Wavelength Interrogation Technique Research Articles

Sensitivity enhancement of the surface plasmon resonance sensor based on gallium-doped zinc oxide and silicon for cancer detection: A wavelength interrogation approach

Surface plasmon resonance (SPR) sensors have become an essential tool for the label-free and immediate detection of biomolecular interactions. This paper presents a unique method for increasing the sensitivity of an SPR sensor designed for cancer detection. We offer a sensor design that promises improved detection capabilities using the unique characteristics of silicon (Si) and gallium-doped zinc oxide (GZO). The method uses a wavelength interrogation technique to precisely monitor biomolecular interactions by taking advantage of the spectrum changes SPR brings. The sensor's potential for detecting early-stage cancer is shown by numerical findings that support a considerable improvement in sensitivity to 1711.7 nm/RIU for Basal cancer cells. A promising route for developing biological sensing technologies is the combination of GZO and Si in the SPR sensor, wavelength interrogation, transfer matrix method (TMM)-based reflectance computation, and the attenuated total reflection principle.

Highly sensitive dual core photonic crystal fiber-based LSPR sensor with simultaneous multi-analyte detection of a wide refractive index range

This manuscript introduces an anisotropic highly sensitive dual core photonic crystal fiber sensor based on localized surface plasmon resonance, possessing the ability to detect multiple analytes simultaneously. Liquid analytes having a refractive index (RI) within the range of 1.25 to 1.5 RIU have been investigated using the proposed sensor. The numerical analysis of the sensing parameters for the proposed sensor shows a maximum wavelength sensitivity of 47,500 nm/RIU for x-polarization (Channel 1) and 18,050 nm/RIU for y-polarization (Channel 2), respectively using the wavelength interrogation technique. Maximum amplitude sensitivity of 625 RIU−1 and 437 RIU−1 is obtained for x−pol. and y−pol., respectively using the amplitude interrogation technique. Maximum sensor resolution of 2.11 × 10−6 RIU and 5.01 × 10−6 RIU is obtained for x−pol. and y−pol., respectively. The linear relationship of the resonant wavelength with the RI produces R2 = 0.9976 and R2 = 0.9979, corresponding to a degree (3) for x−pol. and y−pol., respectively. The figure of merit for x−pol. and y−pol. are 84 RIU−1 and 123 RIU−1.

Low-Cost ZnO Spray-Coated Optical Fiber Sensor for Detecting VOC Biomarkers of Diabetes.

A non-invasive optical fiber sensor for detecting volatile organic compounds (VOCs) as biomarkers of diabetes is proposed and experimentally demonstrated. It offers a low-cost and straightforward fabrication approach by implementing a one-step spray coating of a ZnO colloidal solution on a glass optical fiber. The structure of the optical fiber sensor is based on a single-mode fiber-coreless silica fiber-single-mode fiber (SMF-CSF-SMF) structure, where the CSF is the sensor region spliced between two SMFs. The ZnO layer of a higher refractive index coated over the sensing region improves the light interaction with the surrounding medium, leading to sensitivity enhancement. The optical properties, morphology, and elemental composition of the ZnO layer were analyzed. The sensing mechanism of the developed sensor is based on a wavelength interrogation technique showing wavelength shifts when the sensor is exposed to various VOC vapor concentration levels. Various concentrations of the three VOCs (including acetone, isopropanol, and ethanol) ranging from 20% to 100% were tested and analyzed. The sensor noticeably shows a significant response towards acetone vapor, with a better sensitivity of 0.162 nm/% vapor than for isopropanol (0.082 nm/% vapor) and ethanol (0.075 nm/% vapor) vapors. The high sensitivity and selectivity towards acetone, a common biomarker for diabetes, offers the potential for further development of this sensor as a smart healthcare system for monitoring diabetic conditions.

Proposal for the detection of breast cancer at its early stage using wave-theory-based analysis in a tapered fiber structure illuminated by the Bessel–Gauss beam for enhanced sensitivity

An analytical exploration of a fiber-optic biosensor with a tapered structure for the detection of breast cancer at its early stage by illuminating the Bessel–Gauss beam in a multilayer structure, using wave-theory-based technique, is proposed to acquire closer results between experimental and theoretical models. By using a Gaussian beam, the observed sensitivity is 2688.5 dB/RIU and 0.204 nm/ng/mL, where all the results are in good agreement with the experimental outcomes reported by Sun et al. [Opt. Commun. 463, 125375 (2020)10.1016/j.optcom.2020.125375]. Thus, this proposed theory is experimentally validated. Now, this tapered theoretical analysis is further extended utilizing the Bessel–Gauss beam, where for the first time, to the best of our knowledge, the discerned sensitivity is enhanced to 14,979.8 dB/RIU and 0.33 nm/ng/mL with a resolution of 6. 68 × 1 0 − 7 , which is 6.59 times superior to the reported results to date. Higher spectral shifts are noticed using the wavelength interrogation technique for the concentration of (2–15) ng/mL of HER2 biological marker. Thus improvement in sensitivity and resolution at lower concentrations is achieved, which indicates the proposed idea for the identification of breast cancer at its early stage.

Validation of Packaged Clad-Etched Fiber Bragg Grating as Underwater Acoustic Sensor

The low intrinsic pressure sensitivity of fiber Bragg grating (FBG) sensors impede their potential applications in the field of hydro-acoustics. This article demonstrates a simple, yet effective way of improving the aggregate hydro-acoustic sensitivity of a bare FBG sensor through clad-etching of the fiber sensor followed by a side-hole polymer packaging. The proposed underwater acoustic sensor system is characterized and validated with a standard lead zirconate titanate (PZT)-based hydrophone under various experimental conditions. This is the first time, to the best of our knowledge, such a high acoustic pressure sensitivity enhancement of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 50$ </tex-math></inline-formula> dB, in comparison with a bare FBG sensor, is reported using a conventional and highly operationally stable wavelength interrogation technique. The minimum detectable acoustic pressure is calculated to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1$ </tex-math></inline-formula> Pa/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(\text {Hz})^{1/2}$ </tex-math></inline-formula> with a maximum responsivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 100$ </tex-math></inline-formula> nm/MPa in the investigated frequency range, with excellent performances in terms of linear response and repeatability. The dynamic range, in the present scenario, is only limited by the range of the interrogation system. The proposed underwater acoustic sensor along with the interrogation technique is a highly compact and cost-effective method for underwater acoustic sensing. Thus, the obtained results can be used for developing and producing long, narrow hydro-acoustic quasi-distributed sensor arrays for marine explorations and other applications.

Wave-theory-based analysis of a fiber optic bio-sensor illuminated by radially polarized Bessel-Gauss beam: an approach for early diagnosis of breast cancer with a high-resolution wavelength-interrogation technique.

With the establishment of validity using authoritative experimental results, an analytical investigation of an SPR-based fiber optic sensor, employing a wave-theory-based technique for determining breast cancer by shining a radially polarized Bessel-Gauss (RPBG) beam, is proposed. First, by using a radially polarized Gaussian (RPG) beam, the observed sensitivity is 9404.61dB/RIU, where the acquired results are in good concurrence with the experimental data reported by Yan etal. [Chin. Opt. Lett.7, 909 (2009)COLHBT1671-7694]. Thus, the proposed theory has been validated with the reported experimental data. This theoretical analysis is further extended by utilizing an RPBG beam, where the observed sensitivity is 21,699.26dB/RIU and 5846nm/RIU, with a resolution of 4.61×10-7, which is 2.5 times superior to the reported results to date. By using an RPBG beam, the proposed method, to our best knowledge, is the first to achieve much higher sensitivity in the area of fiber optic breast cancer detection. The higher sensitivity achieved at lower concentrations of an HER2 biomarker has led to the idea of early diagnosis of breast cancer by optically assessing it at its earlier stage using a high-resolution wavelength-interrogation technique.

Susceptible Plasmonic Photonic Crystal Fiber Sensor with Elliptical Air Holes and External-Flat Gold-Coated Surface

This paper proposes and analyzes a simple surface plasmon resonance (SPR)-based elliptical air hole photonic crystal fiber (PCF) sensor. The fiber structure comprises an analyte channel of the fiber surface coated with a gold layer on the flat surface and the fiber’s external surface. Numerical simulations are conducted using the finite element method (FEM) with an external sensing approach. We found that the thickness of plasmonic material (Au) is the most crucial factor that affects the full width at half maximum (FWHM) and confinement loss amplitude. We also demonstrated that the proposed elliptical air hole SPR-PCF is superior to circular air hole SPR-PCF in terms of confinement loss and FWHM. According to the wavelength interrogation technique, the simulation results show that the designed SPR-PCF sensor can attain a maximum sensitivity of 116,500 nm/RIU and a resolution of 8.58 × 10−7 RIU (RIU: refractive index unit) for the analyte RI of 1.395. We believe the proposed SPR-PCF sensor can be a potential candidate for biomolecular and biological analyte detection.

A High Refractive Index Plasmonic Micro-Channel Sensor Based on Photonic Crystal Fiber.

A new concave shaped high refractive index plasmonic sensor with a micro-channel is proposed in this work, which comprises an analyte channel in the core hole. The sensor is elaborately designed to reduce the interference effect from the metal coating. Furthermore, the impact of the proposed structure on the sensitivity is also investigated by engineering the geometric parameters using the finite element method. We select gold as the plasmonic material in this theoretical study because it is widely used to fabricate plasmonic and metamaterial devices due to its chemical stability and compatibility. According to wavelength interrogation technique, simulations results show that this sensor can obtain maximal wavelength sensitivity of 10,050 nm/refractive index unit. In view of the excellent indicators of this device, it has important development potential in chemical and biological research fields.

Molecularly Imprinted Polymer-Based Optical Sensor for Isopropanol Vapor

Recent advances have allowed the monitoring of several volatile organic compounds (VOCs) in human exhaled breath, and many of them are being utilized as a biomarker to diagnose several diseases, including diabetes. Among several VOCs, isopropanol (IPA) has been reported as a common volatile compound in the exhaled breath of patients with type 1 and type 2 diabetes. In this article, an experimental approach is discussed to develop a highly selective and sensitive IPA vapor sensor system. The fabricated sensor is comprised of a small and portable glass slide coated with molecularly imprinted polymer containing specific binding sites compatible with IPA molecules. The developed sensor is based on the wavelength interrogation technique. The fabricated device is analyzed for the detection of IPA vapor with different concentrations varying from 50% to 100%. The sensor exhibits maximum sensitivities of 0.37, 0.30, and 0.62 nm/%IPA, respectively, for 30, 60, and 90 min, respectively, and an excellent sensitivity of 0.63 nm/%IPA for 120 min exposure along with good selectivity among a similar class of VOCs. The major features of the sensor i.e., small size, portability, cost-effectiveness, high sensitivity, and good selectivity, make it a potential candidate for diabetes monitoring. The promising results of the sensor illustrate its potential in diabetes monitoring applications.

Polarization-Multiplexed Incoherent Broadband Surface Plasmon Resonance: A New Analytical Strategy for Plasmonic Sensing.

Surface plasmon resonance (SPR) is an interfacial phenomenon, and the plasmonic sensors are based on the optical excitation of the collective oscillations of free electrons at a metal-dielectric interface. Here, we present the new development of an incoherent broadband (IBB)-SPR probe combining the wavelength interrogation technique with polarization-multiplexing (PM). The performance characteristics of the so-called PMIBB-SPR strategy was validated for the detection of nonenzymatic aqueous urea samples as a representative example for plasmonic sensing with an excellent wavelength and phase sensitivities of 0.1363 nm/mM and 10.34597 mM/deg, respectively. We further explored the missing link between plasmonic polariton resonance (PPR) and polarization modulation via the measurements of the Stokes parameters of the reflected light. This deepens our understanding of the fundamentals of polarization-multiplexed SPR phenomenon at the interface. This study thus paves the way to develop a new-generation analytical technique with the aim of tracking various real-time chemical and biological molecular interactions occurring at the interfaces.

Design of an ultra-sensitive bimetallic anisotropic PCF SPR biosensor for liquid analytes sensing.

In this research work, an anisotropic photonic crystal fiber (PCF) biosensor working on a refractive index (RI) variation and based on surface plasmon resonance (SPR) is presented. Liquid analytes (LA) having a RI within the range of 1.340 to 1.380 RIU are investigated from the proposed biosensor. Spectroscopy analysis of LA having RI values of 1.340 RIU, 1.360 RIU, and 1.380 RIU is performed from the developed sensing setup for modeling an ultrasensitive biosensor. The numerical analysis of the sensing parameters for the proposed sensor presents a maximum wavelength sensitivity (WS) of 20000 nm/RIU for x- polarization (x - pol.) and 18000 nm/RIU for y- polarization (y - pol.), respectively, using the wavelength interrogation technique. Maximum amplitude sensitivity (AS) of 2158 RIU-1 and 3167 RIU-1 is obtained for x - pol. and y - pol., respectively, using the amplitude interrogation technique. Maximum sensor resolution (SR) of 5.00 × 10-6RIU and 5.55 × 10-6RIU is obtained for x - pol. and y - pol., respectively. The linear relationship of the resonant wavelength (RW) with the RI produces R2 = 0.9972 and R2 = 0.9978, corresponding to a degree (2) for x - pol. and y - pol., respectively. The figure of merit (FOM) for x - pol. and y - pol. are 93.45 RIU-1 and 105.88 RIU-1, respectively. The sensing parameters have obtained the maximum value for the LA having a RI value of 1.375 RIU.

A Voyage from Plasmonic to Hybrid Waveguide Refractive Index Sensors Based on Wavelength Interrogation Technique: a Review

A Voyage from Plasmonic to Hybrid Waveguide Refractive Index Sensors Based on Wavelength Interrogation Technique: a Review

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.

Milled Microchannel-Assisted Open D-Channel Photonic Crystal Fiber Plasmonic Biosensor

A surface plasmon resonance (SPR) based photonic crystal fiber (PCF) sensor having a milled microchannel, and an open D-channel has been proposed in this paper. The sensor shows good functionality in the wide sensing range of 1.14-1.36 Refractive Index Units (RIU) of the analyte, having the capability to detect low refractive index (RI). The Finite Element Method (FEM) based numerical investigations dictate that the proposed sensor has been able to gain a maximum wavelength sensitivity of 53,800 nm/RIU according to the wavelength interrogation technique. The amplitude interrogations show that the sensor has the highest amplitude sensitivity of 328 RIU−1. The highest FOM (Figure of Merit) has been found to be 105 RIU−1. The sensor evinces a minimum wavelength resolution of $1.86\times 10 ^{-6}$ RIU, which secures high detection accuracy. A circular perfectly matched layer (PML) is implemented in the sensor’s outermost layer as a boundary condition to absorb surface radiations. Gold is the plasmonic metal, while TiO2 acts as the adhesive layer for gold attachment on silica. Due to the high sensitivity with a broad range of analyte detection, the sensor is well suited for practical biochemical detection purposes.

Analysis of a Single Solid Core Flat Fiber Plasmonic Refractive Index Sensor

In this article, a single solid core flat fiber (SSCFF) refractive index sensor based on surface plasmon resonance (SPR) is proposed and analyzed numerically using the finite element method (FEM). The proposed flat fiber consists of a single array of five circular holes. Among them the central hole is made of GeO2-doped silica which is forming the core. Other holes are filled with air and situated symmetrically on both sides of the central solid core. The upper flat surface of the fiber is coated with a thin plasmonic gold layer which is protected by an active titanium dioxide layers. Analyte is situated on top of these layers. The wavelength interrogation technique is applied to study the coupling characteristics between the core-guided mode and the surface plasmon mode as well as for the refractive index measurement. Numerical analysis results show that this sensor is able to detect high refractive index analytes from 1.49 to 1.54 with a good linear response. Additionally, the dependence of surface plasmonic resonance wavelength on analyte refractive index is studied. The maximum wavelength sensitivity of this sensor is found to be 4782 nm/RIU with a high resolution of 2.09 × 10−5 RIU. The effects of different structural parameters on loss spectrum are studied in detail to optimize this SSCFF structure. In comparison to traditional PCF, this SSCFF structure is fabrication complexity free as well as a suitable candidate for developing portable devices and high refractive index analyte sensors, particularly chemical and protein sensors.

High sensitivity hollow core circular shaped PCF surface plasmonic biosensor employing silver coat: A numerical design and analysis with external sensing approach

This article numerically offers and analyses a hollow core circular shaped photonic crystal fiber-based surface plasmon resonance (CH-PCF-SPR) biosensor. The biosensor sensitivity is analyzed with applying a mode solver built finite element method (FEM) incorporating multi-physics software “COMSOL”. A nano film of silver is coated as sensing layer on the external surface for easy sensing and more practical realization. The biosensor unveils the highest wavelength sensitivity valued 21000 nm/RIU and amplitude sensitivity valued 2456 RIU−1, and corresponding wavelength resolution of 4.76 × 10−6 RIU and amplitude resolution of 4.07 × 10−6 RIU, respectively, using wavelength interrogation technique (WIT) and technique of amplitude interrogation (AIT), in detecting effective refractive index range 1.33 RIU and 1.42 RIU. Besides, the consequence of changing structural parameters like – pitch, diameter of air hole, various plasmonic metals and silver (Ag) layer thickness are also resulted in results section. The sensitivity of the offered sensor is analyzed to examine the means of spectral loss depth, resolution and amplitude sensitivity. In arrears to the modest scheme, highly sensitive and resolution nature, the offered design can be precisely applied in detection of bio molecular analytes

Broad range and highly sensitive optical pH sensor based on Hierarchical ZnO microflowers over tapered silica fiber

In present work we report the fabrication and characterization of optical fiber pH sensor using smart hydrogel coating over Zinc Oxide (ZnO) microflowers. ZnO microflowers were hydrothermally grown over chemically etched tapered multi-mode fiber (MMF). Mainly, the sensing head contains two layers in which one is ZnO microflower and another is pH sensitive hydrogel layer. The variation in pH of liquid around the sensing probe causes the swelling and shrinkage of hydrogel which leads the change in its refractive index (RI). The work of ZnO microflower is to enhance the evanescent waves that interact with the change in RI of hydrogel which causes the variations of wavelength dips with respect to each pH solutions. The sensitivity was estimated by using wavelength interrogation technique. The ZnO microflower based sensor is highly sensitive for wide range pH values (both high and low range of pH varied from pH = 3 to pH = 7 and pH = 7 to pH = 11, respectively). The sensitivity of ZnO microflower based MMF sensor was found to be 2.59 nm/pH and 0.70 nm/pH for both acidic and basic media, respectively. In addition to high sensitivity, the proposed sensor shows fast response time and good stability and reproducibility.

INVITED] Highly sensitive LSPR based photonic crystal fiber sensor with embodiment of nanospheres in different material domain

We report a highly sensitive Localized surface plasmon resonance (LSPR) based photonic crystal fiber (PCF) sensor by embedding an array of gold nanospheres into the first layer of air-holes of PCF. We present a comprehensive analysis on the basis of progressive variation of refractive indices of analytes as well as sizes of the nanospheres. In the proposed sensing scheme, refractive indices of the analytes have been changed from 1 to 1.41(RIU), accompanied by alteration of the sizes of nanospheres ranging 40–70 nm. The entire study has been executed in the context of different material based PCFs (viz. phosphate and crown) and the corresponding results have been analyzed and compared. We observe a declining trend in modal loss in each set of PCFs with increment of RI of the analyte. Lower loss has been observed in case of crown based PCF. The sensor shows highest sensitivity ∼27,000 nm/RIU for crown based PCF for nanosphere of 70 nm with average wavelength interrogation sensitivity ∼5333.53 nm/RIU. In case of phosphate based PCF, highest sensitivity is found to be ∼18,000 nm/RIU with an average interrogation sensitivity ∼4555.56 nm/RIU for 40 nm of Au nanosphere. Moreover, the additional sensing parameters have been observed to highlight the better design of the modelled LSPR based photonic crystal fiber sensor. As such, the resolution (R), limit of detection (LOD) and sensitivity (S) of the proposed sensor in each case (viz. phosphate and crown PCF) have been discussed by using wavelength interrogation technique. The proposed study provides a basis for detailed investigation of LSPR phenomenon for PCF utilizing noble metal nanospheres (AuNPs).

A wide range and highly sensitive optical fiber pH sensor using polyacrylamide hydrogel

Abstract In the present study we report the fabrication and characterization of no-core fiber sensor (NCFS) using smart hydrogel coating for pH measurement. The no-core fiber (NCF) is stubbed between two single-mode fibers with SMA connector before immobilizing of smart hydrogel. The wavelength interrogation technique is used to calculate the sensitivity of the proposed sensor. The result shows a high sensitivity of 1.94 nm/pH for a wide range of pH values varied from 3 to 10 with a good linear response. In addition to high sensitivity, the fabricated sensor provides a fast response time with a good stability, repeatability and reproducibility.