Reflector-less nanoparticles doped optical fiber biosensor for the detection of proteins: Case thrombin

Comparative study of optical fiber immunosensors based on traditional antibody or nanobody for detecting HER2

In this study, we present a novel biomarker detection platform employing a modified S-tapered fiber coated with gold nanoparticle/graphene oxide (GNP/GO) for quantifying human epidermal growth factor receptor-2 (HER2) concentrations, using antibodies as sensing elements. The fabrication of this device involves implementing an in-situ layer-by-layer technique coupled with a chemical adsorption step to achieve the self-assembly of GNP, GO, and antibodies on the STF surface. The detection mechanism relies on monitoring the refractive index changes induced by the adsorption of HER2 onto the immobilized antibodies. For comparative analysis, both monoclonal antibody (mAb) and the novel nanobody (Nb) were employed in constructing the STF immunosensor, referred to as the mAb immunosensor and Nb immunosensor, respectively. Spectral analysis results highlight that the Nb immunosensor exhibits twice the sensitivity of the mAb immunosensor. This enhanced sensitivity is attributed to the small size, high antigen affinity, strong specificity, and structural stability of Nb. The Nb immunosensor demonstrated an impressive detection limit of 0.001 nM for HER2, surpassing the detection limit of the mAb immunosensor. These findings underscore the potential of the proposed Nb immunosensor as a promising and sensitive tool for HER2 detection, contributing to the diagnosis and prognosis of breast cancer. Furthermore, the simplicity of production and excellent optical performance position the Nb immunosensor as a prospective real-time biosensor with minimal cytotoxicity.

Scattering integral equation formulation for intravascular inclusion biosensing

A dielectric waveguide, inserted into blood vessels, supports its basic mode that is being scattered by a near-field intravascular inclusion. A rigorous integral equation formulation is performed and the electromagnetic response from that inhomogeneity is semi-analytically evaluated. The detectability of the formation, based on spatial distribution of the recorded signal, is estimated by considering various inclusion sizes, locations and textural contrasts. The proposed technique, with its variants and generalizations, provides a generic versatile toolbox to efficiently model biosensor layouts involved in healthcare monitoring and disease screening.

Characterization of optical fibers doped with nanoparticles for distributed displacement sensing

High-scattering optical fibers have emerged as a key component in distributed sensing systems, primarily due to their capacity to enhance signal-to-noise ratio. This paper presents an experimental characterization of optical fibers doped with oxide nanoparticles for displacement sensing. They were manufactured using the phase-separation technique and different doping compounds, including calcium, strontium, lanthanum and magnesium. The Rayleigh backscattering (RBS) signatures in time and frequency domains were acquired using an Optical Backscatter Reflectometer (OBR). The maximum representative length, backscattering gain and strain sensitivity were evaluated. The results indicate that the fiber co-doped with magnesium and erbium chlorides offered the best compromise between strain sensitivity (0.96 pm/μ ϵ) and maximum length (17 m). For conditions of single and multiple perturbations, strain saturation was reached at ≥7000 μm and <1500 μm, respectively. In addition, the results reveal that, under a condition of variable temperature (30-60 °C), the sensor response becomes significantly nonlinear over length, requiring a technique for temperature cross-sensitivity mitigation that accounts for nonlinearities in sensitivity and hysteresis.

All-fiber label-free optical fiber biosensors: from modern technologies to current applications [Invited]

Biosensors are established as promising analytical tools for detecting various analytes important in biomedicine and environmental monitoring. Using fiber optic technology as a sensing element in biosensors offers low cost, high sensitivity, chemical inertness, and immunity to electromagnetic interference. Optical fiber sensors can be used in in vivo applications and multiplexed to detect several targets simultaneously. Certain configurations of optical fiber technology allow the detection of analytes in a label-free manner. This review aims to discuss recent advances in label-free optical fiber biosensors from a technological and application standpoint. First, modern technologies used to build label-free optical fiber-based sensors will be discussed. Then, current applications where these technologies are applied are elucidated. Namely, examples of detecting soluble cancer biomarkers, hormones, viruses, bacteria, and cells are presented.

Humanoid-shaped WaveFlex biosensor for the detection of food contamination

High-toxicity secondary metabolites called aflatoxin are naturally produced by the fungus Aspergillus. In a warm, humid climate, Aspergillus growth can be considerably accelerated. The most dangerous chemical among all aflatoxins is aflatoxin B1 (AFB1), which has the potential to cause cancer and several other health risks. As a result, food forensicists now urgently need a method that is more precise, quick, and practical for aflatoxin testing. The current study focuses on the development of a highly sensitive, specific, label-free, and rapid detection method for AFB1 using a novel humanoid-shaped fiber optic WaveFlex biosensor (refers to a plasmon wave-based fiber biosensor). The fiber probe has been functionalized with nanomaterials (gold nanoparticles, graphene oxide and multiwalled carbon nanotubes) and anti-AFB1 antibodies to enhance the sensitivity and specificity of the developed sensor. The findings demonstrate that the developed sensor exhibits a remarkable low detection limit of 34.5 nM and exceptional specificity towards AFB1. Furthermore, the sensor demonstrated exceptional characteristics such as high stability, selectivity, reproducibility, and reusability. These essential factors highlight the significant potential of the proposed WaveFlex biosensor for the accurate detection of AFB1 in diverse agricultural and food samples.

Recent Advancements of LSPR Fiber-Optic Biosensing: Combination Methods, Structure, and Prospects

Fiber-optic biosensors based on localized surface plasmon resonance (LSPR) have the advantages of great biocompatibility, label-free, strong stability, and real-time monitoring of various analytes. LSPR fiber-optic biosensors have attracted extensive research attention in the fields of environmental science, clinical medicine, disease diagnosis, and food safety. The latest development of LSPR fiber-optic biosensors in recent years has focused on the detection of clinical disease markers and the detection of various toxic substances in the environment and the progress of new sensitization mechanisms in LSPR fiber-optic sensors. Therefore, this paper reviews the LSPR fiber-optic sensors from the aspects of working principle, structure, and application fields in biosensors. According to the structure, the sensor can be divided into three categories: traditional ordinary optical fiber, special shape optical fiber, and specialty optical fiber. The advantages and disadvantages of existing and future LSPR fiber-optic biosensors are discussed in detail. Additionally, the prospect of future development of fiber-optic biosensors based on LSPR is addressed.

Review: 3-Aminopropyltriethoxysilane (APTES) Deposition Methods on Oxide Surfaces in Solution and Vapor Phases for Biosensing Applications

Surface functionalization and bioreceptor immobilization are critical processes in developing a highly sensitive and selective biosensor. The silanization process with 3-aminopropyltriethoxysilane (APTES) on oxide surfaces is frequently used for surface functionalization because of beneficial characteristics such as its bifunctional nature and low cost. Optimizing the deposition process of the APTES layer to obtain a monolayer is crucial to having a stable surface and effectively immobilizing the bioreceptors, which leads to the improved repeatability and sensitivity of the biosensor. This review provides an overview of APTES deposition methods, categorized into the solution-phase and vapor-phase, and a comprehensive summary and guide for creating stable APTES monolayers on oxide surfaces for biosensing applications. A brief explanation of APTES is introduced, and the APTES deposition methods with their pre/post-treatments and characterization results are discussed. Lastly, APTES deposition methods on nanoparticles used for biosensors are briefly described.

2D Temperature Field Reconstruction Using Optical Frequency Domain Reflectometry and Machine-Learning Algorithms

We present experimental results on the reconstruction of the 2D temperature field on the surface of a 250 × 250 mm sensor panel based on the distributed frequency shift measured by an optical backscatter reflectometer. A linear regression and a feed-forward neural network algorithm, trained by varying the temperature field and capturing thermal images of the panel, are used for the reconstruction. In this approach, we do not use any information about the exact trajectory of the fiber, material properties of the sensor panel, and a temperature sensitivity coefficient of the fiber. Mean absolute errors of 0.118 °C and 0.086 °C are achieved in the case of linear regression and feed-forward neural network, respectively.

Cost-Effective Fiber Optic Solutions for Biosensing

In the last years, optical fiber sensors have proven to be a reliable and versatile biosensing tool. Optical fiber biosensors (OFBs) are analytical devices that use optical fibers as transducers, with the advantages of being easily coated and biofunctionalized, allowing the monitorization of all functionalization and detection in real-time, as well as being small in size and geometrically flexible, thus allowing device miniaturization and portability for point-of-care (POC) testing. Knowing the potential of such biosensing tools, this paper reviews the reported OFBs which are, at the moment, the most cost-effective. Different fiber configurations are highlighted, namely, end-face reflected, unclad, D- and U-shaped, tips, ball resonators, tapered, light-diffusing, and specialty fibers. Packaging techniques to enhance OFBs' application in the medical field, namely for implementing in subcutaneous, percutaneous, and endoscopic operations as well as in wearable structures, are presented and discussed. Interrogation approaches of OFBs using smartphones' hardware are a great way to obtain cost-effective sensing approaches. In this review paper, different architectures of such interrogation methods and their respective applications are presented. Finally, the application of OFBs in monitoring three crucial fields of human life and wellbeing are reported: detection of cancer biomarkers, detection of cardiovascular biomarkers, and environmental monitoring.

Aptamer-Based Sensors for Thrombin Detection Application

Thrombin facilitates the aggregation of platelet in hemostatic processes and participates in the regulation of cell signaling. Therefore, the development of thrombin sensors is conducive to comprehending the role of thrombin in the course of a disease. Biosensors based on aptamers screened by SELEX have exhibited superiority for thrombin detection. In this review, we summarized the aptamer-based sensors for thrombin detection which rely on the specific recognitions between thrombin and aptamer. Meanwhile, the unique advantages of different sensors including optical and electrochemical sensors were also highlighted. Especially, these sensors based on electrochemistry have the potential to be miniaturized, and thus have gained comprehensive attention. Furthermore, concerns about aptamer-based sensors for thrombin detection, prospects of the future and promising avenues in this field were also presented.

Refractive Index and Temperature Sensing Performance of Microfiber Modified by UV Glue Distributed Nanoparticles

Dielectric materials with high refractive index have been widely studied to develop novel photonic devices for modulating optical signals. In this paper, the microfibers were modified by silicon nanoparticles (NPs) and silver NPs mixed in UV glue with ultra-low refractive index, respectively, whose corresponding optical and sensing properties have been studied and compared. The influence from either the morphological parameters of microfiber or the concentration of NPs on the refractive index sensing performance of microfiber has been investigated. The refractive index sensitivities for the microfiber tapers elaborated with silver NPs and silicon NPs were experimentally demonstrated to be 1382.3 nm/RIU and 1769.7 nm/RIU, respectively. Furthermore, the proposed microfiber was encapsulated in one cut of capillary to develop a miniature temperature probe, whose sensitivity was determined as 2.08 nm/°C, ranging from 28 °C to 43 °C.

Progress on Optical Fiber Biochemical Sensors Based on Graphene

Graphene, a novel form of the hexagonal honeycomb two-dimensional carbon-based structural material with a zero-band gap and ultra-high specific surface area, has unique optoelectronic capabilities, promising a suitable basis for its application in the field of optical fiber sensing. Graphene optical fiber sensing has also been a hotspot in cross-research in biology, materials, medicine, and micro-nano devices in recent years, owing to prospective benefits, such as high sensitivity, small size, and strong anti-electromagnetic interference capability and so on. Here, the progress of optical fiber biochemical sensors based on graphene is reviewed. The fabrication of graphene materials and the sensing mechanism of the graphene-based optical fiber sensor are described. The typical research works of graphene-based optical fiber biochemical sensor, such as long-period fiber grating, Bragg fiber grating, no-core fiber and photonic crystal fiber are introduced, respectively. Finally, prospects for graphene-based optical fiber biochemical sensing technology will also be covered, which will provide an important reference for the development of graphene-based optical fiber biochemical sensors.

Microfluidic electrochemical magnetoimmunosensor for ultrasensitive detection of interleukin-6 based on hybrid of AuNPs and graphene

Cytokines are important factors in the early diagnosis of autoimmune diseases and require high sensitivity, high selectivity and quantitative detection. We proposed a miniaturized electrochemical magneto-immunosensor (EC-MIS) on portable interleukin-6 (IL-6) detection based on this requirement. Firstly, a micro-fabricated working electrode is electrochemically modified with a hybrid of reduced graphene oxide (rGO) and gold nanoparticles (AuNPs). Increased surface area and enhanced charge transfer rate improve the performance of this immunosensor on sensitivity. Secondly, magnetic beads attached with the capture antibody (cAb) are employed in sandwich immunoassay. This kind of immunoassay is immobilized on the working electrode surface by an external magnet to enrich the analyte IL-6. Thirdly, the last two features are combined and integrated on a microfluidic device in order to restrict the sample at certain areas and ease the operation of detection. With our prototypic EC-MIS operated in amperometric mode, we have achieved the detection of IL-6 with a linear range from 0.97 to 250 pg/mL and a limit of detection (LOD) of 0.42 pg/mL. Real serum samples were demonstrated and compared with benchtop equipment's results.

Perspectives on Assembling Coronavirus Spikes on Fiber Optics to Reveal Broadly Recognizing Antibodies and Generate a Universal Coronavirus Detector

In time of COVID-19 biological detection technologies are of crucial relevance. We propose here the use of state of the art optical fiber biosensors to address two aspects of the fight against SARS-CoV-2 and other pandemic human coronaviruses (HCoVs). Fiber optic biosensors functionalized with HCoV spikes could be used to discover broadly neutralizing antibodies (bnAbs) effective against known HCoVs (SARS-CoV, MERS-CoV and SARS-CoV-2) and likely future ones. In turn, identified bnAbs, once immobilized onto fiber optic biosensors, should be capable to detect HCoVs as diagnostic and environmental sensing devices. The therapeutic and preventative value of bnAbs is immense as they can be used for passive immunization and for the educated development of a universal vaccine (active immunization). Hence, HCoV bnAbs represent an extremely important resource for future preparedness against coronavirus-borne pandemics. Furthermore, the assembly of bnAb-based biosensors constitutes an innovative approach to counteract public health threats, as it bears diagnostic competence additional to environmental detection of a range of pandemic strains. This concept can be extended to different pandemic viruses, as well as bio-warfare threats that entail existing, emerging and extinct viruses (e.g., the smallpox-causing Variola virus). We report here the forefront fiber optic biosensor technology that could be implemented to achieve these aims.

Immunosensing Based on Optical Fiber Technology: Recent Advances

The evolution of optical fiber technology has revolutionized a variety of fields, from optical transmission to environmental monitoring and biomedicine, given their unique properties and versatility. For biosensing purposes, the light guided in the fiber core is exposed to the surrounding media where the analytes of interest are detected by different techniques, according to the optical fiber configuration and biofunctionalization strategy employed. These configurations differ in manufacturing complexity, cost and overall performance. The biofunctionalization strategies can be carried out directly on bare fibers or on coated fibers. The former relies on interactions between the evanescent wave (EW) of the fiber and the analyte of interest, whereas the latter can comprise plasmonic methods such as surface plasmon resonance (SPR) and localized SPR (LSPR), both originating from the interaction between light and metal surface electrons. This review presents the basics of optical fiber immunosensors for a broad audience as well as the more recent research trends on the topic. Several optical fiber configurations used for biosensing applications are highlighted, namely uncladded, U-shape, D-shape, tapered, end-face reflected, fiber gratings and special optical fibers, alongside practical application examples. Furthermore, EW, SPR, LSPR and biofunctionalization strategies, as well as the most recent advances and applications of immunosensors, are also covered. Finally, the main challenges and an outlook over the future direction of the field is presented.