Refractive Index Detection Research Articles

Dual-channel high sensitivity photonic crystal fiber sensor based on rectangular air holes

This paper proposes a dual-channel high sensitivity photonic crystal fiber sensor with rectangular air holes, which can detect the refractive index of a single sample or detect the refractive index of two samples simultaneously, to increase the detection efficiency and wavelength sensitivity of the sample refractive index. The sensor can reduce the times of filling, emptying and cleaning of the sample to be tested and save labor and time costs. The finite element method is used to thoroughly analyze the proposed structure’s sensing properties. The results show that when the sensor detects a single sample, the maximum wavelength sensitivity is 67,300[Formula: see text]nm/RIU, and the highest figure of merit (FOM) is 547 RIU[Formula: see text]. When the sensor detects two samples synchronously, the maximum wavelength sensitivity is 64,100[Formula: see text]nm/RIU, which is the highest level among the known sensors of the same kind. It has good application prospect in the field of high sensitivity refractive index detection.

Characterization of incompletely coated D-shaped PCF-SPR refractive index sensors

To reduce the complexity of the sensor structure and improve the sensitivity of refractive index (RI) measurement, a D-shaped photonic crystal fiber (PCF) surface plasmon resonance (SPR) RI sensor with incomplete coating of gold-tantalum pentoxide (Au-Ta2O5) on the surface is proposed. When the coating width is 3.1 μm, the sensor can detect RI samples ranging from 1.35 to 1.41 in the ultra-wide near-infrared (NIR) region of 1100–2100 nm wavelength. Its maximum wavelength sensitivity is 20,000 nm RIU−1, maximum amplitude sensitivity is 2817.7 RIU−1, resolution is RIU, and figure of merit (FOM) is 333.3 RIU−1. This sensor can be widely used in biological tissue detection. For this type of incomplete coated D-shaped sensor, the coating material and structural parameters not only affect the performance of the sensor, but also change the RI detection range, which has been ignored or not mentioned in previous literature on PCF-SPR sensors. Therefore, the reasons for the change of RI detection interval and negative optimization caused by structural parameters were analyzed, and two different sensors with different coating widths were finally obtained, which can achieve high sensitivity sensing in their respective detection intervals. The detailed research results expand the understanding of the SPR phenomenon in D-shaped PCF and provide theoretical guidance for adjusting and improving the detection performance of PCF-SPR sensors.

Highly sensitive refractive index, chemical potential, and applied electrical voltage detection in terahertz region with photonic spin Hall effect in a plasmonic sensor based on graphene and germanium layers

"In this work, a transverse spin-dependent shift (SDS) of the horizontal photonic spin Hall effect (PSHE) at a fixed frequency (5 THz) is simulated for detection of refractive index, chemical potential, and applied electrical voltage to a plasmonic sensor with four layers (germanium, organic layer, graphene, and gas medium). The variation of the refractive index of graphene with chemical potential and applied voltage is given from the simulated values. A refractive index resolution (1.73 × 10–12 RIU) is obtained when the refractive index n4 of the analyte layer is changed from 1 RIU to 1.1 RIU when the chemical potential μc is 0.003 eV and the amplified angle ∆ is 0.1°. A chemical potential resolution (6.32 × 10–14 eV) and corresponding voltage resolution (6.83 × 10–13 V) are obtained when the chemical potential is changed from 0.003 eV to 0.03 eV, the refractive index of gas medium n4 is 1.1 RIU and the amplified angle is ∆ = 0.1°. These values are very good in comparison with the situation when the spin Hall effect is not applied (7.47 × 10–6 RIU, 0.001166 eV, and 0.01259 V) for the same values of μc, n4, and ∆."

Low-loss and high-sensitivity surface plasmon resonance sensor composed of microstructured optical fibers for wide visible-to-infrared and refractive index ranges

ObjectiveOptical fiber sensing technology develops rapidly and is widely used. In order to design a SPR sensor with better performance and easy production, a new type D-MOF sensor with low loss, high sensitivity and simple structure is proposed. MethodsThe full vector finite element method (FEM) was used to optimize the structure parameters by using the multi-physics analysis software COMSOL, and the performance of the structure was systematically analyzed. ResultsThe sensor operational wavelength spans the visible and infrared range (430 nm to 7200 nm). The refractive index detection range of 1.00–1.42, the maximum wavelength sensitivity and the optimal resolution are 60,000 nm/RIU and 1.67 × 10−6 RIU−1, respectively, and the maximum limiting loss peak is 64.99 dB/cm. In addition, MOF-SPR sensors have large tolerance and low sensitivity of structural parameters in actual manufacturing. It has great application potential in biosensing and other fields.

Development of surface plasmon resonance sensor with enhanced sensitivity for low refractive index detection

Development of surface plasmon resonance sensor with enhanced sensitivity for low refractive index detection

Refractive index SPR sensor with high sensitivity and wide detection range using tapered silica fiber and photopolymer coating.

This paper introduces a surface plasmon resonance (SPR) sensor using tapered silica fiber and photopolymer coating for enhanced refractive index (RI) detection. Tapering the silica fiber to a diameter of 10 µm ensures the evanescent wave leaks into a 1.8-µm thick photopolymer film, which increases the average waveguide RI and broadens the RI detection range accordingly. A 50-nm thick single-side gold film is coated on the photopolymer film, exciting SPR and causing less light transmission loss than a double-side gold film. The method avoids the complex microfabrication processes of conventional polymer optical fiber SPR sensors, while the waveguide RI can be controlled by altering the curing time of the photopolymer during fabrication. The sensor has an overall sensitivity of 3686.25 nm/RIU, enabling RI detection of 1.333 - 1.493. Moreover, the sensor has an ultrahigh sensitivity of 6422.9 nm/RIU in the RI range of 1.423 - 1.493. The temperature response is about 1.43 nm/°C at 20 - 50 °C, which has little impact on RI detection. Finally, we demonstrate that the sensor can grade the severity of hepatic steatosis by measuring the RIs of cytoplasm/triglyceride emulsions with superior sensing performance.

Development and Validation of a Method for Trace Level Zinc Quantification in Pharmaceutical Zinc Supplements Using a Carboxyl Functional Group Packed Column and Refractive Index Detector.

Zinc helps with cell division, growth, wound healing, and carbohydrate breakdown. Humanbeings have to obtain zinc from food or supplements because our bodies do not produce it naturally. In view of the greater advantages (such as low cost, time of analysis, and stability-indicating) compared to other quantification methods (titration, ion chromatography, Atomic absorption spectroscopy) proposed in the literature, a refractive index detector coupled with HPLC has been used in quantification of zinc. The goal of this research is to develop and validate a sensitive, low-cost, high-resolution, and stability- indicating method for detecting and quantifying zinc levels in zinc supplement pharmaceutical products (injectables, tablets, and capsules). A novel isocratic reverse-phase HPLC method with a refractive index detector (with sensitivity 64, detector temperature 35°C, and positive polarity) was developed using a carboxyl functional group packed column and 0.8% (v/v) formic acid as the mobile phase to detect and quantify zinc content. The reported method has a good optimal sensitivity (LOQ: 0.006 mg/mL and LOD: 0.002 mg/mL). The correlation coefficient (r) obtained from the zinc calibration plot was greater than 0.998, indicating that the method was linear and that there was a strong correlation between zinc concentration (0.006 mg/mL to 0.375 mg/mL) and peak response. The accuracy at LOQ level was found to be 95-105% and 97-103% at the remaining levels (50, 100, and 150%). The proposed method was successfully developed and validated as per International council for harmonisation (ICH) guidelines. Therefore, this method can be used for the quantitative testing of zinc in the QC laboratory. A novel method was developed for zinc levels determination in pharmaceutical products using HPLC with a refractive index detector. The present approach has a quick run time of 10 min and is inexpensive.

Dual-band complementary metamaterial perfect absorber for multispectral molecular sensing.

Metamaterial perfect absorbers (MPAs) show great potential in achieving exceptional sensing performance, particularly in the realm of surface-enhanced infrared absorption (SEIRA) spectroscopy. To this aim, it is highly desirable for the localized hotspots to be readily exposed and accessible to analyte with strong mode confinement to enhance absorption. Here, we propose a quasi-three-dimensional MPA based on cross-shaped coupled complementary plasmonic arrays for highly sensitive refractive index sensing and molecular vibrational sensing. Dual-band perfect absorption can be approached with the two plasmonic resonances corresponding to the electric dipole-like mode of cross antenna array and the magnetic dipole-like mode of cross hole array, respectively. Large portions of the electric field of the hotspots are exposed and concentrated in the gap between the elevated cross antenna and its complementary structure on the substrate, leading to improved sensing sensitivities. An ultrathin polymethyl methacrylate (PMMA) film induces a significant redshift of the magnetic dipole-like mode with an 11.8 nm resonance shift per each nanometer polymer thickness. The value is comparable to the reported sensitivity of single molecule layer sensors. Additionally, the simultaneous detection of the C = O and C-H vibrations of PMMA molecules is enabled with the two plasmonic resonances adjusted by changing the lengths of the two cross branches. Remarkably, the observed mode splitting and anti-crossing behavior imply the strong interaction between plasmonic resonance and molecular vibration. Our dual-band MPA based on coupled complementary plasmonic arrays opens a new avenue for developing highly sensitive sensors for the detection of refractive index and multispectral molecular vibrations.

Production, Characterization and Prebiotic Potential of Xylooligosaccharides Produced from Wheat Bran using Enterobacter hormaechei KS1 Xylanase.

In the present investigation, xylooligosaccharides were produced from wheat bran and wheat bran extracted xylan through enzymatic hydrolysis using xylanase from novel Enterobacter hormaechei KS1. Xylooligosaccharides/reducing sugars production from wheat bran was found maximum (374mg/g) when 4.0% of wheat bran was treated with 375 units (IU/mL) of Enterobacter hormaechei KS1 xylanase at pH 6.0 and incubated at 50°C for 24h of incubation. In case of wheat bran extracted xylan 419mg/g of xylooligosaccharides were produced when 3% of extracted xylan was incubate for 8h. Analysis of the enzymatic hydrolysate through high performance liquid chromatography equipped with refractive index detector showed the presence of xylose, xylopentose and xylohexose. The decrease in pH with 1.0% dose of xylooligosacchaides produced from extracted xylan hydrolysis using E. hormaechei KS1 xylanase showed more decrease with L. rhamnosus (6.72 to 5.94) followed by L. brevis (6.71 to 6.15) and L. plantarum (6.71 to 6.41). In case of increase in optical density both wheat bran and wheat bran extracted xylan generated xylooligosaccharides exhibited similar pattern i.e., L. rhamnosus > L. plantarum > L. brevis.

Enhanced sensitivity and wide refractive index detection range of D-shaped SPR fiber sensor based on Au/ZnO nanostructures

Enhanced sensitivity and wide refractive index detection range of D-shaped SPR fiber sensor based on Au/ZnO nanostructures

A high-sensitivity D-shaped photonic crystal fiber surface plasmon resonance sensor for low refractive index detection

A high-sensitivity D-shaped photonic crystal fiber surface plasmon resonance sensor for low refractive index detection

A Liquid Crystal-Modulated Metastructure Sensor for Biosensing.

In this paper, a liquid crystal-modulated metastructure sensor (MS) is proposed that can detect the refractive index (RI) of a liquid and change the detection range under different applied voltages. The regulation of the detection range is based on the different bias states of the liquid crystal at different voltages. By changing the sample in the cavity that is to be detected, the overall electromagnetic characteristics of the device in the resonant state are modified, thus changing the position of the absorption peaks so that different RI correspond to different absorption peaks, and finally realizing the sensing detection. The refractive index unit is denoted as RIU. The range of the refractive index detection is 1.414-2.828 and 2.121-3.464, and the corresponding absorption peak variation range is 0.8485-1.028 THz and 0.7295-0.8328 THz, with a sensitivity of 123.8 GHz/RIU and 75.6 GHz/RIU, respectively. In addition, an approach to optimizing resonant absorption peaks is explored, which can suppress unwanted absorption generated during the design process by analyzing the energy distribution and directing the current flow on the substrate. Four variables that have a more obvious impact on performance are listed, and the selection and change trend of the numerical values are focused on, fully considering the errors that may be caused by manufacturing and actual use. At the same time, the incident angle and polarization angle are also included in the considered range, and the device shows good stability at these angles. Finally, the influence of the number of resonant rings on the sensing performance is also discussed, and its conclusion has guiding value for optimizing the sensing demand. This new liquid crystal-modulated MS has the advantages of a small size and high sensitivity and is expected to be used for bio-detection, sensing, and so on. All results in this work were obtained with the aid of simulations based on the finite element method.

Reflector-less refractive index sensors based on etched-tapered high-scattering single-mode optical fibers

Reflector-less refractive index (RI) sensors employ simple optical fiber strictures for the accurate detection of RI changes. They operate in absence of any reflective element such as gratings, filters, interferometers while maintaining the form factor of a reflective probe; the RI dependence is encoded in the Rayleigh backscattering signatures, and is interrogated using optical backscatter reflectometry. In this work, we present a new reflector-less fiber-optic sensor based on two-steps: (1) tapering an optical fiber, followed by (2) rapid etching of the fiber. The combination of the two steps allows obtaining significant advantages in terms of manufacturing, making the process simpler and increasing the distribution of the refractive index detection. The sensitivity obtained is up to 110.9 GHz/RIU (refractive index units), with the possibility of detection over a length of 2.1 mm, with 0.035 mm average spatial resolution over distributed RI sensing.

Simultaneous Detection of Temperature, Strain, Refractive Index, and pH Based on a Phase-Shifted Long-Period Fiber Grating

A novel π-phase-shifted (PS) long-period fiber-grating (LPFG) sensor operating near the phase-matching turning point (PMTP) was proposed. The PS-LPFG sensor can simultaneously detect temperature, strain, refractive index (RI), and pH. Due to the introduction of π phase shift, the double resonance peak of the selected cladding mode was divided into four loss peaks, which is convenient for multiparameter measurement. By monitoring the resonant-wavelength shifts of four dips of PS-LPFG, simultaneous detection of temperature, strain, RI, and pH can be achieved. Moreover, using a simple LPFG design on one fiber and a multiparameter matrix algorithm, the crosstalk between multiple signals was eliminated. Graphene oxide/polyvinyl alcohol (GO/PVA) hydrogel was coated onto the grating sensing area to measure the change in pH, and the sensitivity was higher than that of the same type of fiber-grating sensor. Results showed that the maximum sensitivity of temperature, strain, RI, and pH of the fabricated phase-shifted grating sensing structure were 0.2128 nm/°C, 0.1225 nm/μϵ, 718 nm/RIU, and -1.0166 nm/pH, respectively. Overall, the proposed sensor had great potential applications in monitoring marine environments and biochemistry sensing.

Separation and characterization of Gastrodia elata polysaccharides based on asymmetrical flow field-flow fractionation: steric transition phenomenon

Asymmetrical flow field-flow fractionation (AF4), a gentle tool for the separation and characterization of particles and macromolecules, has attracted increased interest in recent years owing to its broad dynamic size range and utilization of "open channel" voids in the packing or stationary phase. A steric transition phenomenon in which the sample elution mode change from the normal mode to the steric/hyperlayer mode occurs. Accurate characterization by AF4 requires the absence of steric transition, particularly when the sample has a broad size distribution, because the effect of the combination of different modes is difficult to interpret. In this study, the relative molecular mass (M), radius of gyration (Rg), and conformation of Gastrodia elata polysaccharides (GEPs) were characterized using AF4 coupled with online multi-angle light scattering (MALS) and differential refractive index (dRI) detection (AF4-MALS-dRI). Steric transition was observed during GEP separation by AF4 owing to the broad size distribution of the molecules. This phenomenon would result in the inaccurate characterization of the GEPs in terms of M and Rg because two GEP groups of different sizes may elute together. In this study, the effects of constant and exponentially decaying cross-flow rates, sample mass concentration, and spacer thickness on steric transition were systematically investigated. The results indicated that a high GEP mass concentration (i. e., 0.75 mg/mL) can lead to steric transition. The spacer thickness affected the resolution and retention time of the GEPs and changed the steric transition point (di). An exponentially decaying cross-flow rate not only adjusted the di of the polydisperse GEP samples but also improved the GEP resolution and shortened the analysis time. The influence of steric transition was solved under the following operating conditions: injected GEP mass concentration=0.5 mg/mL; injection volume=50 μL; spacer thickness=350 μm; detector flow rate=1.0 mL/min; and cross-flow rate exponentially decayed from 0.2 to 0.05 mL/min with a half-life of 2 min. Moreover, the influence of GEP origins and ultrasound treatment time on the M and Rg distributions and conformation of GEPs were investigated under the optimized operating conditions. The results showed that the M and Rg distributions of Yunnan and Sichuan GEPs decreased with increasing ultrasound time. When the ultrasound treatment time was 15 min, the Yunnan GEPs had a loosely hyperbranched chain conformation, whereas the Sichuan GEPs had a spherical conformation. When the ultrasound treatment time was increased to 30 or 60 min, the GEPs from both Yunnan and Sichuan had a hyperbranched chain conformation, indicating that ultrasound treatment resulted in GEP degradation. Under the same extraction conditions, GEPs from Yunnan had larger M and Rg values than those from Sichuan. AF4-MALS-dRI showed good repeatability for the characterization of GEPs under the optimized operating conditions. The relative standard deviations of Rg and M were 0.5% and 1.7%, respectively. The data presented in this study can be used as a starting point for in-depth studies on the structural bioactivity of GEPs.

SPR Sensor Based on Cascaded NCF and U-Shaped Multimode Fibers for Simultaneous Detection of Refractive Index and Temperature

A surface plasmon resonance (SPR) sensor based on hybrid structure with cascaded no-core fiber (NCF) and U-shaped multimode fiber (MMF) for simultaneous measurement RI and temperature is proposed. One of the SPR channels excited using the U-shaped MMF coated with an Au film is employed for measuring the RI, while the other SPR channel that is excited using the NCF coated with an Au film and polydimethylsiloxane (PDMS) is used for temperature measurement at the same time. The experimental results show that an RI sensitivity of 3364 nm/RIU and temperature sensitivity of -3.26 nm/°C are achieved by using the proposed sensor. The proposed sensor offers the advantages of a compact structure and stability, making it suitable for potential applications in fields requiring multi-parameter measurements, such as environmental monitoring, drug diagnostics, and biochemical sensing.

Solution structure of bilayer membrane-embedded proton-translocating pyrophosphatase revealed via small-angle X-ray scattering

The conformations and compositions of a proton-translocating pyrophosphatase Vigna radiata H+-PPase (VrPPase), stabilized by either detergent molecules or embedded in a lipid nanodisc in aqueous solution, are revealed using size exclusion chromatography coupled small-angle X-ray scattering (SEC-SAXS) with online UV–Vis absorption and refractive index (RI) detections. The integrated analysis of the scattering and optical data indicates that the large VrPPase dimer can be embedded successfully into the POPC nanodisc, with the transmembrane region immersed into the lipid aliphatic chains. The corresponding structural parameters of the protein-nanodisc complex are determined using an analytical core-multishell elliptical cylinder model. After binding with imidodiphosphate (IDP) to mimic the substrate (PPi) binding, the VrPPase embedded in the nanodisc shows no obvious structural changes. Correspondingly, the detergent-solubilized tetramers display a relatively prominent structural response to the IDP binding. About 450 n-decyl-β-d-maltopyranoside molecules are present in the detergent corona surrounding the hydrophobic area of the protein tetramer, making it difficult to attribute the structural changes observed solely to the VrPPase. Nevertheless, the combined measurements and analysis of the SEC-SAXS advance the understanding of the two types of membrane-protein complexes in terms of their compositions and structural features.

Revealing cholesterol effects on PEGylated HSPC liposomes using AF4-MALS and simultaneous small- and wide-angle X-ray scattering.

Liposome development is of great interest owing to increasing requirements for efficient drug carriers. The structural features and thermal stability of such liposomes are crucial in drug transport and delivery. Reported here are the results of the structural characterization of PEGylated liposomes via small- and wide-angle X-ray scattering and an asymmetric flow field-flow fractionation (AF4) system coupled with differential refractive-index detection, multi-angle light scattering (MALS) and dynamic light scattering. This integrated analysis of the exemplar PEGylated liposome formed from hydrogenated soy phosphatid-yl-choline (HSPC) with the addition of cholesterol reveals an average hydro-dynamic radius (R h) of 52 nm with 10% polydispersity, a comparable radius of gyration (R g) and a major liposome particle mass of 118 kDa. The local bilayer structure of the liposome is found to have asymmetric electronic density profiles in the inner and outer leaflets, sandwiched by two PEGylated outer layers ca 5 nm thick. Cholesterol was found to effectively intervene in lipid chain packing, resulting in the thickening of the liposome bilayer, an increase in the area per lipid and an increase in liposome size, especially in the fluid phase of the liposome. These cholesterol effects show signs of saturation at cholesterol concentrations above ca 1:5 cholesterol:lipid molar ratio.

Au-NP-based colorimetric assay for sugar detection and quantification

Sugars have been associated with health problems such as metabolic syndrome, obesity, elevated triglycerides, and other features of metabolic disorders. Here, we report on the design and characterization of a highly sensitive gold nanoparticle (AuNP)-based assay for measuring sugars levels in fluids. AuNPs are functionalized with 4-mercaptobenzoic acid (4MBA) to modulate surface plasmonic resonance (SPR) frequency and fluorescent energy absorption by AuNPs, based on a fixed concentration of fluorescein introduced along with a fluid sample containing a determined quantity of sugar. We find the driving mechanism to be kinetic competition between fluorescein and saccharide which occupies the active carboxylic sites of the functional groups on the nanoparticle surface. This drives a colorimetric response in the 4MBA-AuNP solution, from orange to green, discernible to the naked eye. The aggregation of functionalized AuNPs as a result of increasing sugar concentration was confirmed via UV–vis spectroscopy and identified by a spectral peak of 620–675 nm. The limit of detection (LOD) was (55.8 ± 1.1) µM, with a highly repeatable calibration curve in the range of 0.09 – 2.45 mM. The assay's cost-effectiveness, speed, and simplicity open the door to multiple applications associated with detecting and quantifying sugars, including food science. The sensory platform was successfully tested in mixed sugar solutions to study the sensitivity capacity and applied to strawberry and kiwi freeze-dried samples. The results are validated by HPLC with refractive index detection.

High Sensitivity and Wide Range Refractive Index Sensor Based on Surface Plasmon Resonance Photonic Crystal Fiber.

In order to detect the refractive index (RI) of high refractive index materials such as trichlorobenzene and aniline in the near-infrared and mid-infrared spectra and expand the detection range of the refractive index, a surface plasmon resonance (SPR) photonic crystal fiber (PCF) sensor based on an elliptical sensing channel is proposed for high refractive index detection. The fiber core and the analyte channel are surrounded by two types of air holes with different sizes. When the surface plasmon resonance effect appears at the interface between the fiber core and the elliptical sensing layer, obvious resonance peaks appear in the near-infrared and mid-infrared bands. The full vector finite element method (FEM) is used to study the sensing characteristics of the sensor and the influence of structural parameters on the resonance peak. The results demonstrate that the sensor achieves detection in the refractive index range of 1.41-1.58, in the wavelength range of 1600-3200 nm. The average wavelength sensitivity is 9217.22 nm/RIU, and the refractive index resolution is 10.85 × 10-6 RIU. The proposed sensor realizes high refractive index detection in the near-infrared and mid-infrared bands, and obtains an ultra-wide detection range and higher sensitivity. The sensor has broad application prospects in chemical detection, biomedical sensing and other fields, and provides a theoretical reference for the design of a photonic crystal fiber surface plasmon resonance sensor.