Fiber Optic Surface Plasmon Resonance Research Articles

Innovative FO-SPR Label-free Strategy for Detecting Anti-RBD Antibodies in COVID-19 Patient Serum and Whole Blood.

The ongoing COVID-19 pandemic has emphasized the urgent need for rapid, accurate, and large-scale diagnostic tools. Next to this, the significance of serological tests (i.e., detection of SARS-CoV-2 antibodies) also became apparent for studying patients’ immune status and past viral infection. In this work, we present a novel approach for not only measuring antibody levels but also profiling of binding kinetics of the complete polyclonal antibody response against the receptor binding domain (RBD) of SARS-CoV-2 spike protein, an aspect not possible to achieve with traditional serological tests. This fiber optic surface plasmon resonance (FO-SPR)-based label-free method was successfully accomplished in COVID-19 patient serum and, for the first time, directly in undiluted whole blood, omitting the need for any sample preparation. Notably, this bioassay (1) was on par with FO-SPR sandwich bioassays (traditionally regarded as more sensitive) in distinguishing COVID-19 from control samples, irrespective of the type of sample matrix, and (2) had a significantly shorter time-to-result of only 30 min compared to >1 or 4 h for the FO-SPR sandwich bioassay and the conventional ELISA, respectively. Finally, the label-free approach revealed that no direct correlation was present between antibody levels and their kinetic profiling in different COVID-19 patients, as another evidence to support previous hypothesis that antibody-binding kinetics against the antigen in patient blood might play a role in the COVID-19 severity. Taking all this into account, the presented work positions the FO-SPR technology at the forefront of other COVID-19 serological tests, with a huge potential toward other applications in need for quantification and kinetic profiling of antibodies.

A Study of Improved Bimetallic Graphene–Based Fiber Optic Surface Plasmon Resonance (FOSPR) Biosensor

A Study of Improved Bimetallic Graphene–Based Fiber Optic Surface Plasmon Resonance (FOSPR) Biosensor

Real-Time Thickness Measurement of Marine Oil Spill by Fiber-Optic Surface Plasmon Resonance Sensors

Rapid detection of marine oil spills is becoming increasingly critical in the face of frequent marine oil spills. Oil slick thickness measurement is critical in the hazard assessment of such oil leaks. As surface plasmon resonance (SPR) sensors are sensitive to slight changes in refractive index, they can monitor offshore oil spills arising from significant differences in the refractive index between oil and water. This study presents a gold-film fiber-optic surface plasmon resonance (FOSPR) sensor prepared by polydopamine accelerated wet chemical plating for rapid and real-time measurement of oil slick thickness. We examined oil thickness detection at two interfaces, namely, water-oil and air-oil. Detection sensitivity of −1.373%/mm is obtained at the water-oil interface in the thickness range of 0–5 mm; detection sensitivity of −2.742%/mm is obtained at the air-oil interface in the thickness range of 0–10 mm. Temperature and salinity present negligible effects on the oil slick thickness measurement. The fabricated FOSPR sensor has the ability to detect the presence of oil as well as quantify the oil thickness. It has favorable repeatability and reusability, demonstrating the significant potential for use in the estimation of marine oil slick thickness.

Optical fiber SPR sensor for the detection of fluoride contamination in drinking water

Optical fiber SPR sensor for the detection of fluoride contamination in drinking water

High Figure of Merit SPR Sensor Based on Raspberry-Like Silica

To address the problems that the surface plasmon resonance (SPR) sensor is not sensitive enough to detect biomolecules in the refractive index range (RI=1.33-1.34), and the traditional methods to enhance the sensitivity cause the sensor poor bioaffinity, this paper proposed raspberry-like silica assisted high figure of merit (FOM) fiber-optic SPR sensor. The finite element method results show that when the raspberry-like silica is introduced to the SPR sensor, the resonant electric field intensity on the sensor surface is 2.97 times stronger than that of SPR sensors only. Raspberry-like silica particles composed of different noble metals nanoparticles (AuNPs, PtNPs, and CuNPs) were prepared to compare and analyze the effects of different nanoparticles on the sensing performance. The sensing experiments showed that AuNPs raspberry-like silica had the most excellent performance, enabling the sensor to achieve high sensitivity of 5264.3 nm/RIU, which is 2.65 times higher than the Au film SPR sensor. The fitting calculations showed that the AuNPs raspberry-like silica assisted SPR sensor had a high FOM of 42.9 RIU-1, 1.9 times more than the Au film SPR sensor. In addition, the sensor has good temperature stability, repeatability, and generality after the corresponding test. The proposed raspberry-like structure provides a new approach to obtaining both high sensitivity and high FOM for the SPR sensor, which makes the sensor potential for biosensing.

Numerical Analyses of Liquid-Core Fiber Optic SPR Sensor with Nano-Porous Sio2 as Inner Coating

In this paper, a novel type of liquid-core fiber optic SPR sensor with a nano-porous SiO2 inner coating is proposed. The nano-porous SiO2 is deposited on the inner wall of the quartz tube. Due to the flexible and adjustable refractive index of the deposited material, the RI detection range of the sensor is expanded. The simulation results show that the proposed sensor owns good responses in both low and high refractive index regions, with the corresponding RI sensitivities of 1043.71 nm/RIU and 1234.86 nm/RIU respectively, while the FWHM is only about 20 nm. There are some potential applications for the proposed sensor in environmental monitoring, biochemical detection, food safety etc.

Tapered Optical Fiber Spr Sensor for Salinity Measurement with High Sensitivity

Tapered Optical Fiber Spr Sensor for Salinity Measurement with High Sensitivity

High-Sensitivity Biconical Optical Fiber Spr Salinity Sensor with a Compact Size by Fiber Grinding Technique

High-Sensitivity Biconical Optical Fiber Spr Salinity Sensor with a Compact Size by Fiber Grinding Technique

A study of highly sensitive D-shaped optical fiber surface plasmon resonance based refractive index sensor using grating structures of Ag-TiO2 and Ag-SnO2

In this study, we propose a design and simulation of a highly sensitive surface plasmon resonance (SPR) based single-mode D-shaped optical fiber refractive index sensor in the near-infrared (NIR) region. It consists grating structure of silver coated with titanium dioxide (TiO2) and Tin dioxide (SnO2) layer on the core-cladding interface. With the help of the finite element method (FEM), the proposed optical fiber sensors are optimized with various geometrical parameters. Proposed optimized structures are investigated and various performance parameters are calculated. It is found that performance parameters enhance with TiO2/SnO2 coated on Ag grating structure at a particular thickness of TiO2/SnO2. Due to this more generations of surface plasmons take place on metal-metal oxide structures. We find the maximum sensitivity of 15.31 μm / RIU and 9.81 μm / RIU for Ag-TiO2 and Ag-SnO2 grating structure respectively which shows a better result in comparison to the other reported work. So proposed structure may have great potential to enhance the sensing ability of optical fiber-based sensors as compared to the other conventional SPR based optical fiber sensors.

A Fiber-Optic Surface Plasmon Resonance Sensor for Bio-Detection in Visible to Near-Infrared Images.

In this paper, we demonstrate a fiber-optic surface plasmon resonance (FO-SPR) biosensor based on image processing and back propagation (BP) neural network. The transmitted light of the FO-SPR sensor was captured by using visible (VIS) and near-infrared (NIR) CMOS sensors. The optical information related to the SPR effect was extracted from images based on grayscale conversion and an edge detection algorithm. To achieve accurate monitoring of refractive index (RI) changes, the grayscale means of the VIS and NIR images and the RGB summation of the edge-detected images were used as training and test inputs for the BP neural network. We verified the effectiveness and superiority of this sensing system by experiments on sodium chloride solution identification and protein binding detection. This work is promising for practical applications in standardized biochemical sensing.

High figure of merit fiber optic surface plasmon resonance sensor with topological insulator (BSTS)

High figure of merit fiber optic surface plasmon resonance sensor with topological insulator (BSTS)

Performance improvement approaches for optical fiber SPR sensors and their sensing applications

Optical fiber surface plasmon resonance (SPR) sensors point toward promising application potential in the fields of biomarker detection, food allergen screening, and environmental monitoring due to their unique advantages. This review outlines approaches in improving the fiber SPR sensing performance, e.g., sensitivity, detection accuracy, reliability, cross-sensitivity, selectivity, convenience and efficiency, and corresponding sensing applications. The sensing principles of SPR sensors, especially the performance indicators and their influencing factors, have been introduced. Current technologies for improving the fiber SPR performance and their application scenarios are then reviewed from the aspects of fiber substrate, intrinsic layer (metal layer), and surface nanomaterial modification. Reasonable design of the substrate can strengthen the evanescent electromagnetic field and realize the multi-parameter sensing, and can introduce the in situ sensing self-compensation, which allows corrections for errors induced by temperature fluctuation, non-specific binding, and external disturbances. The change of the intrinsic layer can adjust the column number, the penetration depth, and the propagation distance of surface plasmon polaritons. This can thereby promote the capability of sensors to detect the large-size analytes and can reduce the full width at half-maximum of SPR curves. The modification of various-dimensionality nanomaterials on the sensor surfaces can heighten the overlap integral of the electromagnetic field intensity in the analyte region and can strengthen interactions between plasmons and excitons as well as interactions between analyte molecules and metal surfaces. Moreover, future directions of fiber SPR sensors are prospected based on the important and challenging problems in the development of fiber SPR sensors.

Highly sensitive fiber-optic SPR sensor with surface coated TiO2/MWCNT composite film for hydrogen sulfide gas detection

Hydrogen sulfide (H2S) gas has a severe effect on the respiratory system of the human body and ambient environment, necessitating development of on-line H2S gas sensors with high performance for safety and health concerns. Here, we proposed a fiber-optic surface plasmon resonance sensor for H2S detection employing TiO2 nanoparticles and multilayer carbon nanotubes composite (TiO2/MWCNT) as sensing film, featuring desirable advantages of high sensitivity, selectivity, and real-time detection. Benefiting from special structure and large specific surface area of MWCNTs, the adsorption capacity of sensing surface to gas molecules can be significantly enhanced. Moreover, the high carrier mobility of MWCNTs can further promote the charge transfer between TiO2 and H2S. These unique features of TiO2/MWCNT composite film result in an obvious improvement of sensitivity for H2S detection. Experimental results show that the maximum sensitivity of 21.76 pm ppm−1 (picometer/part-per-million) and detection limit of 0.2 ppm can be obtained by appropriately optimizing the componential constitutions of TiO2/MWCNT composite. Such detection limit is strikingly lower than the threshold concentrations in workplace set by Federal Institute for Occupational Safety (10 ppm). In addition, the favorable selectivity, response/recovery times, repeatability and stability were demonstrated as well. This facile and cost-effective work provides a novel strategy for constructing high performance H2S gas sensor with fast response and real-time detection, which has prospective application in the fields of human health and environmental conservation.

Construction of an enzyme-based all-fiber SPR biosensor for detection of enantiomers

Chiral analysis of amino acids (AAs) is of great importance in medical science due to the distinctive effect of AA isomers on human health. Although various chiral recognition techniques have been developed, the quantitative chiral recognition of low-level AA isomers remains challenging. Here, we combined the fiber optic SPR with an enzyme-substrate recognition mechanism to construct a direct-assay-type chiral AA biosensor. As a proof-of-concept attempt, a recently discovered Rasamsonia emersonii D-amino acid oxidase (ReDAAO) with a wide substrate spectrum and high stability was immobilized on the graphene oxide and gold nanorods composites (GO-AuNRs), using both EDC/NHS coupling and the gold-binding peptide (GBP) method. Such a biosensor can distinguish two AA isomers at the same concentration. It achieved specific detection of D-amino acids (D-AAs) with a linear range from 5x10-4 mM to 30 mM. Furthermore, it showed good resistance to enantiomeric interference. When the percentage of D-AA increases in the isomer mixture, a good linear relationship between the D/(D + L)-AA ratio and SPR spectral shift was obtained. This unique combination of the enzyme, nanocomposite, and SPR taps into the rich reservoir of proteins for chiral receptors. It lays the foundation for protein-based chiral recognition of other clinically important small molecules in future biosensor designs.

A plug-and-play optical fiber SPR sensor for simultaneous measurement of glucose and cholesterol concentrations

A plug-and-play surface plasmon resonance (SPR) dual-parameter optical fiber biosensor is reported, in which Au film was firstly coated on the fiber surface for exciting SPR and the end half of the Au film was modified with Au nanoparticles to generate double SPR resonance valleys. For simultaneous detecting of glucose and cholesterol concentrations, modified P-mercaptophenylboronic acid (PMBA) and β-cyclodextrin (β-CD) were subsequently coated on the surface of sensor probe. Due to the cis-diol structure of glucose, it can interact with PMBA, leading to a red shift of one SPR resonant valley, whose maximum wavelength shift is 11.228 nm in the range of 0–1.7 mM glucose concentration. On the same time, the cholesterol molecules can realize the host-guest combination with β-CD, leading to a red shift of another SPR resonant valley, and the maximum wavelength shift is 18.893 nm in the cholesterol concentration range of 0–300 nM. The detection limits of the sensor to glucose and cholesterol are 0.00078 mM and 0.012 nM, respectively. The enhances the practical value of the dual-parameter sensor. Both theory and experiment results verify the feasibility of the “plug-and-play” sensor to measure the dual biomass of glucose and cholesterol with ultra-low detection limit and good selectivity. The proposed method provides a huge research value for the optical fiber sensor in multi-parameter measurement.

Detection limit enhancement of fiber optic localized surface plasmon resonance biosensor by increased scattering efficiency and reduced background signal

To reduce the limit of detection (LOD) in fiber optic localized surface plasmon resonance (FO LSPR) sensors, design strategies with high scattering efficiency and low background signal are proposed. Despite the cost effectiveness of fabrication, miniaturization capabilities, and high portability of optic fibers, the LOD is a limiting factor for fiber optic sensor applications. To overcome this limitation, we propose methods to increase the scattering efficiency and reduce background signal using gold capping and reactive-ion etching (RIE). Specifically, three strategies are implemented. First, the effective coverage for detection is selected by analyzing the sensor output according to the density of gold nanoparticles (AuNPs), which have been immobilized on the cross-section of the optical fiber. Next, the sensitivity is studied by examining changes in scattering efficiency of the AuNPs grown with different capping times. Third, RIE is performed on the fiber optic surface to reduce the reflectance in areas where the AuNPs are not fixed, thereby decreasing the background signal. Thyroglobulin, amyloid beta monomer, and oligomer are measured using the thus-fabricated FO LSPR sensor. The results are compared with those obtained with a sensor fabricated without using these strategies. The former showed the lower LOD and higher accuracy for biomarkers of the two. • The effective coverage of AuNPs is selected on the optical fiber. • For improvement of scattering efficiency, AuNPs are directly grown on fiber optic surface. • Surface etching is executed for reduction of background in bare surface. • The enhancement of the LODs is evaluated for several biomarkers.

2D material assisted SMF-MCF-MMF-SMF based LSPR sensor for creatinine detection.

The purpose of this work is to propose a simple, portable, and sensitive biosensor structure based on singlemode fiber-multicore fiber-multimode fiber-singlemode fiber (SMF-MCF-MMF-SMF) for the detection of creatinine in the human body. Chemical etching has been used to modify the diameter of the sensing probe to approximately 90 μm in order to generate strong evanescent waves (EWs). The sensor probe is functionalized with graphene oxide (GO), gold nanoparticles (AuNPs), molybdenum disulfide nanoparticles (MoS2-NPs), and creatininase (CA) enzyme. The concentration of creatinine is determined using fiber optic localized surface plasmon resonance (LSPR). While EWs are used to enhance the LSPR effect of AuNPs, two-dimensional (2D) materials (GO and MoS2-NPs) are used to increase biocompatibility, and CA is used to increase probe specificity. Additionally, HR-TEM and UV-visible spectroscopy are used to characterize and measure the nanoparticle (NP) morphology and absorption spectrum, respectively. SEM is used to characterize the NPs immobilized on the surface of the fiber probe. The sensor probe's reusability, reproducibility, stability, selectivity, and pH test results are also tested to verify the sensor performance. The sensitivity of proposed sensor is 0.0025 nm/μM, has a standard deviation of 0.107, and has a limit of detection of 128.4 μM over a linear detection range of 0 - 2000 μM.

2D Materials-Based Fiber Optic SPR Biosensor for Cancer Detection at 1550 nm

Two-dimensional (2D) materials-based fiber-optic surface plasmon resonance (SPR) sensor is proposed to diagnose the different cancers at the wavelength of 1550 nm. In this work, five types of cancerous cell lines such as Jurkat, HeLa, PC12, MDA-MB-231, MCF7, and normal cell lines are considered for analysis. The power loss through proposed SPR sensor is maximum at a specific angle <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\theta }_{\textit {SPR}}$ </tex-math></inline-formula> . Resonance angle <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\theta }_{\textit {SPR}}$ </tex-math></inline-formula> shift to another angle for different cancerous cell lines. The angular shift and power loss of different cancerous cells are different from their normal cells due to the different refractive indices (RIs) of each cell. The proposed work is helpful in the detection of different types of cancer such as blood, cervical, Adrenal Glands and Breast Cancer by measuring the angular shift in peak power loss. For angular power loss calculations, transfer matrix method (TMM) is used. The sensor structure consists of fiber core, clad, metal layer, and 2D material layer. In 2D material, role of MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and graphene are investigated on the performance of sensor. Further, three structures such as (i) probe 1: SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -perfluorinated (PF)-Ag (ii) probe 2: SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -PF-Ag-MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , and (iii) probe 3: SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -PF-Ag-graphene are designed and investigated in detail. Calculated values of a figure of merit (FOM) for probe 2, probe 1, and probe 3 sensor structure are 6654.54 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , 4645.21 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , and 832.88 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , respectively. Sensitivity and limit of detection (LoD) are also calculated from power loss spectrum. Probe 2 provides maximum FOM in all and exhibits three times larger FOM than earlier reported cancer cell sensors. The calculated LoD in case of probe 2 for Jurkat, HeLa, PC12, MDA-MB-231, MCF7 are 0.4550 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> , 0.4510 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> , 0.4440 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> , 0.4350 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> and 0.430 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> respectively with maximum sensitivity of 232.33 deg./RIU. Thus, LoD of the proposed sensor is quite low that makes it better than most of the recently reported SPR based fiber-optic sensors. The proposed fiber optic SPR sensor with high FOM and low LoD is a suitable candidate for the early diagnosis of different types of cancers.

Fiber-optic meta-tip with multi-sensitivity resonance dips for humidity sensing

In response to the requirements of small effective sensing volume for simultaneous interpreting of resonant peaks with different sensing sensitivities, a surface plasmon resonance (SPR) fiber-optic probe based on non-uniform Au groove array is proposed, which realizes relative humidity (RH) sensing by coating silk fibroin film. The RH meta-tip is mainly composed of multi-mode fiber (MMF), a metasurface, and silk fibroin film. The metasurface is transferred to the end face of the MMF by the “contact and separate” transfer method, and then a layer of silk fibroin is coated on the metasurface by dipping method. Because of the interaction of interference and plasma excitation, the proposed SPR probe has many resonance dips with different refractive index (RI) sensitivities, which has the potential to monitor multiple sensing parameters. Because the RI of the silk fibroin film is directly affected by the external environment RH, the phase matching conditions of the propagating surface plasmon polaritons (SPPs) change accordingly, leading to the shifts in the resonance wavelength of those dips. By further improving the functional integration of the fiber-optic SPR probe, the single-ended sensor paves the way for chemical and biological sensing.

Portable fiber-optic SPR platform for the detection of NS1-antigen for dengue diagnosis

Here, we present a portable, selective and cost-effective fiber-optic surface plasmon resonance (SPR) based platform for early detection of Dengue virus. NS1 protein was targeted as the biomarker of dengue. Antibody-antigen specific binding was exploited for NS1 antigen detection. The binding of antibody was assisted by a self-assembled monolayer of alkanethiols on the surface of silver-coated unclad fiber. A wavelength interrogation mode of SPR was utilized to detect NS1 antigen in the dynamic range of 0.2–2.0 μg/ml. The 40 nm thick silver coated optical fiber exhibited resonance wavelength around 500 nm and change in resonance wavelength was monitored for each attachment step on the fiber. The sensitivity at the lowest concentration of NS1 antigen was found to be 54.7 nm/(μg/ml). The limit of detection of the sensor was found to be 0.06 μg/ml, which lies in the physiological range of NS1 protein present in the infected blood, hence the present technique may provide a very early detection advantage. Real blood serum samples were also successfully tested on the set-up, confirming compatibility with the conventional methods. The presented field-deployable platform has wide applications in mass monitoring of dengue, such as during outbreaks and epidemics.