09 RIU−1, maximum wavelength sensitivity (WS) of 21,000 nm/RIU (refractive index unit), a high figure of merits (FOM) of 729 with a sensor resolution of 4.76 × 10−6 RIU and 2.29 × 10−6 RIU for wavelength, and amplitude respectively when gold was utilized as the plasmonic material. Replacing gold by AZO resulted in the corresponding values of 3908 RIU−1, 1700 nm/RIU, 792, 5.88 × 10−5 RIU, and 2.56 × 10−6 RIU. Analyte refractive index (RI) ranges between 1.33–1.42 for gold and 1.31–1.39 for AZO. We believe the high performance of our proposed SPR based PCF biosensor in terms of sensitivity will bring a promising advancement in the field of unknown analyte detection and biological organic chemicals.

Analysis of Double Peak Detection in a D-Shaped Photonic Crystal Fiber Plasmonic Sensor

We present a novel D-shaped photonic crystal fiber sensor with double loss peaks based on surface plasmon resonance. The proposed sensor has a lot of better characteristics for refractive index detection compared with single-peak sensor. It is worth noting that the trough of the loss spectrum keeps unchanged as the analyte refractive index increases, which indicates that this sensor is extremely stable. In addition, numerical simulation shows that the average wavelength sensitivity can reach 29,000 nm/RIU and the maximum resolution is as high as 3.45 × 10−5 RIU. Furthermore, the coupling theory between fundamental mode and the surface plasmon polarization (SPP) mode is investigated in this paper. It is found that there is obvious competition between the resonant modes. This study has enlightening significance for us to understand the generation mechanism of polarization-entangled quantum photo source.

Photonic Crystal Fiber Based Biosensor for Pseudomonas Bacteria Detection: A Simulation Study

The detection of microorganisms like Pseudomonas are very important as they trigger an infection in human blood, lungs, and different parts of the body causing various ailments. In this paper, a surface plasmon resonance (SPR) biosensor based on photonic crystal fiber (PCF) has been proposed to detect the presence of Pseudomonas bacteria with attractive performance characteristics. The sensor is designed using a simple circular lattice of PCF, coated with a thin chemically stable gold layer. The performance investigation of the sensor is numerically carried out by using a finite element (FE) based simulation tool where the highest wavelength and amplitude sensitivity are found as 20,000 nm/RIU and 1380 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , respectively. The sensor shows an excellent spectral resolution of the highest value of 5.26×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> RIU, ensuring the capability of identifying a very small change in analyte refractive index (RI) within the range of 1.33 to 1.42. The performance investigation is also carried out altering the diameter of air holes, pitch, and gold layer thickness to explore the variation in phase matching conditions due to the change in structural parameters. As the sensor is adept at detecting the sample with high sensitivity and sensing resolution, the proposed sensor can be highly efficient in detecting Pseudomonas bacteria as well as other organic compounds, and biological analytes.

Quasi-D-Shaped Fiber Optic Plasmonic Biosensor for High-Index Analyte Detection

In this paper, we propose a highly sensitive quasi-D-shaped fiber optic biosensor for detection of high refractive index (RI) liquid analytes via surface plasmon resonance. The main mechanism of sensing is interplay between photonic crystal fiber fundamental mode and plasmonic mode which leads to formation of different resonance peaks depending on the analyte RI. We numerically analyze the structure sensitivity to design parameters and demonstrate the sensing performance of the proposed biosensor using both spectral sensitivity and amplitude sensitivity methods. The proposed biosensor has a RI detection range of 0.15 refractive index unit (RIU) from 1.45 to 1.6. The sensor exhibits linear sensing performance with a RI spectral sensitivity of 9300 nm/RIU for analyte RI ranging from 1.45 to 1.525, 1176 nm/RIU for analyte RI ranging from 1.525 to 1.6 and in particular, 11800 nm/RIU for analyte RI between 1.475 and 1.5. Furthermore, an average RI sensitivity of 4800 nm/RIU for analyte RI ranging from 1.45 to 1.6 is demonstrated. We also study the amplitude sensitivities of the proposed sensor which show promising maximum values of 183.6 RIU $^{-1}$ for 785 nm excitation and 820 RIU $^{-1}$ for 1050 nm excitation. Due to the simple structure of the proposed biosensor, large detection range, high sensitivity and promising linear sensing performance, the proposed biosensor can be a promising candidate for detecting various high RI chemical and biochemical samples.

Microsphere Photolithography Patterned Nanohole Array on an Optical Fiber

Microsphere Photolithography (MPL) is a nanopatterning technique that utilizes a self-assembled monolayer of microspheres as an optical element to focus incident radiation inside a layer of photoresist. The microspheres produces a sub-diffraction limited photonic-jet on the opposite side of each microsphere from the illumination. When combined with pattern transfer techniques such as etching/lift-off, MPL provides a versatile, low-cost fabrication method for producing hexagonal close-packed metasurfaces. This article investigates the MPL process for creating refractive index (RI) sensors on the cleaved tips of optical fiber. The resonant wavelength of metal elements on the surface is dependent on the local dielectric environment and allows the refractive index of an analyte to be resolved spectrally. A numerical study of hole arrays defined in metal films shows that the waveguide mode provides good sensitivity to the analyte refractive index. This can be readily tuned by adjusting the MPL exposure and the simulation results guide the fabrication of a defect tolerant refractive index sensor on the tip of a fiber tip with a sensitivity of 613 nm/RIU. The conformal nature of the microsphere monolayer simplifies the fabrication process and provides a viable alternative to direct-write techniques such as Focused Ion Beam (FIB) milling.

Surface plasmon based fiber optic refractive index sensor

This paper has proposed a surface plasmon resonance-based photonic crystal fiber (PCF) sensor to detect even a small change in refractive index (RI) values of analytes. The impact on sensor performance by Bezier polygon core structure of the PCF and gold coating in an air hole have been carried out. The sensor resonance wavelength and the respective confinement loss are analyzed for various Bezier polygon parameters and for various gold coating thicknesses. Also, a comparison between gold filling and gold coating in an air hole of PCF have been undertaken to show the superiority of the gold coating in sensor performance. The promising sensor performance has been noted down above the analyte RI of about 1.3 with an upright sensitivity of about 7000 nm/RIU. This type of sensor is of great interest in medical and industrial applications.

Ultra-sensitive hexagonal PCF-SPR sensor with a broad detection range

ABSTRACT A photonic crystal fibre (PCF) sensor based on surface plasmon resonance (SPR) with a hexagonal structure and external gold coating is designed and demonstrated to have a broad detection range and ultra-high sensitivity. Gold is chosen as the plasmonic materials due to the inert and stable chemical properties and the gold coating on the PCF-SPR sensor also simplifies the detection and fabrication processes. The sensing properties are analysed by the finite element method (FEM). In this sensor, the y-polarized mode with the large mode field area shows better performance such as the high spectral sensitivity of 28,700 nm/RIU, wide analyte refractive index (RI) range from 1.28 to 1.43, resolution of 3.48×10-6 RIU, and maximum amplitude sensitivity of 2481.06 RIU−1. Furthermore, the paragon figure of merit and signal-to-noise ratio of the sensor are 517.81 RIU−1 and 5.18, respectively.

Study of highly sensitivity metal wires assisted photonic crystal fiber based refractive index sensor

In this paper, a photonic crystal fiber (PCF) sensor based on surface plasmon resonance is proposed for refractive index (RI) sensing with improved sensitivity and resolution. In this design, solid core PCF with three layers of holes is used. Instead of a coating metal layer, we have used two metal wires at both sides of the outside layer of fiber to originate surface plasmon resonance for detection of RI of analyte effectively. Design and analyses have been performed by a Full vectorial finite element method (FV-FEM). Metals Cu, Au, and Ag have been used as plasmonic materials that exhibit higher wavelength sensitivity 7300 nm/RIU, 6200 nm/RIU, and 6100 nm/RIU, respectively. For Cu metal, we observe maximum amplitude sensitivity 597 RIU−1 with higher resolution 1.36 × 10–5 RIU for refractive index of range 1.31–1.36. However, the average sensitivity for Cu, Au, and Ag are 4320 nm/RIU, 4275 nm/RIU, and 3950 nm/RIU, respectively. The effect of air holes along with metal wires for sensitivity is also investigated. In results, copper has provided better sensitivity as well as resolution for a long-range analyte for this proposed RI sensor.

Highly sensitive near-infrared surface plasmon resonance (SPR) sensor based on birefringent six-core photonic crystal fibre

A new type of highly sensitive near-infrared birefringent six-core photonic crystal fibre sensor using surface plasmon resonance (SPR) is proposed. By using the full-vector finite element method, the impacts of the fibre parameters on the wavelength sensitivity and amplitude sensitivity are numerically studied. The numerical results indicate that, benefiting from the high birefringent multi-core fibre structure, an average sensitivity of 8083 nm/refractive index unit (RIU) within the wavelength range from 1.532 to 2.02 µm is achieved when the analyte refractive index (RI) lies in (1.372, 1.432). Moreover, the maximum amplitude sensitivity is as high as 226 RIU−1 if the analyte RI is adjusted from 1.372 to 1.382. In consideration of its excellent sensing performance, the proposed SPR multi-core PCF sensor can be applied in environmental, food safety, and (bio)chemical detection.

Plasmonic sensor utilizing Ti3C2Tx MXene layer and fluoride glass substrate for bio- and gas-sensing applications: Performance evaluation

The two-dimensional (2D) heterostructure of black phosphorus (BP)–MXene shows great stability in liquid and gaseous environments. Sensitivity enhancement of a surface plasmon resonance (SPR) sensor utilizing BP and Ti3C2Tx MXene layer is proposed in this work. A CaF2 glass prism is considered as the coupling substrate and 2D Ti3C2Tx MXene as analyte interacting layer. The sensor’s performance is demonstrated in terms of sensitivity and figure-of-merit (FOM) values at an operating wavelength of 633 nm. An extremely high angular sensitivity of 322.46°/RIU is obtained, with a significant FOM value of 55.596/RIU (analyte refractive index ∼ 1.33) for three-layer BP–Ti3C2Tx MXene monolayer based SPR sensor. Further, the sensing of gaseous analyte using the proposed sensor structure is also explored. This work will open new avenues for application of BP–MXene heterostructure in various optoelectronic devices.

A hollow dual-core PCF-SPR sensor with gold layers on the inner and outer surfaces of the thin cladding

A hollow dual-core photonic crystal fiber (PCF) with high sensitivity based on surface plasmon resonance (SPR) sensing is designed and analyzed numerically by the finite element method (FEM). This double-sided gold structure has not been reported before and provides a novel mechanism of SPR excitation. In order to increase coupling effects between the plasmonic mode and the fundamental mode, double-sided gold films deposited on both inner and outer surface are selected. The sensing properties are enhanced remarkably by depositing gold films on the inner and outer surfaces of the thin cladding as manifested by more than 50 times improvement in the average sensitivity compared to the single-sided gold structure. The working wavelength of the sensor is controllable in the near-infrared region (1550–2700 nm) for analyte refractive indices (RIs) ranging from 1.36 to 1.41. Numercal simulation reveals that the average and maximum spectral sensitivities rise to 23,000 nm/RIU and 30,000 nm/RIU and the corresponding resolution is improved to 3.33 × 10−6 RIU. Compared with the unilaterally coated sensor with the same structural parameters, this bilaterally coated sensor offers distinctive advantages that are beneficial to the development of photonic sensors with ultrahigh sensitivity.

Performance analysis of optical fiber surface plasmon resonance sensor in single-mode operation region

Abstract A new approach for studying the performance of single-mode optical fiber surface plasmon resonance sensor for refractive index sensing is presented. Intensity interrogation technique is used to observe and examine the effect of changing the value of the operating wavelength, within the single-mode operation region, on sensor performance. Effect of changing metal thickness, which is a critical parameter of the sensor structure, is also investigated. The results show that the selected operating wavelength within the mentioned region plays a very important role and has a significant impact on the sensor sensitivity. As the operating wavelength increases beyond the cut-off wavelength, above which the first higher-order mode disappears, the sensitivity increases while the refractive index range, for which the sensitivity is above its half maximum value, becomes narrower. In the proposed sensor structure, for a metal thickness of 25 nm, the maximum sensitivity reaches 2554 RIU−1 for analyte refractive index of 1.439 at a wavelength of 1500 nm. This sensitivity corresponds to a resolution of order 106 RIU by assuming 1% minimum reflectivity variation. The operating wavelength should be carefully selected and changed according to the refractive index values intended to be measured to ensure high sensor sensitivity at these values. The analysis provided in this paper enables to select and change the desired range of the sensed refractive index using low cost technique by just changing the operating wavelength in the single-mode operation region.

Cascaded wavelength multiplexed refractive index sensors in optical fibers based on surface plasmon resonances

Surface plasmon resonance (SPR) based cascaded wavelength multiplexed fiber-optic sensors provide immense scope for multi-channel and multi-analyte detection benefiting from all the advantages prerogative to single-channel fiber-optic sensors. This work describes the numerical simulations carried out for performance analysis of SPR based refractive index (RI) sensor implemented in cascaded dual- and triple-channel fiber-optic configurations using thin films of Ag, Cu, and Au as plasmonic metals and ZnO and Si as high RI overlayers. A dual-channel sensor is simulated using Ag and Cu/ZnO layers in two well-separated sensing channels on a multimode optical fiber, while a triple-channel sensor is studied using Ag, Cu/ZnO, and Au/Si in the three sensing channels. Due to different SPR resonance wavelengths of Ag, Cu, and Au, distinct sets of SPR spectra are obtained when the sensor response is analyzed by varying analyte RIs circumscribing different sensing regions of the cascaded fiber-optic probe. This feature furnishes an efficient option for easy tailoring of operating range of the sensor desired for different applications. The reported results provide promising perspectives for in-line sensing applications to analyze different constituents of the mixtures of biomolecules, clinical samples, petroleum products, and others.