Long period fiber grating nano-optrode for cancer biomarker detection

Optical fiber biosensors toward in vivo detection

This review takes stock of the various optical fiber-based biosensors that could be used for in vivo applications. We discuss the characteristics that biosensors must have to be suitable for such applications and the corresponding transduction modes. In particular, we focus on optical fiber biosensors based on fluorescence, evanescent wave, plasmonics, interferometry, and Raman phenomenon. The operational principles, implemented solutions, and performances are described and debated. The different sensing configurations, such as the side- and tip-based fiber biosensors, are illustrated, and their adaptation for in vivo measurements is discussed. The required implementation of multiplexed biosensing on optical fibers is shown. In particular, the use of multi-fiber assemblies, one of the most optimal configurations for multiplexed detection, is discussed. Different possibilities for multiple localized functionalizations on optical fibers are presented. A final section is devoted to the practical in vivo use of fiber-based biosensors, covering regulatory, sterilization, and packaging aspects. Finally, the trends and required improvements in this promising and emerging field are analyzed and discussed.

Magnetic microspheres enhanced peanut structure cascaded lasso shaped fiber laser biosensor for cancer marker-CEACAM5 detection in serum

The detection of trace cancer markers in body fluids such as blood/serum is crucial for cancer diseases screening and treatment, which requires high sensitivity and specificity of biosensors. In this study, a peanut structure cascaded lasso (PSCL) shaped fiber sensing probe based on fiber laser demodulation method was proposed to specifically detect the carcinoembryonic antigen related cell adhesion molecules 5 (CEACAM5) protein in serum. Thanks for the narrow linewidth and high signal-to-noise ratio (SNR) of the laser spectrum, it is easier to distinguish small spectral changes than interference spectrum. Adding the antibody modified magnetic microspheres (MMS) to form the sandwich structure of "antibody-antigen-antibody-MMS", and amplified the response caused by biomolecular binding. The limit of detection (LOD) for CEACAM5 in buffer could reach 0.11 ng/mL. Considering the common threshold of 5 ng/mL for CEA during medical screening and the cut off limit of 2.5 ng/mL for some kits, the LOD of proposed biosensor meets the actual needs. Human serum samples from a hospital were used to validate the real sensing capability of proposed biosensor. The deviation between the measured value in various serum samples and the clinical value ranged from 1.9 to 9.8 %. This sensing scheme holds great potential to serve as a point of care testing (POCT) device and extend to more biosensing applications.

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.

Label-Free Biochemical Sensing Using Processed Optical Fiber Interferometry: A Review

Over the last 20 years, optical fiber-based devices have been exploited extensively in the field of biochemical sensing, with applications in many specific areas such as the food processing industry, environmental monitoring, health diagnosis, bioengineering, disease diagnosis, and the drug industry due to their compact, label-free, and highly sensitive detection. The selective and accurate detection of biochemicals is an essential part of biosensing devices, which is to be done through effective functionalization of highly specific recognition agents, such as enzymes, DNA, receptors, etc., over the transducing surface. Among many optical fiber-based sensing technologies, optical fiber interferometry-based biosensors are one of the broadly used methods with the advantages of biocompatibility, compact size, high sensitivity, high-resolution sensing, lower detection limits, operating wavelength tunability, etc. This Review provides a comprehensive review of the fundamentals as well as the current advances in developing optical fiber interferometry-based biochemical sensors. In the beginning, a generic biosensor and its several components are introduced, followed by the fundamentals and state-of-art technology behind developing a variety of interferometry-based fiber optic sensors. These include the Mach-Zehnder interferometer, the Michelson interferometer, the Fabry-Perot interferometer, the Sagnac interferometer, and biolayer interferometry (BLI). Further, several technical reports are comprehensively reviewed and compared in a tabulated form for better comparison along with their advantages and disadvantages. Further, the limitations and possible solutions for these sensors are discussed to transform these in-lab devices into commercial industry applications. At the end, in conclusion, comments on the prospects of field development toward the commercialization of sensor technology are also provided. The Review targets a broad range of audiences including beginners and also motivates the experts helping to solve the real issues for developing an industry-oriented sensing device.

Fiber Laser-Based Lasso-Shaped Biosensor for High Precision Detection of Cancer Biomarker-CEACAM5 in Serum

Detection of trace tumor markers in blood/serum is essential for the early screening and prognosis of cancer diseases, which requires high sensitivity and specificity of the assays and biosensors. A variety of label-free optical fiber-based biosensors has been developed and yielded great opportunities for Point-of-Care Testing (POCT) of cancer biomarkers. The fiber biosensor, however, suffers from a compromise between the responsivity and stability of the sensing signal, which would deteriorate the sensing performance. In addition, the sophistication of sensor preparation hinders the reproduction and scale-up fabrication. To address these issues, in this study, a straightforward lasso-shaped fiber laser biosensor was proposed for the specific determination of carcinoembryonic antigen (CEA)-related cell adhesion molecules 5 (CEACAM5) protein in serum. Due to the ultra-narrow linewidth of the laser, a very small variation of lasing signal caused by biomolecular bonding can be clearly distinguished via high-resolution spectral analysis. The limit of detection (LOD) of the proposed biosensor could reach 9.6 ng/mL according to the buffer test. The sensing capability was further validated by a human serum-based cancer diagnosis trial, enabling great potential for clinical use. The high reproduction of fabrication allowed the mass production of the sensor and extended its utility to a broader biosensing field.

SERS assisted sandwich immunoassay platforms for ultrasensitive and selective detection of human Thyroglobulin

We developed an immunoassay platform for the detection of human Thyroglobulin (Tg) to be integrated with fine-needle aspiration biopsy for early detection of lymph node metastases in thyroid cancer patients. The sensing platform detects Tg by a sandwich immunoassay involving a self-assembled surface-enhanced Raman scattering (SERS) substrate assisted by functionalized gold nanoparticles that provide additional Raman signal amplification and improved molecular specificity. Specifically, the SERS-active substrates were functionalized with Tg Capture antibodies and fabricated either on-chip or on optical fiber tips by nanosphere lithography. Gold nanoparticles were functionalized with Detection antibodies and conjugated with 4-mercaptobenzoic acid, which serves as a Raman reporter. The sandwich assay platform was validated in the planar configuration and a detection limit as low as 7 pg/mL was successfully achieved. Careful morphological examination of the SERS substrates before and after Tg measurements further assessed the effective capture of nanoparticles and correlated the average nanoparticle coverage with the Tg concentration obtained by SERS measurements. The sandwich assay was successfully demonstrated on washout fluids of fine needle aspiration biopsies from cancer patients and confirmed the high specificity of the proposed methodology when complex biological matrices are considered. Finally, SERS optrodes were fabricated and successfully used to detect Tg concentration by applying the same bio-recognition strategy and Raman interrogation through an optical fiber. This opens the possibility of transferring the Tg detection approach to the optical fiber tip to develop point-of-care platforms that can be directly integrated into fine needle aspiration biopsies.

Microfluidic immunosensor based on a graphene oxide functionalized double helix microfiber coupler for anti-Müllerian hormone detection

A label-free microfluidic immunosensor based on the double helix microfiber coupler (DHMC) coated with graphene oxide (GO) was proposed for the specific detection of anti-Müllerian hormone (AMH). Two single-mode optical fibers were twisted in a parallel direction, the coning machine was used to fuse and taper them, and the high-sensitivity DHMC was obtained. To make a stable sensing environment, it was immobilized in a microfluidic chip. And then, the DHMC was modified by GO and bio-functionalized by the AMH monoclonal antibodies (anti-AMH MAbs) for the specific detection of AMH. The experimental results showed that the detection range of the immunosensor for AMH antigen solutions was 200 fg/mL∼50 µg/mL, the detection of limit (LOD) was ∼235.15 fg/mL, and the detection sensitivity and the dissociation coefficient were ∼3.518 nm/(log(mg/mL)) and ∼1.85 × 10 ^{- 12} M, respectively. The alpha fetoprotein (AFP), des-carboxy prothrombin (DCP), growth stimulation expressed gene 2 (ST2) and AMH serum were used to confirm the excellent specific and clinical properties of the immunosensor, showing that the proposed immunosensor was easy-made and can be potentially applied in the biosensing field.

Innovative Photonic Sensors for Safety and Security, Part III: Environment, Agriculture and Soil Monitoring

In order to complete this set of three companion papers, in this last, we focus our attention on environmental monitoring by taking advantage of photonic technologies. After reporting on some configurations useful for high precision agriculture, we explore the problems connected with soil water content measurement and landslide early warning. Then, we concentrate on a new generation of seismic sensors useful in both terrestrial and under water contests. Finally, we discuss a number of optical fiber sensors for use in radiation environments.

Innovative Photonic Sensors for Safety and Security, Part I: Fundamentals, Infrastructural and Ground Transportations

Our group, involving researchers from different universities in Campania, Italy, has been working for the last twenty years in the field of photonic sensors for safety and security in healthcare, industrial and environment applications. This is the first in a series of three companion papers. In this paper, we introduce the main concepts of the technologies employed for the realization of our photonic sensors. Then, we review our main results concerning the innovative applications for infrastructural and transportation monitoring.

Innovative Photonic Sensors for Safety and Security, Part II: Aerospace and Submarine Applications

The employability of photonics technology in the modern era's highly demanding and sophisticated domain of aerospace and submarines has been an appealing challenge for the scientific communities. In this paper, we review our main results achieved so far on the use of optical fiber sensors for safety and security in innovative aerospace and submarine applications. In particular, recent results of in-field applications of optical fiber sensors in aircraft monitoring, from a weight and balance analysis to vehicle Structural Health Monitoring (SHM) and Landing Gear (LG) monitoring, are presented and discussed. Moreover, underwater fiber-optic hydrophones are presented from the design to marine application.

Ultrasensitive Optical Fiber Sensors Working at Dispersion Turning Point: Review

Optical fiber sensors working at the dispersion turning point (DTP) have served as promising candidates for various sensing applications due to their ultrahigh sensitivity. In this review, recently developed ultrasensitive fiber sensors at the DTP, including fiber couplers, fiber gratings, and interferometers, are comprehensively analyzed. These three schemes are outlined in terms of operation principles, device structures, and sensing applications. We focus on sensitivity enhancement and optical transducers, we evaluate each sensing scheme based on the DTP principle, and we discuss relevant challenges, aiming to provide some clues for future research.

Black Phosphorous Aptamer-based Platform for Biomarker Detection

Black phosphorus nanostructures (nano-BPs) mainly include BP nanosheets (BP NSs), BP quantum dots (BPQDs), and other nano-BPs-based particles at nanoscale. Firstly discovered in 2014, nano-BPs are one of the most popular nanomaterials. Different synthesis methods are discussed in short to understand the basic concepts and developments in synthesis. Exfoliated nano-BPs, i.e. nano-BPs possess high surface area, high photothermal conversion efficacy, excellent biocompatibility, high charge carrier mobility (~1000 cm^-2V^-1s^-1), thermal conductivity of 86 Wm^-1K^-1; and these properties make it a highly potential candidate for fabrication of biosensing platform. These properties enable nano-BPs to be promising photothermal/drug delivery agents as well as in electrochemical data storage devices and sensing devices; and in super capacitors, photodetectors, photovoltaics and solar cells, LEDs, super-conductors, etc. Early diagnosis is very critical in the health sector scenarios. This review attempts to highlight the attempts made towards attaining stable BP, BP-aptamer conjugates for successful biosensing applications. BP-aptamer- based platforms are reviewed to highlight the significance of BP in detecting biological and physiological markers of cardiovascular diseases and cancer; to be useful in disease diagnosis and management.

Advanced Lab-on-Fiber Optrodes Assisted by Oriented Antibody Immobilization Strategy

Lab-on-fiber (LoF) optrodes offer several advantages over conventional techniques for point-of-care platforms aimed at real-time and label-free detection of clinically relevant biomarkers. Moreover, the easy integration of LoF platforms in medical needles, catheters, and nano endoscopes offer unique potentials for in vivo biopsies and tumor microenvironment assessment. The main barrier to translating the vision close to reality is the need to further lower the final limit of detection of developed optrodes. For immune-biosensing purposes, the assay sensitivity significantly relies on the capability to correctly immobilize the capture antibody in terms of uniform coverage and correct orientation of the bioreceptor, especially when very low detection limits are requested as in the case of cancer diagnostics. Here, we investigated the possibility to improve the immobilization strategies through the use of hinge carbohydrates by involving homemade antibodies that demonstrated a significantly improved recognition of the antigen with ultra-low detection limits. In order to create an effective pipeline for the improvement of biofunctionalization protocols to be used in connection with LoF platforms, we first optimized the protocol using a microfluidic surface plasmon resonance (mSPR) device and then transferred the optimized strategy onto LoF platforms selected for the final validation. Here, we selected two different LoF platforms: a biolayer interferometry (BLI)-based device (commercially available) and a homemade advanced LoF biosensor based on optical fiber meta-tips (OFMTs). As a clinically relevant scenario, here we focused our attention on a promising serological biomarker, Cripto-1, for its ability to promote tumorigenesis in breast and liver cancer. Currently, Cripto-1 detection relies on laborious and time-consuming immunoassays. The reported results demonstrated that the proposed approach based on oriented antibody immobilization was able to significantly improve Cripto-1 detection with a 10-fold enhancement versus the random approach. More interestingly, by using the oriented antibody immobilization strategy, the OFMTs-based platform was able to reveal Cripto-1 at a concentration of 0.05 nM, exhibiting detection capabilities much higher (by a factor of 250) than those provided by the commercial LoF platform based on BLI and similar to the ones shown by the commercial and well-established bench-top mSPR Biacore 8K system. Therefore, our work opened new avenues into the development of high-sensitivity LoF biosensors for the detection of clinically relevant biomarkers in the sub-ng/mL range.

Ultrasound waves in tumors via needle irradiation for precise medicine

Grounded in the interdisciplinary crosstalk among physics and biological sciences, precision medicine-based diagnosis and treatment strategies have recently gained great attention for the actual applicability of new engineered approaches in many medical fields, particularly in oncology. Within this framework, the use of ultrasounds employed to attack cancer cells in tumors to induce possible mechanical damage at different scales has received growing attention from scholars and scientists worldwide. With these considerations in mind, on the basis of ad hoc elastodynamic solutions and numerical simulations, we propose a pilot study for in silico modeling of the propagation of ultrasound waves inside tissues, with the aim of selecting proper frequencies and powers to be irradiated locally through a new teragnostic platform based on Lab-on-Fiber technology, baptized as a hospital in the needle and already the object of a patent. It is felt that the outcomes and the related biophysical insights gained from the analyses could pave the way for envisaging new integrated diagnostic and therapeutic approaches that might play a central role in future applications of precise medicine, starting from the growing synergy among physics, engineering and biology.

Label-free detection of breast cancer cells using a functionalized tilted fiber grating

The detection of circulating tumor cells (CTCs) still faces a huge challenge partially because of low abundance of CTCs (1-10 cells/mL). In this work, a plasmonic titled fiber Bragg grating biosensor is proposed for detection of breast cancer cells. The biosensor is made by an 18° TFBG with a 50 nm-thick gold nanofilm coating over the surface of the fiber, further immobilized with a specific antibody against GPR30, which is a membrane receptor expressed in many breast cancers, serving as bait. In vitro tests have confirmed that the proposed biosensor can detect breast cancer cells in concentration of 5 cells/mL within 20 minutes and has good linearity in the range of 5-1000 cells/mL, which has met the requirement of CTC detection in real conditions. Furthermore, theoretical analysis based on the experimental results shows that the limit of detection can even reach single-cell level. Our proposed biosensor has a simple structure, is easy to manufacture, is of small size, and has a good performance, making it a good choice for real-time, label-free, and milliliter-volume detection of cancer cells in future.

Optical Fiber-Integrated Metasurfaces: An Emerging Platform for Multiple Optical Applications

The advent of metasurface technology has revolutionized the field of optics and photonics in recent years due to its capability of engineering optical wavefronts with well-patterned nanostructures at subwavelength scale. Meanwhile, inspired and benefited from the tremendous success of the “lab-on-fiber” concept, the integration of metasurface with optical fibers has drawn particular interest in the last decade, which establishes a novel technological platform towards the development of “all-in-fiber” metasurface-based devices. Thereby, this review aims to present and summarize the optical fiber-integrated metasurfaces with the current state of the art. The application scenarios of the optical fiber metasurface-based devices are well classified and discussed accordingly, with a brief explanation of physical fundamentals and design methods. The key fabrication methods corresponding to various optical fiber metasurfaces are summarized and compared. Furthermore, the challenges and potential future research directions of optical fiber metasurfaces are addressed to further leverage the flexibility and versatility of meta-fiber-based devices. It is believed that the optical fiber metasurfaces, as a novel all-around technological platform, will be exploited for a large range of applications in telecommunication, sensing, imaging, and biomedicine.

Recent advancements in optical biosensors for cancer detection

Optical biosensors are rapid, real-time, and portable, have a low detection limit and a high sensitivity, and have a great potential for diagnosing various types of cancer. Optical biosensors can detect cancer in a few million malignant cells, in comparison to conventional diagnosis techniques that use 1 billion cells in tumor tissue with a diameter of 7 nm-10 nm. Current cancer detection methods are also costly, inconvenient, complex, time consuming, and require technical specialists. This review focuses on recent advances in optical biosensors for early detection of cancer. It is primarily concerned with advancements in the design of various biosensors using resonance, scattering, chemiluminescence, luminescence, interference, fluorescence, absorbance or reflectance, and various fiber types. The development of various two-dimensional materials with optical properties such as biocompatibility, field enhancement, and a higher surface-to-volume ratio, as well as advancements in microfabrication technologies, have accelerated the development of optical sensors for early detection of cancer and other diseases. Surface enhanced Raman spectroscopy technology has the potential to detect a single molecule with high specificity, and terahertz waves are a recently explored technology for cancer detection. Due to the low electromagnetic interference, small size, multiplexing, and remote sensing capabilities of optical fiber-based platforms, they may be a driving force behind the rapid development of biosensors. The advantages and disadvantages of existing and future optical biosensor designs for cancer detection are discussed in detail. Additionally, a prospect for future advancements in the development of optical biosensors for point-of-care and clinical applications is highlighted.

Feasibility analysis of an ultrasound on line diagnostic approach for oral and bone surgery

During implant surgery procedures, surgical precision is an essential prerequisite for the functional and aesthetic success of the prosthetic crown to be placed on the dental implant. A modern implant surgical approach should be standardized as much as possible to guarantee extreme precision in the insertion of the implant into the upper and lower bone jaws. Among the most common surgical errors during implant surgery there is the over-preparation of the surgical alveolus with possible damage to the contiguous anatomical structures. To avoid this problem, in the recent years, there has been an increasing attention to the development of new control techniques. In this paper, we describe an innovative ultrasound approach, which exploits the integration of an electro-acoustic transducer with the surgical drill used for realizing the alveolus in the bone that will host the implant. Specifically, he proposed approach is based on the "time-of-flight" detection technique for measuring the thickness of the residual bone subjected to the drilling. In order to demonstrate the feasibility of the proposed approach, here we report on a detailed numerical analysis aimed at studying the propagation of ultrasonic waves through the drill-bit and through the involved tissues. The obtained results confirm the validity of our approach, and enable for a future first prototype implementation of a hi-tech surgical drill-bit, which in general is suitable not only for dental implant surgery but also for other uses in oral surgery, maxillofacial surgery and for bone surgery.

Design and validation of fiber optic localized surface plasmon resonance sensor for thyroglobulin immunoassay with high sensitivity and rapid detection

A simple optical fiber sensor based on localized surface plasmon resonance was constructed for direct and rapid measurement of thyroglobulin (Tg). Specific tests for Tg in patients that have undergone thyroidectomy are limited because of insufficient sensitivity, complicated procedures, and in some cases, a long time to yield a result. A sensitive, fast, and simple method is necessary to relieve the psychological and physical burden of the patient. Various concentrations of Tg were measured in a microfluidic channel using an optical fiber sensor with gold nanoparticles. The sensor chip has a detection limit of 93.11 fg/mL with no specificity for other antigens. The potential applicability of the Tg sensing system was evaluated using arbitrary samples containing specific concentrations of Tg. Finally, the sensor can be employed to detect Tg in the patient’s serum, with a good correlation when compared with the commercial kit.

Highly sensitive electrochemical immunosensor using a protein-polyvinylidene fluoride nanocomposite for human thyroglobulin

The highly sensitive detection of serum thyroglobulin (Tg) is essential in the post-treatment follow-up of patients with differentiated thyroid cancer undergoing total or partial thyroidectomy and radioactive iodine ablation and requires sensitive, accurate and stable methods. This work proposes an electrochemical immunosensor for the detection of serum Tg antigen, making use of innovative nanocomposites including polyvinylidene fluoride (PVDF) microparticles coated with streptavidin (MP) and gold nanoparticles (AuNPs). The functionalized polymer matrices were characterized by UV-Vis, FTIR, XPS, SEM, dynamic light scattering, and free surface energy. Immobilization of biotin-labeled anti-thyroglobulin monoclonal antibodies was achieved by binding these to the polymer nanocomposite via streptavidin proteins. The analytical response was measured in quintuplicate and had a linear profile from 2.0 to 10.0 ng/mL Tg, with r² of 0.985. The limits of detection and quantification were excellent, equal to 0.015 and 0.047 ng/mL, respectively. In addition, the recovery factor was equal to 95.4% (1.0 ng/mL Tg). Overall, the innovative polymer-based nanocomposite used herein enabled the production of an electrochemical-based immunosensor with excellent sensitivity, selectivity, and reproducibility. It evidenced the remarkable potential of determining low levels of Tg in in vitro assays, thereby suggesting that it may be considered for the analyzes of serum patients.

Highly sensitive detection of malignant glioma cells using metamaterial-inspired THz biosensor based on electromagnetically induced transparency

Metamaterial-inspired biosensors have been extensively studied recently years for fast and low-cost THz detection. However, only the variation of the resonance frequency has been closely concerned in such sensors so far, whiles the magnitude variation, which also provide important information of the analyte, has not been sufficiently analyzed. In this paper, by the observation of two degree of variations, we propose a label-free biosensing approach for molecular classification of glioma cells. The metamaterial biosensor consisting of cut wires and split ring resonators are proposed to realize polarization-independent electromagnetic induced transparency (EIT) at THz frequencies. Simulated results show that the EIT-like resonance experiences both resonance frequency and magnitude variations when the properties of analyte change, which is further explained with coupled oscillators model theory. The theoretical sensitivity of the biosensor is evaluated up to 496.01 GHz/RIU. In experiments, two types of glioma cells (mutant and wild-type) are cultured on the biosensor surface. The dependences of frequency shifts and the peak magnitude variations on the cells concentrations for different types give new perspective for molecular classification of glioma cells. The measured results indicate that the mutant and wild-type glioma cells can be distinguished directly by observing both the variations of EIT resonance frequency and magnitude at any cells concentrations without antibody introduction. Our metamaterial-based biosensor shows a great potential in the recognition of molecule types of glioma cells, opening alternative way to sensitive biosensing technology.

Long period grating in double cladding fiber coated with graphene oxide as high-performance optical platform for biosensing

In this work, the development and testing of a novel fiber-optic based label-free biosensor is presented, whose performance were verified through the detection of C-reactive protein (CRP) in serum. The device is based on a long period grating fabricated in a double cladding fiber with a W-shaped refractive index (RI) profile. As a result, the working point of the device was tuned to the mode transition region by chemical etching of the outer fiber cladding, obtaining a significant enhancement of the RI sensitivity and an excellent visibility of the grating resonances due to the mode transition in an all-silica structure. The fiber transducer was coated with a nanometric thin layer of graphene oxide in order to provide functional groups for the covalent immobilization of the biological recognition element. A very low limit of detection of about 0.15 ng/mL was obtained during the detection of CRP in serum, and a large working range (1 ng/mL - 100 μg/mL) of clinical relevance has been also achieved.

Magnetic mesoporous CoFe2O4 labels reacted with TMB for use in a sandwiched photothermal immunoassay for thyroglobulin

An innovative photothermal immunoassay with a sandwich-type immunoreaction mode was designed for the sensitive screening of thyroglobulin on capture antibody-coated microtiter plates using a handheld digital thermometer as the readout device.

Selection and characterization of an ssDNA aptamer against thyroglobulin

Thyroglobulin (Tg) is a significant biomarker for the diagnose and postoperative monitoring of differentiated thyroid cancer, and its recognition is urgent due to the rising prevalence. In this study, an ssDNA aptamer against Tg was obtained by capillary electrophoresis-systematic evolution of ligands via exponential enrichment (CE-SELEX). Under the optimized conditions, the sub-library was enriched well through two selection rounds. After high-throughput sequencing, eight candidate sequences were picked out and their affinities towards Tg were observed not in accordance with the order of their frequencies, whereas sequence homology played a significant role in binding affinity. The high-affinity sequence Seq.T-2 with a dissociation constant (K_d) of 3.18 μM was finally selected as the aptamer, and its affinity was confirmed qualitatively by gold nanoparticles colorimetric and quantitatively by thin film interferometry (K_d, 4.51 nM). Besides, molecular docking and dynamics simulation were performed for their binding sites prediction and affinity confirmation. Furthermore, the aptamer was applied for Tg detection, which delivered a detection limit of 5.0 nM as well as with good selectivity, and showed a good linear relationship within a wide range of 10 nM-6.4 μM of Tg spiked into the serum matrix. This study first reported Tg's aptamer which also exhibited the potential in real applications.

Label-Free and Reproducible Chemical Sensor Using the Vertical-Fluid-Array Induced Optical Fiber Long Period Grating (VIOLIN)

Fiber optical refractometers have gained a substantial reputation in biological and chemical sensing domain regarding their label-free and remote-operation working mode. However, the practical breakthrough of the fiber optical bio/chemosensor is impeded by a lack of reconfigurability as well as the explicitness of the determination between bulk and surface refractive indices. In this letter, we further implement the highly flexible and reproducible long period grating called "VIOLIN" in chemical sensing area for the demonstration of moving those obstacles. In this configuration, the liquid is not only leveraged as the chemical carrier but also the periodic modulation of the optical fiber to facilitate the resonant signal. The thiol compound that is adsorbed by the fluidic substrate can be transduced to the pure alteration of the bulk refractive index of the liquid, which can be sensitively perceived by the resonant drift. Taking advantage of its freely dismantled feature, the VIOLIN sensor enables flexible reproduction and high throughput detection, yielding a new vision to the fiber optic biochemical sensing field.

Development of an optical microfiber immunosensor for prostate specific antigen analysis using a high-order-diffraction long period grating

Fiber-optic biosensors are of great interest to many bio/chemical sensing applications. In this study, we demonstrate a high-order-diffraction long period grating (HOD-LPG) for the detection of prostate specific antigen (PSA). A HOD-LPG with a period number of less than ten and an elongated grating pitch could realize a temperature-insensitive and bending-independent biosensor. The bio-functionalized HOD-LPG was capable of detecting PSA in phosphate buffered saline with concentrations ranging from 5 to 500 ng/ml and exhibited excellent specificity. A limit of detection of 9.9 ng/ml was achieved, which is promising for analysis of the prostate specific antigen.

Analysis of uncoated LPGs written in B-Ge doped fiber under proton irradiation for sensing applications at CERN

In this contribution, a complete dissertation concerning the behavior of a Long Period Grating (LPG) inscribed in a B-Ge co-doped optical fiber by means of an excimer laser and exposed to proton irradiation during a recent extensive campaign performed at the European Organization for Nuclear Research (CERN) with a fluence of 4.4·10¹⁵ p∙cm⁻² is provided. The experimental results have been thus combined for the first time to the best of our knowledge with numerical simulations in order to estimate the variations of the major parameters affecting the grating response during the ultra-high dose proton exposure. From the correlation between experimental and numerical analysis, the irradiation exposure was found to induce a maximal variation of the core effective refractive index of ~1.61·10⁻⁴, responsible of a resonance wavelength red shift of ~44 nm in correspondence of the highest absorbed radiation dose of 1.16 MGy. At the same time, a relevant decrease close to ~0.93·10⁻⁴ in the refractive index modulation pertaining to the grating was estimated, leading to a reduction of the resonant dip visibility of ~12 dB. The effect of the proton beam on the spectral response of the LPG device and on the optical fiber parameters was assessed during the relaxation phases, showing a partial recovery only of the wavelength shift without any relevant change in the dip visibility revealing thus a partial recovery only in the refractive index of the core while the reduction of the refractive index modulation observed during the irradiation remained unchanged.

Ultrasensitive tantalum oxide nano-coated long-period gratings for detection of various biological targets

In this work we discussed a label-free biosensing application of long-period gratings (LPGs) optimized in refractive index (RI) sensitivity by deposition of thin tantalum oxide (TaO_x) overlays. Comparing to other thin film and materials already applied for maximizing the RI sensitivity, TaO_x offers good chemical and mechanical stability during its surface functionalization and other biosensing experiments. It was shown theoretically and experimentally that when RI of the overlay is as high as 2 in IR spectral range, for obtaining LPGs ultrasensitive to RI, the overlay's thickness must be determined with subnanometer precision. In this experiment the TaO_x overlays were deposited using Atomic Layer Deposition method that allowed for achieving overlays with exceptionally well-defined thickness and optical properties. The TaO_x nano-coated LPGs show RI sensitivity determined for a single resonance exceeding 11,500 nm/RIU in RI range n_D= 1.335-1.345 RIU, as expected for label-free biosensing applications. Capability for detection of various in size biological targets, i.e., proteins (avidin) and bacteria (Escherichia coli), with TaO_x-coated LPGs was verified using biotin and bacteriophage adhesin as recognition elements, respectively. It has been shown that functionalization process, as well as type of recognition elements and target analyte must be taken into consideration when the LPG sensitivity is optimized. In this work optimized approach made possible detection of small in size biological targets such as proteins with sensitivity reaching 10.21 nm/log(ng/ml).

Immunosensing platform with large detection range using an excessively tilted fiber grating coated with graphene oxide

We report an immunosensing platform with a large detection range using an excessively tilted fiber grating (ExTFG) coated with graphene oxide (GO). ExTFG was inscribed in standard single-mode fiber; GO film was coated on the fiber surface through hydrogen bond. The effectiveness and uniformity of GO deposited on the ExTFG surface were investigated by field emission scanning electron microscopy and energy spectrum method. Bovine serum albumin (BSA) monoclonal antibodies (MAbs) were used as biometric units to link the GO film through a covalent bond for the specific detection of BSA, so as to evaluate the performances of the proposed biosensor. The whole dynamic immobilization process of BSA MAbs and BSA detection were observed by the spectral evolution of the sensor. Experimental results show that the fabricated GO-coated ExTFG biosensor has a large detection range from 1.5 nM-75 nM and fast response for BSA antigen; the limit of detection is ∼0.88  nM by using an optical spectrum analyzer with a resolution of 0.03 nm, and the dissociation constant K_D and the affinity constant K_A are calculated to be ∼6.66×10^-9  M and ∼1.5×10⁸  M^-1, respectively. The proposed GO-coated ExTFG immunosensing platform could lay a foundation for the specific detection of other biomolecules.

Femtomolar Detection by Nanocoated Fiber Label-Free Biosensors

The advent of optical fiber-based biosensors combined with that of nanotechnologies has provided an opportunity for developing in situ, portable, lightweight, versatile, and high-performance optical sensing platforms. We report on the generation of lossy mode resonances by the deposition of nanometer-thick metal oxide films on optical fibers, which makes it possible to measure precisely and accurately the changes in optical properties of the fiber-surrounding medium with very high sensitivity compared to other technology platforms, such as long period gratings or surface plasmon resonances, the gold standard in label-free and real-time biomolecular interaction analysis. This property, combined with the application of specialty structures such as D-shaped fibers, permits enhancing the light-matter interaction. SEM and TEM imaging together with X-EDS tool have been utilized to characterize the two films used, i.e., indium tin oxide and tin dioxide. Moreover, the experimental transmission spectra obtained after the deposition of the nanocoatings have been numerically corroborated by means of wave propagation methods. With the use of a conventional wavelength interrogation system and ad hoc developed microfluidics, the shift of the lossy mode resonance can be reliably recorded in response to very low analyte concentrations. Repeated experiments confirm a big leap in performance thanks to the capability to detect femtomolar concentrations in human serum, improving the detection limit by 3 orders of magnitude when compared with other fiber-based configurations. The biosensor has been regenerated several times by injecting sodium dodecyl sulfate, which proves the capability of sensor to be reused.

Liquefied Petroleum Gas Monitoring System Based on Polystyrene Coated Long Period Grating

In this work, we report the in-field demonstration of a liquefied petroleum gas monitoring system based on optical fiber technology. Long-period grating coated with a thin layer of atactic polystyrene (aPS) was employed as a gas sensor, and an array comprising two different fiber Bragg gratings was set for the monitoring of environmental conditions such as temperature and humidity. A custom package was developed for the sensors, ensuring their suitable installation and operation in harsh conditions. The developed system was installed in a real railway location scenario (i.e., a southern Italian operative railway tunnel), and tests were performed to validate the system performances in operational mode. Daytime normal working operations of the railway line and controlled gas expositions, at very low concentrations, were the searched realistic conditions for an out-of-lab validation of the developed system. Encouraging results were obtained with a precise indication of the gas concentration and external conditioning of the sensor.

Arc-Induced Long Period Gratings from Standard to Polarization-Maintaining and Photonic Crystal Fibers

In this work, we report about our recent results concerning the fabrication of Long Period Grating (LPG) sensors in several optical fibers, through the Electric Arc Discharge (EAD) technique. In particular, the following silica fibers with both different dopants and geometrical structures are considered: standard Ge-doped, photosensitive B/Ge codoped, P-doped, pure-silica core with F-doped cladding, Panda type Polarization-maintaining, and Hollow core Photonic crystal fiber. An adaptive platform was developed and the appropriate “recipe” was identified for each fiber, in terms of both arc discharge parameters and setup arrangement, for manufacturing LPGs with strong and narrow attenuation bands, low insertion losses, and short length. As the fabricated devices have appealing features from the application point of view, the sensitivity characteristics towards changes in different external perturbations (i.e., surrounding refractive index, temperature, and strain) are investigated and compared, highlighting the effects of different fiber composition and structure.

Nano-functionalized long-period fiber grating probe for disease-specific protein detection

Label-free nano-functionalized LPFG based real-time, reusable sensor for sensitive detection of disease-specific proteins.

Plasmonic Optical Fiber-Grating Immunosensing: A Review

Plasmonic immunosensors are usually made of a noble metal (in the form of a film or nanoparticles) on which bioreceptors are grafted to sense analytes based on the antibody/antigen or other affinity mechanism. Optical fiber configurations are a miniaturized counterpart to the bulky Kretschmann prism and allow easy light injection and remote operation. To excite a surface plasmon (SP), the core-guided light is locally outcoupled. Unclad optical fibers were the first configurations reported to this end. Among the different architectures able to bring light in contact with the surrounding medium, a great quantity of research is today being conducted on metal-coated fiber gratings photo-imprinted in the fiber core, as they provide modal features that enable SP generation at any wavelength, especially in the telecommunication window. They are perfectly suited for use with cost-effective high-resolution interrogators, allowing both a high sensitivity and a low limit of detection to be reached in immunosensing. This paper will review recent progress made in this field with different kinds of gratings: uniform, tilted and eccentric short-period gratings as well as long-period fiber gratings. Practical cases will be reported, showing that such sensors can be used in very small volumes of analytes and even possibly applied to in vivo diagnosis.

Label-free fiber optic optrode for the detection of class C β-lactamases expressed by drug resistant bacteria

This paper reports the experimental assessment of an automated optical assay based on label free optical fiber optrodes for the fast detection of class C β-lactamases (AmpC BLs), actually considered as one of the most important sources of resistance to β-lactams antibiotics expressed by resistant bacteria. Reflection-type long period fiber gratings (RT-LPG) have been used as highly sensitive label free optrodes, while a higher affine boronic acid-based ligand was here selected to enhance the overall assay performances compared to those obtained in our first demonstration. In order to prove the feasibility analysis towards a fully automated optical assay, an engineered system was developed to simultaneously manipulate and interrogate multiple fiber optic optrodes in the different phases of the assay. The automated system tested in AmpC solutions at increasing concentrations demonstrated a limit of detection (LOD) of 6 nM, three times better when compared with the results obtained in our previous work. Moreover, the real effectiveness of the proposed optical assay has been also confirmed in complex matrices as the case of lysates of Escherichia coli overexpressing AmpC.

Optimization in nanocoated D-shaped optical fiber sensors

Nanocoated D-shaped optical fibers have been proven as effective sensors. Here, we show that the full width at half minimum (FWHM) of lossy mode resonance can be reduced by optimizing the nanocoating width, thickness and refractive index. As a counterpart, several resonances are observed in the optical spectrum for specific conditions. These resonances are caused by multiple modes guided in the nanocoating. By optimizing the width of the coating and the imaginary part of its refractive index, it is possible to isolate one of these resonances, which allows one to reduce the full width at half minimum of the device and, hence, to increase the figure of merit. Moreover, it is even possible to avoid the need of a polarizer by designing a device where the resonance bands for TE and TM polarization are centered at the same wavelength. This is interesting for the development of optical filters and sensors with a high figure of merit.

Human heart failure biomarker immunosensor based on excessively tilted fiber gratings

A label-free immunosensor platform based on excessively tilted fiber gratings (Ex-TFGs) was developed for highly specific and fast detection of human N-terminal pro-B-type natriuretic peptide (NT-proBNP), which is considered a powerful biomarker for prognosis and risk stratification of heart failure (HF). High-purity anti-NT-proBNP monoclonal antibodies (MAbs) prepared in our laboratory were immobilized on fiber surface through the staphylococcal protein A (SPA) method for subsequent specific binding of the targeted NT-proBNP. Utilizing fiber optic grating demodulation system (FOGDS), immunoassays were carried out in vitro by monitoring the resonance wavelength shift of Ex-TFG biosensor with immobilized anti-NT-proBNP MAbs. Lowest detectable concentration of ~0.5ng/mL for NT-proBNP was obtained, and average sensitivity for NT-proBNP at a concentration range of 0~1.0 ng/mL was approximately 45.967 pm/(ng/mL). Several human serum samples were assessed by the proposed Ex-TFG biomarker sensor, with high specificity for NT-proBNP, indicating potential application in early diagnosing patients with acute HF symptoms.

Enzyme Biosensors for Biomedical Applications: Strategies for Safeguarding Analytical Performances in Biological Fluids

Enzyme-based chemical biosensors are based on biological recognition. In order to operate, the enzymes must be available to catalyze a specific biochemical reaction and be stable under the normal operating conditions of the biosensor. Design of biosensors is based on knowledge about the target analyte, as well as the complexity of the matrix in which the analyte has to be quantified. This article reviews the problems resulting from the interaction of enzyme-based amperometric biosensors with complex biological matrices containing the target analyte(s). One of the most challenging disadvantages of amperometric enzyme-based biosensor detection is signal reduction from fouling agents and interference from chemicals present in the sample matrix. This article, therefore, investigates the principles of functioning of enzymatic biosensors, their analytical performance over time and the strategies used to optimize their performance. Moreover, the composition of biological fluids as a function of their interaction with biosensing will be presented.