Grapefruit fiber filled with silver nanowires surface plasmon resonance sensor in aqueous environments

Machine learning-enhanced surface plasmon resonance based photonic crystal fiber sensor

This study introduces what we believe to be a novel photonic crystal fiber sensor utilizing surface plasmon resonance (SPR), incorporating four gold nanowires to enhance sensing capabilities. The research employs machine learning, specifically artificial neural networks (ANN), to predict confinement loss and sensitivity, achieving high accuracy without needing the imaginary part of the effective refractive index. The machine learning technique is applied in three different scenarios, resulting in mean squared errors of 0.084, 0.002, and 0.003, highlighting the reliability of the ANN models in predicting sensor outputs. Additionally, the sensor demonstrates impressive wavelength sensitivities of 2000-18000 nm/RIU (nanometers per refractive index unit) for refractive indices of 1.31-1.4 within the 720-1280 nm wavelength range, and a notable maximum amplitude sensitivity of 889.89 RIU-1. This integration of SPR, photonic crystal fiber, and machine learning not only optimizes sensor performance but also offers an efficient methodology for prediction, showcasing the potential of machine learning in advancing optical sensor design.

Numerical analysis of Phase change material and graphene-based tunable refractive index sensor for infrared frequency spectrum

Here, we present the findings of parametric analysis into a phase transition material Ge2Sb2Te5(GST)-based, graphene-based, with a wide dynamic range in the infrared and visible electromagnetic spectrum. The suggested structure is studied in multi-layered configurations, built up with layers of GST, graphene, silicon, and silver materials. These multilayer structures' reflectance behavior has been described for refractive indices between 1.3 and 2.5. The complete design is simulated using a computational process called the finite element method. Additionally, we have investigated the impact of material heights on the structure's performance in general. We have presented several resonating tracing curves in polynomial equations to determine the sensing behavior across a specific wavelength range and refractive index values. The proposed design is also investigated at various inclined angles of incidence to ascertain its wide-angle stability. A computational study of the proposed structure can assist in the evolution of biosensors to identify a wide range of biomolecules, including malignant, hemoglobin urine, saliva-cortisol, and glucose.

Asymmetric core-guided polarization-dependent plasmonic biosensor

A modified solid-core photonic crystal fiber (PCF)-based plasmonic sensor is proposed where light propagation through the PCF is controlled by scaling down of air holes. The modified core facilitates the easy excitation of the plasmonic surface, resulting in improved sensor performance. The chemically stable gold is externally coated on the PCF surface, which helps to establish surface plasmon resonance phenomena. The response of the sensor is analyzed based on the numerical method, and the design parameters are optimized to enhance the sensing performance. The asymmetric fiber-core structure provides the polarization controllability and significantly suppresses the y-polarized response to achieve a dominant x-polarized response and additional functionalities. The sensor exhibits a maximum wavelength sensitivity of 11,000 nm/RIU (refractive index unit) and sensing resolution of 9.09×10^-6 RIU in the x-polarized mode. Also, the sensor exhibits maximum amplitude sensitivity of 631RIU^-1, and a good figure of merit is 157RIU^-1. Furthermore, the sensor can detect the unknown analytes' refractive index (RI) in the sensing analyte RI range of 1.33 to 1.40, which will lead to finding the potential applications in biomolecules, organic chemicals, and environment monitoring.

Sensitivity Enhancement of a Concave Shaped Optical Fiber Refractive Index Sensor Covered with Multiple Au Nanowires

In the present paper, a new kind of concave shaped refractive index sensor (CSRIS) exploiting localized surface plasmon resonance (LSPR) is proposed and numerically optimized. The LSPR effect between polaritons and the core guided mode of designed CSRIS is used to enhance the sensing performance. The sensor is characterized for two types of sensing structures coated with gold (Au) film and Au nanowires (AuNWs), respectively. The influence of structural parameters such as the distance (D) of the concave shaped channel (CSC) from the core, the diameter of the nanowire (d_n) and the size (s) of the CSC are investigated here. In comparison to Au film, the AuNWs are shown to significantly enhance the sensitivity and the performance of the designed sensor. An enhanced sensitivity of 4471 nm/RIU (refractive index unit) is obtained with AuNWs, for a wide range of analytes refractive index (n_a) varying between 1.33 to 1.38. However, for conventional Au film; the sensitivity of 808.57 nm/RIU is obtained for the same range of analytes.

Recent Advances in Plasmonic Sensor-Based Fiber Optic Probes for Biological Applications

The survey focuses on the most significant contributions in the field of fiber optic plasmonic sensors (FOPS) in recent years. FOPSs are plasmonic sensor-based fiber optic probes that use an optical field to measure the biological agents. Owing to their high sensitivity, high resolution, and low cost, FOPS turn out to be potential alternatives to conventional biological fiber optic sensors. FOPS use optical transduction mechanisms to enhance sensitivity and resolution. The optical transduction mechanisms of FOPS with different geometrical structures and the photonic properties of the geometries are discussed in detail. The studies of optical properties with a combination of suitable materials for testing the biosamples allow for diagnosing diseases in the medical field.

Plasmonic Interface Modified with Graphene Oxide Sheets Overlayer for Sensitivity Enhancement

A novel strategy to modify the plasmonic interface by spin-coating an overlayer of graphene oxide sheets (GOSs) on top of the surface plasmon resonance (SPR) sensor is proposed and demonstrated. Thanks to the excellent electrical conductivity, large surface area, and high-refractive index of the GOSs layer, the GOSs-modified SPR (GOSs-SPR) sensor achieves an improved sensitivity in the detection of bulky refractive index solutions and bovine serum albumin (BSA) solutions. The maximum sensitivity of 2715.1 nm/RIU achieved by three spin-coatings shows an enhancement of 20.2% than the case without the modification of the GOSs overlayer. Benefiting from the large surface area and abundant surface functional groups, the GOSs-SPR sensor has a greater sensitivity enhancement (up to 39.35%) in the detection of the BSA molecules. Most importantly, we have firstly experimentally demonstrated that the GOSs overlayer with thickness over hundreds nanometers can still lead to a great enhancement of sensitivity of SPR sensors. Additionally, the proposed modification method for the plasmonic interface is a simple and effective strategy to boost the sensitivity in a chemical-free and environment-friendly manner, without additional chemical or biological amplification steps. These unique features make the proposed GOSs-SPR biosensor a low-cost and biocompatible platform in the fields of biochemical sensing, drug screening, and environmental monitoring.

Analysis of High Sensitivity Photonic Crystal Fiber Sensor Based on Surface Plasmon Resonance of Refractive Indexes of Liquids

A photonic crystal fiber (PCF) sensor based on gold nanowires able to detect changes in surface plasmon resonance (SPR) was proposed and numerically investigated through the finite element method. To facilitate real-time detection, the analyte in this sensor was located outside the optical fiber. The effects of diameters of both air hole and gold wires on the sensing characteristics of the sensor were discussed. The sensor was designed to detect liquids with refractive indexes ranging between 1.33 and 1.36. The numerical simulations indicated that sensor structure improved its functionality. The maximum spectral sensitivity reached 9200 nm/RIU over the entire refractive index range. The average spectral sensitivity was estimated to be 5933 nm/RIU, and corresponded to a sensor resolution of 2.81 × 10⁻⁶ RIU. These findings look very promising for future use in detection of liquid.

Ultrahigh sensitivity refractive index sensor of a D-shaped PCF based on surface plasmon resonance

We propose a D-shaped photonic crystal fiber (PCF) refractive index sensor with ultrahigh sensitivity and a wide detection range. The gold layer is deposited on the polished surface, avoiding filling or coating inside the air holes of the PCF. The influences of the gold layer thickness and the diameter of the larger air holes are investigated. The sensing characteristics of the proposed sensor are analyzed by the finite element method. The maximum sensitivity can reach 31,000  nm/RIU, and the refractive index detection range is from 1.32 to 1.40. Our proposed PCF has excellent sensing characteristics and is competitive in sensing devices.

Analysis of Hollow Fiber Temperature Sensor Filled with Graphene-Ag Composite Nanowire and Liquid

A hollow fiber temperature sensor filled with graphene-Ag composite nanowire and liquid is presented and numerically characterized. The coupling properties and sensing performances are analyzed by finite element method (FEM) using both wavelength and amplitude interrogations. Due to the asymmetrical surface plasmon resonance sensing (SPR) region, the designed sensor exhibits strong birefringence, supporting two separate resonance peaks in orthogonal polarizations. Results show that x-polarized resonance peak can provide much better signal to noise ratio (SNR), wavelength and amplitude sensitivities than y-polarized, which is more suitable for tempertature detecting. The graphene-Ag composite nanowire filled into the hollow fiber core can not only solve the oxidation problem but also avoid the metal coating. A wide temperature range from 22 ∘C to 47 ∘C with steps of 5 ∘C is calculated and the temperature sensitivities we obtained are 9.44 nm/ ∘C for x-polarized and 5.33 nm/ ∘C for y-polarized, much higher than other sensors of the same type.

Photonic crystal fiber-based surface plasmon resonance sensor with selective analyte channels and graphene-silver deposited core

We propose a surface plasmon resonance (SPR) sensor based on photonic crystal fiber (PCF) with selectively filled analyte channels. Silver is used as the plasmonic material to accurately detect the analytes and is coated with a thin graphene layer to prevent oxidation. The liquid-filled cores are placed near to the metallic channel for easy excitation of free electrons to produce surface plasmon waves (SPWs). Surface plasmons along the metal surface are excited with a leaky Gaussian-like core guided mode. Numerical investigations of the fiber's properties and sensing performance are performed using the finite element method (FEM). The proposed sensor shows maximum amplitude sensitivity of 418 Refractive Index Units (RIU-1) with resolution as high as 2.4 × 10(-5) RIU. Using the wavelength interrogation method, a maximum refractive index (RI) sensitivity of 3000 nm/RIU in the sensing range of 1.46-1.49 is achieved. The proposed sensor is suitable for detecting various high RI chemicals, biochemical and organic chemical analytes. Additionally, the effects of fiber structural parameters on the properties of plasmonic excitation are investigated and optimized for sensing performance as well as reducing the sensor's footprint.

Review of plasmonic fiber optic biochemical sensors: improving the limit of detection

This paper presents a brief overview of the technologies used to implement surface plasmon resonance (SPR) effects into fiber-optic sensors for chemical and biochemical applications and a survey of results reported over the last ten years. The performance indicators that are relevant for such systems, such as refractometric sensitivity, operating wavelength, and figure of merit (FOM), are discussed and listed in table form. A list of experimental results with reported limits of detection (LOD) for proteins, toxins, viruses, DNA, bacteria, glucose, and various chemicals is also provided for the same time period. Configurations discussed include fiber-optic analogues of the Kretschmann-Raether prism SPR platforms, made from geometry-modified multimode and single-mode optical fibers (unclad, side-polished, tapered, and U-shaped), long period fiber gratings (LPFG), tilted fiber Bragg gratings (TFBG), and specialty fibers (plastic or polymer, microstructured, and photonic crystal fibers). Configurations involving the excitation of surface plasmon polaritons (SPP) on continuous thin metal layers as well as those involving localized SPR (LSPR) phenomena in nanoparticle metal coatings of gold, silver, and other metals at visible and near-infrared wavelengths are described and compared quantitatively.

Surface plasmon resonance temperature sensor based on photonic crystal fibers randomly filled with silver nanowires

We propose a temperature sensor design based on surface plasmon resonances (SPRs) supported by filling the holes of a six-hole photonic crystal fiber (PCF) with a silver nanowire. A liquid mixture (ethanol and chloroform) with a large thermo-optic coefficient is filled into the PCF holes as sensing medium. The filled silver nanowires can support resonance peaks and the peak will shift when temperature variations induce changes in the refractive indices of the mixture. By measuring the peak shift, the temperature change can be detected. The resonance peak is extremely sensitive to temperature because the refractive index of the filled mixture is close to that of the PCF material. Our numerical results indicate that a temperature sensitivity as high as 4 nm/K can be achieved and that the most sensitive range of the sensor can be tuned by changing the volume ratios of ethanol and chloroform. Moreover, the maximal sensitivity is relatively stable with random filled nanowires, which will be very convenient for the sensor fabrication.

Phase modulation and structural effects in a D-shaped all-solid photonic crystal fiber surface plasmon resonance sensor

We numerically investigate a D-shaped fiber surface plasmon resonance sensor based on all-solid photonic crystal fiber (PCF) with finite element method. In the side-polished PCF sensor, field leakage is guided to penetrate through the gap between the rods, causing a pronounced phase modulation in the deep polishing case. Taking advantage of these amplified phase shifts, a high-performance fiber sensor design is proposed. The significant enhancements arising from this new sensor design should lift the performance of the fiber SPR sensor into the range capable of detecting a wide range of biochemical interactions, which makes it especially attractive for many in vivo and in situ bioanalysis applications. Several parameters which influence the field leakage, such as the polishing position, the pitch of the PCF, and the rod diameter, are inspected to evaluate their impacts. Furthermore, we develop a mathematical model to describe the effects of varying the structural parameters of a D-shaped PCF sensor on the evanescent field and the sensor performance.