Analyte Refractive Index Research Articles

Colorimetric analysis of optical reflection from thin porous silicon for detection of organic liquids

A single porous silicon (PS) layer sensor structure was applied to analyze the kinetics of adsorption/desorption processes of water, ethanol and ethanol-water solution using CIE1931 chromaticity coordinates based parameters such as dominant wavelength λdom, complementary wavelength λcom and excitation purity (EP). Matrix method was used to obtain reflectance spectra dependences on porosity (P), PS layer thickness (LPS), refractive index of analyte (nanalyte). Dependences of λdom, λcom, EP on P, LPS, nanalyte were computed on the base of computed reflectance spectra, and optimal parameters were determined for distinction of model analytes such as water and ethanol. Time dependences of λdom, λcom were experimentally obtained using CCD-based spectrometer for water, ethanol and ethanol-water solution. Advantage of characterisation of whole complex multiple peaks spectra using chromaticity parameters as opposed to sensor characterization with parameters of individual interference peaks as peak position was demonstrated.

Investigation of wide-range refractive index sensor based on asymmetric metal-cladding dielectric waveguide structure

A refractive index (RI) sensor based on an asymmetric metal-cladding dielectric waveguide structure, in which an analyte is used as the guiding layer, is proposed in this report. The angular scanning attenuated total reflection spectra of the sensor and optical field distributions under waveguide mode resonance conditions were simulated, which confirmed that multiple waveguide modes can be used for sensing, and that different waveguide modes exist in different analyte RI ranges. The curves of both waveguide mode resonance angles and the sensitivity as a function of the analyte RI demonstrated that a wide sensing range can be achieved by combining waveguide modes of different orders. The proposed sensor could be applied to numerous fields, such as biological and chemical detection.

Analysis of Dual-Core Photonic Crystal Fiber Based on Surface Plasmon Resonance Sensor with Segmented Silver Film

A dual-core photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) sensor with segmented silver film (silver nanoslit) deposited in microfluidic channel is designed. The coupling characteristics and sensing performance of the proposed sensor are analyzed numerically by finite element method (FEM). The resonance intensity and wavelength sensitivity can be tuned by the segmented number and angle of the silver nanoslit, due to a strong coupling between propagation surface plasmon resonance (PSPR) on the silver film surface and local surface plasmon resonance (LSPR) at the silver nanoslit. When the segmented number is 40 and the segmented angle is 0.5°, an average sensitivity of 5100 nm/RIU is obtained in the refractive index (RI) range from 1.330 to 1.360, and is 1080 nm/RIU higher than that of continuous silver film structure under the same conditions. In addition, a maximum wavelength sensitivity of 7600 nm/RIU is achieved in the RI range from 1.355 to 1.360, corresponding to a high RI resolution of 1.32 × 10−5 RIU, which can be used to detect the slight change in the RI of an unknown analyte.

Refractive Index Sensor Based on Micro- Structured Optical Fibers with Using Finite Element Method

In this paper a refractive index sensor based on micro-structured optical fiber has been proposed using Finite Element Method (FEM). The designed fiber has a hexagonal cladding structure with six air holes rings running around its solid core. The air holes of fiber has been infiltrated with different liquids such as water , ethanol, methanol, and toluene then sensor characteristics like ; effective refractive index , confinement loss, beam profile of the fundamental mode, and sensor resolution are investigated by employing the FEM. This designed sensor characterized by its low confinement loss and high resolution so a small change in the analyte refractive index could be detect which is could be useful to detect the change of the information of the biological molecule reaction and also in medical applications in fields like toxins, drug residues, vitamins, antibodies, proteins and parasites.

Ultra Sensitive Nonlinear Fiber Optics-Based Refractive Index Sensor Using Degenerate Four Wave Mixing Technique in Photonic Crystal Fiber

By using degenerate four wave mixing (DFWM) analysis, we proposed a refractive index (RI) sensor in photonic crystal fiber. This novel nonlinear fiber optics-based RI sensor works on the basis of Stokes and anti-Stokes photons shift, through DFWM technique under the influence of fourth-order dispersion. Here, the frequency shift of generated photons, as a response to change in the analyte RI, is analyzed using an appropriately modified nonlinear Schrodinger equation. Sensitivity of the proposed sensor is well optimized by tuning the pump wavelength and the pump power. Finally, we achieve a maximum sensitivity of −10 200 nm/RIU for anti-Stokes shift and 56 200 nm/RIU for Stokes shift, respectively, with lattice pitch of 2.94- and 1.205- $\mu \text{m}$ diameter of the airhole and 1.5-kW pump power at the pumping wavelength of 1064.7 nm, which proves it to be an advancement in the field of biomedical and chemical applications.

Ultra-stable D-shaped Optical Fiber Refractive Index Sensor with Graphene-Gold Deposited Platform

In this paper, we demonstrate a high sensitivity refractive index (RI) sensor with D-shaped structure covered with gold and graphene film. Specifically, the effect of structural parameters on the stability of fiber sensor is analyzed. In our research, it have been found that the sensor we proposed is not very sensitive to the change of structure parameters on the premise of ensuring the sensing precision. This advantage means that the requirements for machining errors are reduced. Further probing shows that the proposed sensor shows a maximum wavelength interrogation sensitivity of 4391nm/RIU with the dynamic refractive index range from 1.33 to 1.39 and a maximum amplitude sensitivity of 1139RIU− 1 with the analyte RI = 1.38 in the visible region. The corresponding resolution are 2.28 × 10− 5 and 8.78 × 10− 6 based on the methods of wavelength interrogation and amplitude-(or phase-) based method. These characteristics of compact sensing architectures, simple to fabricate, and high sensitivity open the possibility of using this type of sensor in biological applications.

Design Two Dimensional Nanocavity Photonic Crystal Biosensor Detection in Malaria

In this paper we design a two dimensional (2-D) photonic crystal based biosensor implemented by linear waveguide and nanocavity detection in malaria. The bio molecules such as a red blood cell, infected red blood cell, trapped inside the nanocavity cause transmission shift at the output terminal. The sensing mechanism of biosensor is change in refractive index of analytes. The layout biosensor is consists a linear waveguide with a nanocavity in square symmetry For the proposed photonic based biosensor, the band gap from 2210nm to 1420 nm and input wavelength of 1550nm are used in this design. The simulation results have analysed by using the finite difference time domain (FDTD) method, bandgap calculation is performed using plane wave expansion method.

Design of MO-SPR sensor element with photonic crystal

Magneto-plasmonic response in planar multilayer with prism coupling composed from Fe/Au bi-layer supplied by photonic crystal (Ta2O5 / SiO2 bi-layers) is studied. Modeled structure is intended as a sensor unit combining magneto-optical (MO) and surface-plasmon-resonance (SPR) effects. The sensitivity of MO-SPR system by small variations of analyte refractive index is tested to obtain optimal resolution ability. The non-reciprocal MO-SPR response is studied by means of the function ρ(φ) = (Rp(+) − Rp(−))/(Rp(+) + Rp(−)), where the reflectance Rp depends on the incidence angle φ and external magnetic field orientation by a fixed wavelength. The detection ability is characterized by the angular shift Δφ0 between the null-points of the function ρ that corresponds to the change Δna of analyte refractive index. Besides the key role of metallic layers thicknesses the number and size of Ta2O5/SiO2 bi-layers of photonic crystal are discussed. The magneto-plasmonic response in planar multilayer with prism coupling composed from Fe and Au bilayer supplied by photonic crystal (Ta2O5 / SiO2) is studied. Modeled structure is intended as a sensor unit combining MO and SPR effects.

Refractive index sensing using a light trapping cavity: A theoretical study

A refractive index sensor is proposed comprising one-dimensional photonic bandgap geometry in conjunction with a thin metal film. The refractive index sensor is based on the cavity mode formed in a thin cavity layer sandwiched between multilayers of SiO2/Ta2O5 and a metal film. The cavity structure traps light through excitation of the cavity mode and hence sharp resonance minima (maxima) are obtained in the reflection (transmission) spectrum. Our theoretical model investigates the impact of cavity thickness, nature of plasmon-active metal, the angle of incidence, and polarization of light on the sensitivity. It is found that the resonance wavelength increases linearly as the analyte refractive index increases. Additionally, the enhancement in the interaction between the analyte medium and micro-cavity mode-field further enhances the sensitivity of the proposed sensor. It is observed that as the cavity thickness increases from 200 nm to 900 nm, the sensitivity increases from 200 nm/RIU to 350 nm/RIU. The performance of the proposed photonic crystal based sensor exhibits strong polarization and angular dependences. Also, the sharp micro-cavity resonance results in improved detection accuracy as compared to surface plasmon resonance based schemes. The proposed structure advantage is an alternative to the conventional surface plasmon refractive index sensor.

Dual core photonic crystal fiber based surface plasmon resonance biosensor

This article proposed a dual core photonic crystal fiber (DC-PCF) biosensor based on surface plasmon resonance (SPR). The finite element method (FEM), wavelength and amplitude interrogation methods are used to analyze the performance of the proposed sensor. The maximum wavelength sensitivity of 9000 nm/RIU and 25,000 nm/RIU, with analyte refractive index (RI) of 1.38, are numerically achieved for x-and y-polarized modes, respectively. Besides that, the structure shows the maximum amplitude sensitivity of around 470 RIU−1 and resolution as high as 1.11 × 10−5 RIU ∼4 × 10−6 RIU for both polarizations. Therefore, the proposed high sensitive biosensor can be useful in different wavelength ranges for the simultaneous detection of biological and biochemical analytes.

Photonic crystal-based optical biosensor: a brief investigation

In this paper, a two-dimensional photonic crystal biosensor for medical applications based on two waveguides and a nanocavity was explored with different shoulder-coupled nanocavity structures. The most important biosensor parameters, like the sensitivity and quality factor, can be significantly improved. By injecting an analyte into a sensing hole, the refractive index of the hole was changed. This refractive index biosensor senses the changes and shifts its operating wavelength accordingly. The transmission characteristics of light in the biosensor under different refractive indices that correspond to the change in the analyte concentration are analyzed by the finite-difference time-domain method. The band gap for each structure is designed and observed by the plane wave expansion method. These proposed structures are designed to obtain an analyte refractive index variation of about 1–1.5 in an optical wavelength range of 1.250–1.640 µm. Accordingly, an improved sensitivity of 136.6 nm RIU−1 and a quality factor as high as 3915 is achieved. An important feature of this structure is its very small dimensions. Such a combination of attributes makes the designed structure a promising element for label-free biosensing applications.

Multiple plasmonic resonance excitations on graphene metamaterials for ultrasensitive terahertz sensing

A three-dimensional graphene metamaterial structure consisting of dielectric pillar arrays covered by graphene monolayer with metal layer underneath is proposed and investigated, which can realize the efficient excitations of multiple plasmonic resonance modes under incident terahertz (THz) wave. The multiple plasmonic resonance modes are highly sensitive to the change of analyte refractive index and thickness, and the frequency sensitivity of each resonance mode can reach up to 1.402, 1.687 and 1.643 THz per refractive index unit, respectively. By controlling the Fermi level of graphene, the resonance frequency can be tuned dynamically. Moreover, the proposed structure has three absorption peaks with absorptivity more than 95%, it is polarization-insensitive and can perform very well in a wide incident angles for transverse electric and transverse magnetic waves. This proposed structure can be utilized for active THz plasmonic devices such as multiple channel sensors and absorbers.

Numerical modelling of light propagation in surface plasmon resonance sensor with liquid crystal

The five-layer nanorod-mediated surface plasmon sensor with inhomogeneous liquid crystal layer was theoretically investigated. The reflectance as the function of the incident angle was calculated at different voltages applied to the liquid crystal (LC) for different analyte refractive indices. By changing the LC director orientation one can control the position of the reflective dips and choose the one that is the most sensitive to the analyte refractive index. At the chosen angle of incidence, the analyte refractive index can be found from the reflectance value. The director reorientation effect is stronger when the prism refractive index is between ordinary and extraordinary refractive indices of the LC. In this case, the voltage increase and the prism refractive index decrease have a similar effect on the reflectance features.

Highly sensitive photonic crystal fiber biosensor based on titanium nitride

A highly sensitive surface plasmon resonance photonic crystal fiber (PCF) biosensor based on Titanium Nitride (TiN) as a new alternative plasmonic material is proposed and analyzed. The TiN has high stability, high conductivity, and corrosion resistance which make it an ideal material for nanofabrication. The suggested biosensor is analyzed by full vectorial finite element method with perfectly matched layer as boundary conditions. In this paper, the biosensor geometrical parameters are studied to achieve high sensitivity for both polarized modes. A refractive index sensitivity of 7700 and 3600 nm/RIU for quasi-transverse electric and quasi transverse magnetic modes, respectively, are obtained. Additionally, the reported biosensor could be used for detecting an unknown analyte refractive index ranging from 1.32 to 1.34 with a high linearity. Further, the proposed biosensor structure is easy for fabrication using standard PCF fabrication current technologies.

Sensitive detection of cancer cell apoptosis based on the non-bianisotropic metamaterials biosensors in terahertz frequency

The apoptosis of cancer cells was experimentally measured by terahertz (THz) biosensors based on the metamaterials (MMs). The non-bianisotropic resonance with an electric field of up to 106 V/m was exhibited at 0.85 THz, where the magnetic dipoles were cancelled in the unit cell. The simulate results show the dependence of the frequency shift on the occupying ratio and refractive index of analytes. The theoretical sensitivity was calculated to 182 GHz/RIU. The experimental results imply that the resonant frequency would red shift with the increase of the concentration of cancer cells. Furthermore, the apoptosis of cancer cells HSC3 under the effect of drug concentration from 1 to 15 μM and drug action time from 24 to 72 hours were also studied by the biosensors, respectively. It shows that the trend agrees with the results measured by the biological CCK-8 kits method. Our proposed MMs-based biosensors may supply a novel viewpoint on cell apoptosis from a physical perspective and be a valuable complementary reference for biological study.

Highly sensitive selectively coated photonic crystal fiber-based plasmonic sensor.

Highly sensitive and miniaturized sensors are highly desirable for real-time analyte/sample detection. In this Letter, we propose a highly sensitive plasmonic sensing scheme with the miniaturized photonic crystal fiber (PCF) attributes. A large cavity is introduced in the first ring of the PCFs for the efficient field excitation of the surface plasmon polariton mode and proficient infiltration of the sensing elements. Due to the irregular air-hole diameter in the first ring, the cavity exhibits the birefringence behavior which enhances the sensing performance. The novel plasmonic material gold has been used considering the chemical stability in an aqueous environment. The guiding properties and the effects of the sensing performance with different parameters have been investigated by the finite element method, and the proposed PCFs have been fabricated using the stack-and-draw fiber drawing method. The proposed sensor performance was investigated based on the wavelength and amplitude sensing techniques and shows the maximum sensitivities of 11,000nm/RIU and 1,420 RIU-1, respectively. It also shows the maximum sensor resolutions of 9.1×10-6 and 7×10-6 RIU for the wavelength and amplitude sensing schemes, respectively, and the maximum figure of merits of 407. Furthermore, the proposed sensor is able to detect the analyte refractive indices in the range of 1.33-1.42; as a result, it will find the possible applications in the medical diagnostics, biomolecules, organic chemical, and chemical analyte detection.

Surface Plasmon Resonance Sensor Based on a Novel D-Shaped Photonic Crystal Fiber for Low Refractive Index Detection

A novel D-shaped photonic crystal fiber refractive index sensor based on surface plasmon resonance (SPR) is proposed and numerically studied. Different from the normal D-shaped structures, we here used an open-ring channel coated with gold film to excite the plamonic modes. The coupling properties and sensing performance of this structure are analyzed using finite element method. Simulation results indicate that the sensor has a sensing range from 1.20 to 1.29. When the analyte refractive index (RI) is above 1.25, the anti-crossing effect starts to appear, and the peak loss of the loss spectra remains nearly constant with increasing RI. The maximum spectral sensitivity of 11055 nm/RIU and high resolution of $9.05\times 10^{-6}$ RIU can be obtained at 1.29. For the purpose of optimizing sensing performance, the effects of the structure parameters on the resonant spectra are also studied. The excellent sensing performance makes the proposed SPR sensor a competitive candidate in low refractive index detection applications.

Tuning the Resonance of the Excessively Tilted LPFG-Assisted Surface Plasmon Polaritons: Optimum Design Rules for Ultrasensitive Refractometric Sensor

An excessively tilted LPFG-assisted surface plasmon polaritons sensor (Ex-TLPFG assisted SPP sensor) with ultrahigh sensitivity is proposed and numerically investigated using the finite-element-method-based full-vector complex coupled mode theory. We show that the SPP mode is transited (or excited) gradually from both the p-polarized TM $_{0,j}$ and EH $_{v,j}$ ( $v\geq 1$ ) modes, and hence, the proposed SPP sensor can be tuned to achieve strong resonance of either the degenerate TM $_{0,j}$ and EH $_{2,j}$ modes or EH $_{1,j}$ mode to optimize the sensitivity for analyte refractive index sensing. The results confirm that a transition point corresponding to the phase matching curve of the SPP mode is obtained, which can be used to predict the optimized grating period. By this approach, ultrasensitive SPP refractometric sensor can be obtained and the sensitivity can be further improved through a simple method: reducing the fiber cladding combined with an optimized grating period. We demonstrate that a giant sensitivity as high as $10100\,\text{nm}/\text{RIU}$ is achieved for the degenerate TM $_{0,32}$ and EH $_{2,32}$ modes (or $7400\,\text{nm/RIU}$ for the EH $_{1,32}$ mode). These appealing characteristics make the proposed Ex-TLPFG-assisted SPP sensor ideal for biochemical analyte sensing applications.

Silver layer thickness insensitive index sensor based on hollow core photonic crystal fiber

We propose a silver layer thickness insensitive index sensor based on silver coated on the inner wall of the HC-PCF. Under the boundary condition of anisotropic perfectly matched layer (PML), a full-vector finite element method (FEM) is used to calculate the fiber model. Numerical results indicate that the excitation of the plasmon mode is sensitive to the change of the refractive index of the adjacent analyte. The confinement loss of the core guided mode increases when both the refractive index of the analyte and the thickness of the silver film do. The maximum spectral sensitivity of the sensor can be 7330 nm/RIU. Furthermore, the spectral sensitivity of the sensor doesn’t approximately change when the thickness of the silver film increases.

Hollow-core silver coated photonic crystal fiber plasmonic sensor

We propose a simple hollow-core circular lattice photonic crystal fiber (PCF) based surface plasmon resonance (SPR) refractive index sensor. The sensing performance is investigated by using the finite element method (FEM). Silver is used as the plasmonic material for this design, which is placed on the outer surface of the PCF to facilitate the fabrication. The proposed sensor shows a maximum wavelength sensitivity of 4200 nm/RIU with a sensor resolution of 2.38 × 10−5 RIU. Besides, a maximum amplitude sensitivity of 300 RIU−1 and a resolution of 3.33 × 10−5 RIU is reported for an analyte refractive index of 1.37. Moreover, the effect of varying structural parameters on the sensing performance such as pitch, air hole diameter and silver layer thickness are also discussed thoroughly. Sensitivity analysis of the proposed sensor is performed in order to investigate the impact on loss depth and amplitude sensitivity. Thanks to high sensitivity and linearity characteristics, the proposed sensor can be potentially employed in practical bio-sensing and chemical sensing applications.