Fiber-Optic Chemical Sensors and Fiber-Optic Bio-Sensors

Dual-Lifetime Referencing (t-DLR) Optical Fiber Fluorescent pH Sensor for Microenvironments

The pH behavior in the μm to cm thick diffusion boundary layer (DBL) surrounding many aquatic species is dependent on light-controlled metabolic activities. This DBL microenvironment exhibits different pH behavior to bulk seawater, which can reduce the exposure of calcifying species to ocean acidification conditions. A low-cost time-domain dual-lifetime referencing (t-DLR) interrogation system and an optical fiber fluorescent pH sensor were developed for pH measurements in the DBL interface. The pH sensor utilized dual-layer sol-gel coatings of pH-sensitive iminocoumarin and pH-insensitive Ru(dpp)3-PAN. The sensor has a dynamic range of 7.41 (±0.20) to 9.42 ± 0.23 pH units (95% CI, T = 20 °C, S = 35), a response time (t90) of 29 to 100 s, and minimal salinity dependency. The pH sensor has a precision of approximately 0.02 pHT units, which meets the Global Ocean Acidification Observing Network (GOA-ON) "weather" measurement quality guideline. The suitability of the t-DLR optical fiber pH sensor was demonstrated through real-time measurements in the DBL of green seaweed Ulva sp. This research highlights the practicability of optical fiber pH sensors by demonstrating real-time pH measurements of metabolic-induced pH changes.

Biomarkers and optical based biosensors in cardiac disease detection: early and accurate diagnosis

Rapid and precise detection methods for the early-stage detection of cardiovascular irregularities are crucial to stopping and reducing their development. Cardiovascular diseases (CVDs) are the leading cause of death in the world. Hence, cardiac-related biomarkers are essential for monitoring and managing of process. The necessity for biomarker detection has significantly widened the field of biosensor development. Bio-sensing methods offer rapid detection, low cost, sensitivity, portability, and selectivity in the development of devices for biomarker detection. For the prediction of cardiovascular diseases, some biomarkers can be used, like C-reactive protein (CRP), troponin I or T, creatine kinase (CK-MB), B-type natriuretic peptide (BNP), myoglobin (Mb), suppression of tumorigenicity 2 protein (ST2) and galectin-3 (Gal3). In this review, recent research studies were covered for gaining insight into utilizing optical-based biosensors, including surface plasmon resonance (SPR), photonic crystals (PCs), fluorescence-based techniques, fiber optics, and also Raman spectroscopy biosensors for the ultrasensitive detection of cardiac biomarkers. The main goal of this review is to focus on the improvement of optical biosensors in the future for the diagnosis of heart diseases and to discuss how to enhance their properties for use in medicine. Some main data from each study reviewed are emphasized, including the CVD biomarkers and the response range of the optical-based devices and biosensors.

All-Silicon Photoelectric Biosensor on Chip Based on Silicon Nitride Waveguide with Low Loss

Compared to the widely used compound semiconductor photoelectric sensors, all-silicon photoelectric sensors have the advantage of easy mass production because they are compatible with the complementary metal-oxide-semiconductor (CMOS) fabrication technique. In this paper, we propose an all-silicon photoelectric biosensor with a simple process and that is integrated, miniature, and with low loss. This biosensor is based on monolithic integration technology, and its light source is a PN junction cascaded polysilicon nanostructure. The detection device utilizes a simple refractive index sensing method. According to our simulation, when the refractive index of the detected material is more than 1.52, evanescent wave intensity decreases with the growth of the refractive index. Thus, refractive index sensing can be achieved. Moreover, it was also shown that, compared to a slab waveguide, the embedded waveguide designed in this paper has a lower loss. With these features, our all-silicon photoelectric biosensor (ASPB) demonstrates its potential in the application of handheld biosensors.

The Challenges of O2 Detection in Biological Fluids: Classical Methods and Translation to Clinical Applications

Dissolved oxygen (DO) is deeply involved in preserving the life of cellular tissues and human beings due to its key role in cellular metabolism: its alterations may reflect important pathophysiological conditions. DO levels are measured to identify pathological conditions, explain pathophysiological mechanisms, and monitor the efficacy of therapeutic approaches. This is particularly relevant when the measurements are performed in vivo but also in contexts where a variety of biological and synthetic media are used, such as ex vivo organ perfusion. A reliable measurement of medium oxygenation ensures a high-quality process. It is crucial to provide a high-accuracy, real-time method for DO quantification, which could be robust towards different medium compositions and temperatures. In fact, biological fluids and synthetic clinical fluids represent a challenging environment where DO interacts with various compounds and can change continuously and dynamically, and further precaution is needed to obtain reliable results. This study aims to present and discuss the main oxygen detection and quantification methods, focusing on the technical needs for their translation to clinical practice. Firstly, we resumed all the main methodologies and advancements concerning dissolved oxygen determination. After identifying the main groups of all the available techniques for DO sensing based on their mechanisms and applicability, we focused on transferring the most promising approaches to a clinical in vivo/ex vivo setting.

Environmental Monitoring: A Comprehensive Review on Optical Waveguide and Fiber-Based Sensors

Globally, there is active development of photonic sensors incorporating multidisciplinary research. The ultimate objective is to develop small, low-cost, sensitive, selective, quick, durable, remote-controllable sensors that are resistant to electromagnetic interference. Different photonic sensor designs and advances in photonic frameworks have shown the possibility to realize these capabilities. In this review paper, the latest developments in the field of optical waveguide and fiber-based sensors which can serve for environmental monitoring are discussed. Several important topics such as toxic gas, water quality, indoor environment, and natural disaster monitoring are reviewed.

An Optical Fiber Sensor for Uranium Detection in Water

An optical sensor for uranyl has been prepared based on a gold-plated D-shaped plastic optical fiber (POF) combined with a receptor consisting of a bifunctional synthetic molecule, 11-mercaptoundecylphosphonic acid (MUPA), with a phosphonic group for complexing the considered ion, and a sulfide moiety through which the molecule is fixed at the gold resonant surface as a molecular layer in an easy and reproducible way. The sensor is characterized by evaluating the response in function of the uranyl concentration in aqueous solutions of different compositions and real-life samples, such as tap water and seawater. The mechanism of the uranyl/MUPA interaction was investigated. Two different kinds of interactions of uranyl with the MUPA layer on gold from water are observed: a strong one and a weak one. In the presence of competing metal ions as Ca²⁺ and Mg²⁺, only the strong interaction takes place, with a high affinity constant (around 10⁷ M⁻¹), while a somewhat lower constant (i.e., around 10⁶ M⁻¹) is obtained in the presence of Mg²⁺ which forms stronger complexes with MUPA than Ca²⁺. Due to the high affinity and the good selectivity of the recognition element MUPA, a detection limit of a few μg L⁻¹ is reached directly in natural water samples without any time-consuming sample pretreatment, making it possible for rapid, in situ controls of uranyl by the proposed sensor.

Optical Fiber Probe Microcantilever Sensor Based on Fabry–Perot Interferometer

Optical fiber Fabry–Perot sensors have long been the focus of researchers in sensing applications because of their unique advantages, including highly effective, simple light path, low cost, compact size, and easy fabrication. Microcantilever-based devices have been extensively explored in chemical and biological fields while the interrogation methods are still a challenge. The optical fiber probe microcantilever sensor is constructed with a microcantilever beam on an optical fiber, which opens the door for highly sensitive, as well as convenient readout. In this review, we summarize a wide variety of optical fiber probe microcantilever sensors based on Fabry–Perot interferometer. The operation principle of the optical fiber probe microcantilever sensor is introduced. The fabrication methods, materials, and sensing applications of an optical fiber probe microcantilever sensor with different structures are discussed in detail. The performances of different kinds of fiber probe microcantilever sensors are compared. We also prospect the possible development direction of optical fiber microcantilever sensors.

Design of 3D-Printed Electronic Fiber Optic Sensor to Detect Rhodamine B Reagent: An Initiation to Potential Virus Detection

A fluorescence device based on ultraviolet light is proposed in this paper, which currently stands at the design stage with the eventual aim to potentially detect virus/antibody fluorescence reactions. The designed device is proposed to have the characteristics of high reflectivity, low power consumption, wide spectrum of light source, and proper silver coating. For fabrication and raising product quality, 3D printing technology and a sputtering test will be used. In this connection, this paper firstly introduces the design sources; then, the ideas of inventing fluorescence detection devices based on ultraviolet light, followed by the data analysis as well as discussing the results of computer simulations. The design process, materials, methods, and experiments are demonstrated following the reality work procedure. Instead of directly using a virus or antibodies for the experiment, at the current design stage, we focus on using this device to detect the rhodamine B reagent. Experiment shows that this reagent can be successfully detected. With this achievement, we logically believe that such type of an ultraviolet optical sensor, with further development and testing, may have the possible value to detect a single virus such as COVID-19, as well as other viruses or small molecules. Though there is long way to go to achieve such a goal, future works experimenting with the detection device on real virus or antibodies can take place more efficiently with a good foundation.

A method for the controllable fabrication of optical fiber-based localized surface plasmon resonance sensors

Optical fiber-based Localized Surface Plasmon Resonance (OF-LSPR) biosensors have emerged as an ultra-sensitive miniaturized tool for a great variety of applications. Their fabrication by the chemical immobilization of gold nanoparticles (AuNPs) on the optic fiber end face is a simple and versatile method. However, it can render poor reproducibility given the number of parameters that influence the binding of the AuNPs. In order to develop a method to obtain OF-LSPR sensors with high reproducibility, we studied the effect that factors such as temperature, AuNPs concentration, fiber core size and time of immersion had on the number and aggregation of AuNPs on the surface of the fibers and their resonance signal. Our method consisted in controlling the deposition of a determined AuNPs density on the tip of the fiber by measuring its LSPR signal (or plasmonic signal, Sp) in real-time. Sensors created thus were used to measure changes in the refractive index of their surroundings and the results showed that, as the number of AuNPs on the probes increased, the changes in the Sp maximum values were ever lower but the wavelength shifts were higher. These results highlighted the relevance of controlling the relationship between the sensor composition and its performance.

Transducer Technologies for Biosensors and Their Wearable Applications

The development of new biosensor technologies and their active use as wearable devices have offered mobility and flexibility to conventional western medicine and personal fitness tracking. In the development of biosensors, transducers stand out as the main elements converting the signals sourced from a biological event into a detectable output. Combined with the suitable bio-receptors and the miniaturization of readout electronics, the functionality and design of the transducers play a key role in the construction of wearable devices for personal health control. Ever-growing research and industrial interest in new transducer technologies for point-of-care (POC) and wearable bio-detection have gained tremendous acceleration by the pandemic-induced digital health transformation. In this article, we provide a comprehensive review of transducers for biosensors and their wearable applications that empower users for the active tracking of biomarkers and personal health parameters.

Sensors for Volatile Organic Compounds

This paper provides an overview of recent developments in the field of volatile organic compound (VOC) sensors, which are finding uses in healthcare, safety, environmental monitoring, food and agriculture, oil industry, and other fields. It starts by briefly explaining the basics of VOC sensing and reviewing the currently available and quickly progressing VOC sensing approaches. It then discusses the main trends in materials' design with special attention to nanostructuring and nanohybridization. Emerging sensing materials and strategies are highlighted and their involvement in the different types of sensing technologies is discussed, including optical, electrical, and gravimetric sensors. The review also provides detailed discussions about the main limitations of the field and offers potential solutions. The status of the field and suggestions of promising directions for future development are summarized.

Comprehensive review of conventional and state-of-the-art detection methods of Cryptosporidium

Cryptosporidium is a critical waterborne protozoan pathogen found in water resources that have been a major cause of death and serious illnesses worldwide, costing millions of dollars annually for its detection and treatment. Over the past several decades, substantial efforts have been made towards developing techniques for the detection of Cryptosporidium. Early diagnostic techniques were established based on the existing tools in laboratories, such as microscopes. Advancements in fluorescence microscopy, immunological, and molecular techniques have led to the development of several kits for the detection of Cryptosporidium spp. However, these methods have several limitations, such as long processing times, large sample volumes, the requirement for bulky and expensive laboratory tools, and the high cost of reagents. There is an urgent need to improve these existing techniques and develop low-cost, portable and rapid detection tools for applications in the water quality industry. In this review, we compare recent advances in nanotechnology, biosensing and microfluidics that have facilitated the development of sophisticated tools for the detection of Cryptosporidium spp.Finally, we highlight the advantages and disadvantages, of these state-of-the-art detection methods compared to current analytical methodologies and discuss the need for future developments to improve such methods for detecting Cryptosporidium in the water supply chain to enable real-time and on-site monitoring in water resources and remote areas.

Advanced Optical Sensing of Phenolic Compounds for Environmental Applications

Phenolic compounds are particularly dangerous due to their ability to remain in the environment for a long period of time and their toxic effects. They enter in the environment in different ways, such as waste from paper manufacturing, agriculture (pesticides, insecticides, herbicides), pharmaceuticals, the petrochemical industry, and coal processing. Conventional methods for phenolic compounds detection present some disadvantages, such as cumbersome sample preparation, complex and time-consuming procedures, and need of expensive equipment. Therefore, there is a very large interest in developing sensors and new sensing schemes for fast and easy-to-use methods for detecting and monitoring the phenolic compound concentration in the environment, with special attention to water. Good analytical properties, reliability, and adaptability are required for the developed sensors. The present paper aims at revising the most generally used optical methods for designing and fabricating biosensors and sensors for phenolic compounds. Some selected examples of the most interesting applications of these techniques are also proposed.

Optical Biosensors for Diagnostics of Infectious Viral Disease: A Recent Update

The design and development of biosensors, analytical devices used to detect various analytes in different matrices, has emerged. Biosensors indicate a biorecognition element with a physicochemical analyzer or detector, i.e., a transducer. In the present scenario, various types of biosensors have been deployed in healthcare and clinical research, for instance, biosensors for blood glucose monitoring. Pathogenic microbes are contributing mediators of numerous infectious diseases that are becoming extremely serious worldwide. The recent outbreak of COVID-19 is one of the most recent examples of such communal and deadly diseases. In efforts to work towards the efficacious treatment of pathogenic viral contagions, a fast and precise detection method is of the utmost importance in biomedical and healthcare sectors for early diagnostics and timely countermeasures. Among various available sensor systems, optical biosensors offer easy-to-use, fast, portable, handy, multiplexed, direct, real-time, and inexpensive diagnosis with the added advantages of specificity and sensitivity. Many progressive concepts and extremely multidisciplinary approaches, including microelectronics, microelectromechanical systems (MEMSs), nanotechnologies, molecular biology, and biotechnology with chemistry, are used to operate optical biosensors. A portable and handheld optical biosensing device would provide fast and reliable results for the identification and quantitation of pathogenic virus particles in each sample. In the modern day, the integration of intelligent nanomaterials in the developed devices provides much more sensitive and highly advanced sensors that may produce the results in no time and eventually help clinicians and doctors enormously. This review accentuates the existing challenges engaged in converting laboratory research to real-world device applications and optical diagnostics methods for virus infections. The review's background and progress are expected to be insightful to the researchers in the sensor field and facilitate the design and fabrication of optical sensors for life-threatening viruses with broader applicability to any desired pathogens.

Recent Advances in Biomedical Photonic Sensors: A Focus on Optical-Fibre-Based Sensing

In this invited review, we provide an overview of the recent advances in biomedical photonic sensors within the last five years. This review is focused on works using optical-fibre technology, employing diverse optical fibres, sensing techniques, and configurations applied in several medical fields. We identified technical innovations and advancements with increased implementations of optical-fibre sensors, multiparameter sensors, and control systems in real applications. Examples of outstanding optical-fibre sensor performances for physical and biochemical parameters are covered, including diverse sensing strategies and fibre-optical probes for integration into medical instruments such as catheters, needles, or endoscopes.

Fabrication of Humidity-Resistant Optical Fiber Sensor for Ammonia Sensing Using Diazo Resin-Photocrosslinked Films with a Porphyrin-Polystyrene Binary Mixture

Ammonia gas sensors were fabricated via layer-by-layer (LbL) deposition of diazo resin (DAR) and a binary mixture of tetrakis(4-sulfophenyl)porphine (TSPP) and poly(styrene sulfonate) (PSS) onto the core of a multimode U-bent optical fiber. The penetration of light transferred into the evanescent field was enhanced by stripping the polymer cladding and coating the fiber core. The electrostatic interaction between the diazonium ion in DAR and the sulfonate residues in TSPP and PSS was converted into covalent bonds using UV irradiation. The photoreaction between the layers was confirmed by UV-vis and Fourier transform infrared spectroscopy. The sensitivity of the optical fiber sensors to ammonia was linear when exposed to ammonia gases generated from aqueous ammonia solutions at a concentration of approximately 17 parts per million (ppm). This linearity extended up to 50 ppm when the exposure time (30 s) was shortened. The response and recovery times were reduced to 30 s with a 5-cycle DAR/TSPP+PSS (as a mixture of 1 mM TSPP and 0.025 wt% PSS in water) film sensor. The limit of detection (LOD) of the optimized sensor was estimated to be 0.31 ppm for ammonia in solution, corresponding to approximately 0.03 ppm of ammonia gas. It is hypothesized that the presence of the hydrophobic moiety of PSS in the matrix suppressed the effects of humidity on the sensor response. The sensor response was stable and reproducible over seven days. The PSS-containing U-bent fiber sensor also showed superior sensitivity to ammonia when examined alongside amine and non-amine analytes.

Optical Fibre-Based Sensors for Oil and Gas Applications

Oil and gas (O&G) explorations moving into deeper zones for enhanced oil and gas recovery are causing serious safety concerns across the world. The sensing of critical multiple parameters like high pressure, high temperature (HPHT), chemicals, etc., are required at longer distances in real-time. Traditional electrical sensors operate less effectively under these extreme environmental conditions and are susceptible to electromagnetic interference (EMI). Hence, there is a growing demand for improved sensors with enhanced measurement capabilities and also sensors that generates reliable data for enhanced oil and gas production. In addition to enhanced oil and gas recovery, the sensing technology should also be capable of monitoring the well bore integrity and safety. The sensing requirements of the O&G industry for improved sensing in deeper zones include increased transmission length, improved spatial coverage and integration of multiple sensors with multimodal sensing capability. This imposes problems like signal attenuation, crosstalks and cross sensitivities. Optical fibre-based sensors are expected to provide superior sensing capabilities compared to electrical sensors. This review paper covers a detailed review of different fibre-optic sensing technologies to identify a feasible sensing solution for the O&G industry.

Optoelectronic Instrumentation and Measurement Strategies for Optical Chemical (Bio)Sensing

There is a growing interest in the development of sensitive, portable, and low-cost instrumentation for optical chemical (bio)sensing. Such instrumentation can allow real-time decision-making for industry, farmers, and researchers. The combination of optical fiber schemes, luminescence spectroscopy techniques, and new materials for sensor immobilization has allowed the growth of optical sensors. This article focuses on the development of low-cost optoelectronic instrumentation and measurement strategies for optical chemical (bio)sensing. Most of the articles in this field have focused on the chemical sensors themselves, although few have covered the design process for optoelectronic instrumentation. This article tries to fill this gap by presenting designs for real applications, as carried out by the authors. We also offer an introduction to the optical devices and optical measurement techniques used in this field to allow a full understanding of the applications.

Plasmonic sensors based on tilted Bragg gratings in multicore optical fibers

Bare and gold-coated tilted fiber Bragg gratings (TFBGs) can nowadays be considered as a mature technology for volume and surface refractometric sensing, respectively. As for other technologies, a continuous effort is made towards the production of even more sensitive sensors, thereby enabling a high-resolution screening of the surroundings and the possible detection of rare events. To this aim, we study in this work the development of TFBG refractometers in 4-core fibers. In particular, we show that the refractometric sensitivity of the cut-off mode can reach 100 nm/RIU for a bare grating. Using another demodulation method, a tenfold sensitivity increase is obtained when tracking the extremum of the SPR (surface plasmon resonance) envelope for a gold-coated TFBG configuration. Immobilization of DNA probes was performed as a proof-of-concept to assess the high surface sensitivity of the device.

Harmonic optical microfiber Bragg grating immunosensor for the accelerative test of cardiac biomarker (cTn-I)

Fiber-optic biosensor has shown tremendous promise in probing cardiac biomarkers label-free and in-operando. However, temperature cross-sensitivity is ubiquitously found and impedes further advances of the fiber-optic biosensors, especially for the scenario of rapid test at-body. In this study, we exploit a new regime that harnesses the harmonic resonances of a single microfiber Bragg grating to rule out the impact of the thermal noise. The reflections yielded by the harmonics can be engineered simultaneously at the two overriding optical wavebands, i.e., 1 μm and 1.55 μm, promising a remote acquisition of the sensing signals at patient by virtue of the Yb and/or Er-doped fiber amplifiers which are highly commercial. Furthermore, the functionality of the temperature-offset allows for the understanding of the biomolecular stimulating at the body temperature and thus facilitating the acceleration of the cardiac biomarker test. The proposed proof-of-concept enriches the arsenal of tools for fiber biosensors and enables a vista for the instant and in-vivo diagnosis of acute heart diseases.

Microwave-photonic optical fiber interferometers for refractive index sensing with high sensitivity and a tunable dynamic range

We propose and demonstrate an extremely simple yet novel sensing strategy for measurements of a refractive index (RI) based on microwave-photonic optical fiber interferometry. A hybrid interferometric system based on an incoherent optical interferometer (i.e., a Michelson interferometer [MI]) and a coherent optical interferometer (i.e., a Fabry-Perot interferometer [FPI]) is constructed simply by using a low-cost off-the-shelf fiber coupler. The sensing arm of the MI is highly sensitive to a surrounding RI based on Fresnel reflection, where variations of the ambient RI cause changes in both the reflection magnitudes of the resonance frequencies and fringe visibility of the reflection spectra in the microwave domain. The coherent FPI is employed to tune the dynamic range of the MI by adjusting the effective reflectance of the reference arm of the MI. Essentially, other approaches that can vary the reflectance of the reference arm of the MI can also be used to tune the dynamic range of the system based on the proposed strategy. The experimental results are in good agreement with theoretical predictions. The prominent advantages of the sensor, including low cost, ease of fabrication, robustness, compactness, high sensitivity, and tunable dynamic range, make it a strong candidate in various chemical, biological, and environmental applications.

Self-referencing optical fiber pH sensor for marine microenvironments

This study presents the development of an optical fiber pH sensor based on evanescent wave absorbance for continuous pH measurements in marine microenvironments. The sensing layer consists of an optimized sol-gel matrix of tetraethoxysilane and dimethyldiethoxysilane, which substantially improves the entrapment efficiency of the pH indicator meta-cresol purple, leading to a long useable lifetime. The optical fiber pH sensor conforms to the Global Ocean Acidification Observing Network "weather" measurement quality guideline with precision of approximately 0.02 pH units, has a dynamic pH_T range of 7.4-9.7 in seawater, a response time of 2.5-6.5 min and a useable lifetime of 7 days. The optical fiber pH sensor has additional advantages of being self-referencing, without the need of an external sensor reference, having a simple fabrication method and basic spectrometer instrumentation. The suitability of the optical fiber pH sensor was demonstrated in real-time measurements of the ecologically significant green seaweed Ulva sp. The optical fiber pH sensor monitored pH variations due to metabolic activity over 7 days within the seaweed canopy and 4 days within the diffusion boundary layer interface, demonstrating the suitability for measurements in marine microenvironments.

Swelling-Based Distributed Chemical Sensing with Standard Acrylate Coated Optical Fibers

Distributed chemical sensing is demonstrated using standard acrylate coated optical fibers. Swelling of the polymer coating induces strain in the fiber’s silica core provoking a local refractive index change which is detectable all along an optical fiber by advanced distributed sensing techniques. Thermal effects can be discriminated from strain using uncoated fiber segments, leading to more accurate strain readings. The concept has been validated by measuring strain responses of various aqueous and organic solvents and different chain length alkanes and blends thereof. Although demonstrated on a short range of two meters using optical frequency-domain reflectometry, the technique can be applied to many kilometer-long fiber installations. Low-cost and insensitive to corrosion and electromagnetic radiation, along with the possibility to interrogate thousands of independent measurement points along a single optical fiber, this novel technique is likely to find applications in environmental monitoring, food analysis, agriculture, water quality monitoring, or medical diagnostics.

Microscale diamond protection for a ZnO coated fiber optic sensor

Fiber optic sensors are widely used in environmental, biological and chemical sensing. Due to the demanding environmental conditions in which they can be used, there is a risk of damaging the sensor measurement head placed in the measuring field. Sensors using nanolayers deposited upon the fiber structure are particularly vulnerable to damage. A thin film placed on the surface of the fiber end-face can be prone to mechanical damage or deteriorate due to unwanted chemical reactions with the surrounding agent. In this paper, we investigated a sensor structure formed with a Zinc Oxide (ZnO) coating, deposited by Atomic Layer Deposition (ALD) on the tip of a single-mode fiber. A nanocrystalline diamond sheet (NDS) attached over the ZnO is described. The diamond structure was synthesized in a Microwave Plasma Assisted Chemical Vapor Deposition System. The deposition processes of the nanomaterials, the procedure of attaching NDS to the fiber end-face covered with ZnO, and the results of optical measurements are presented.

Point-of-Care Diagnostics in Coagulation Management

This review provides a comprehensive and up-to-date overview of point-of-care (POC) devices most commonly used for coagulation analyses in the acute settings. Fast and reliable assessment of hemostasis is essential for the management of trauma and other bleeding patients. Routine coagulation assays are not designed to visualize the process of clot formation, and their results are obtained only after 30-90 m due to the requirements of sample preparation and the analytical process. POC devices such as viscoelastic coagulation tests, platelet function tests, blood gas analysis and other coagulometers provide new options for the assessment of hemostasis, and are important tools for an individualized, goal-directed, and factor-based substitution therapy. We give a detailed overview of the related tests, their characteristics and clinical implications. This review emphasizes the evident advantages of the speed and predictive power of POC clot measurement in the context of a goal-directed and algorithm-based therapy to improve the patient's outcome. Interpretation of viscoelastic tests is facilitated by a new visualization technology.

Integrated evanescent field detector for ultrafine particles-theory and concept

Recent studies on ultrafine particles (UFP), which are smaller than 100 nm, emphasized their hazardous potential to the human organism. They are comparable in size to typical nano-organisms such as viruses and can penetrate physiological barriers in a similar way. Currently, there are no low-cost and miniaturized detectors for UFP available. In our first experiments with an integrated evanescent field particle detector, we could already successfully detect single 200 nm polystyrene latex (PSL) spheres, although the implemented waveguide geometry was only rudimentary optimized with costly 3D simulations. We developed a fast and structured optimization model for waveguide geometry and operation wavelength of an integrated evanescent field particle detector in order to exploit its full potential for the detection of discrete analytes in the UFP size range. The optimization model is based on a modified formulation of Mie theory and its computational effort is reduced by a factor of 100 compared to 3D simulations. The optimization potential of the sensor response signal is demonstrated for several waveguide geometries that can be produced with established semiconductor fabrication technology at high production volumes and low costs. An optimized silicon nitride waveguide features sensor response signals that are about one order of magnitude higher compared to previous experiments, which pushes the limit of detection even further down to particle sizes below 100 nm. A small integrated evanescent field particle detector based on this optimized waveguide will be used for the first low-cost and miniaturized devices that can monitor the personal exposure to UFP.

Repetitive Detection of Aromatic Hydrocarbon Contaminants with Bioluminescent Bioreporters Attached on Tapered Optical Fiber Elements

In this study, we show the repetitive detection of toluene on a tapered optical fiber element (OFE) with an attached layer of Pseudomonas putida TVA8 bioluminescent bioreporters. The bioluminescent cell layer was attached on polished quartz modified with (3-aminopropyl)triethoxysilane (APTES). The repeatability of the preparation of the optical probe and its use was demonstrated with five differently shaped OFEs. The intensity of measured bioluminescence was minimally influenced by the OFE shape, possessing transmittances between 1.41% and 5.00%. OFE probes layered with P. putida TVA8 were used to monitor liquid toluene over a two-week period. It was demonstrated that OFE probes layered with positively induced P. putida TVA8 bioreporters were reliable detectors of toluene. A toluene concentration of 26.5 mg/L was detected after <30 min after immersion of the probe in the toluene solution. Additional experiments also immobilized constitutively bioluminescent cells of E. coli 652T7, on OFEs with polyethyleneimine (PEI). These OFEs were repetitively induced with Lauria-Bertani (LB) nutrient medium. Bioluminescence appeared 15 minutes after immersion of the OFE in LB. A change in pH from 7 to 6 resulted in a decrease in bioluminescence that was not restored following additional nutrient inductions at pH 7. The E. coli 652T7 OFE probe was therefore sensitive to negative influences but could not be repetitively used.

Estimation of Hg(II) in Soil Samples by Bioluminescent Bacterial Bioreporter E. coli ARL1, and the Effect of Humic Acids and Metal Ions on the Biosensor Performance

Mercury is a ubiquitous environmental pollutant of dominantly anthropogenic origin. A critical concern for human health is the introduction of mercury to the food chain; therefore, monitoring of mercury levels in agricultural soil is essential. Unfortunately, the total mercury content is not sufficiently informative as mercury can be present in different forms with variable bioavailability. Since 1990, the use of bioreporters has been investigated for assessment of the bioavailability of pollutants; however, real contaminated soils have rarely been used in these studies. In this work, a bioassay with whole-cell bacterial bioreporter Escherichia coli ARL1 was used for estimation of bioavailable concentration of mercury in 11 soil samples. The bioreporter emits bioluminescence in the presence of Hg(II). Four different pretreatments of soil samples prior to the bioassay were tested. Among them, laccase mediated extraction was found to be the most suitable over water extraction, alkaline extraction, and direct use of water-soil suspensions. Nevertheless, effect of the matrix on bioreporter signal was found to be severe and not possible to be completely eliminated by the method of standard addition. In order to elucidate the matrix role, influences of humic acid and selected metal ions present in soil on the bioreporter signal were tested separately in laboratory solutions. Humic acids were found to have a positive effect on the bioreporter growth, but a negative effect on the measured bioluminescence, likely due to shading and Hg binding resulting in decreased bioavailability. Each of the tested metal ions solutions affected the bioluminescence signal differently; cobalt (II) positively, iron (III) negatively, and the effects of iron (II) and nickel (II) were dependent on their concentrations. In conclusion, the information on bioavailable mercury estimated by bioreporter E. coli ARL1 is valuable, but the results must be interpreted with caution. The route to functional bioavailability bioassay remains long.

Fabrication and ex vivo evaluation of activated carbon-Pt microparticle based glutamate biosensor

As one of the most abundant neurotransmitters in the brain and the spinal cord, glutamate plays many important roles in the nervous system. Precise information about the level of glutamate in the extracellular space of living brain tissue may provide new insights on fundamental understanding of the role of glutamate in neurological disorders as well as neurophysiological phenomena. Electrochemical sensor has emerged as a promising solution that can satisfy the requirement for highly reliable and continuous monitoring method with good spatiotemporal resolution for characterization of extracellular glutamate concentration. Recently, we published a method to create a simple printable glutamate biosensor using platinum nanoparticles. In this work, we introduce an even simpler and lower cost conductive polymer composite using commercially available activated carbon with platinum microparticles to easily fabricate highly sensitive glutamate biosensor using direct ink writing method. The fabricated biosensors are functionality superior than previously reported with the sensitivity of 5.73 ± 0.078 nA μM^-1 mm^-2, detection limit of 0.03 μM, response time less than or equal to 1 s, and a linear range from 1 μM up to 925 μM. In this study, we utilize astrocyte cell culture to demonstrate our biosensor's ability to monitor glutamate uptake process. We also demonstrate direct measurement of glutamate release from optogenetic stimulation in mouse primary visual cortex (V1) brain slices.

Fibre optic ratiometric fluorescence pH sensor for monitoring corrosion in concrete

In this communication a novel concept for pH sensing is introduced which is specifically adapted to monitor carbonation induced corrosion in concrete structures. The method is based on a ratiometric measurement principle, exploiting the pH sensitive colour switching of thymol blue in the basic pH regime and the emissive properties of two different (Zn)CdSe/ZnS core shell quantum dots. The transition point of thymol blue in a Hydrogel D4 matrix was determined to be at around pH 11.6, which fits ideally to the intended application. Next to the fundamental spectroscopic characterization of the ratiometric response, a new design for a sensor head, suitable for the incorporation into concrete matrices is presented. Toward this, a manufacturing process was developed which includes the preparation of a double layer of polymers containing either thymol blue or a quantum dot mixture inside a porous ceramic tube. Results of a proof-of-priciple performance test of the sensor head in solutions of different pH and in cement specimens are presented, with encouraging results paving the way for future field tests in concrete.

What biologists want from their chloride reporters – a conversation between chemists and biologists

Impaired chloride transport affects diverse processes ranging from neuron excitability to water secretion, which underlie epilepsy and cystic fibrosis, respectively. The ability to image chloride fluxes with fluorescent probes has been essential for the investigation of the roles of chloride channels and transporters in health and disease. Therefore, developing effective fluorescent chloride reporters is critical to characterizing chloride transporters and discovering new ones. However, each chloride channel or transporter has a unique functional context that demands a suite of chloride probes with appropriate sensing characteristics. This Review seeks to juxtapose the biology of chloride transport with the chemistries underlying chloride sensors by exploring the various biological roles of chloride and highlighting the insights delivered by studies using chloride reporters. We then delineate the evolution of small-molecule sensors and genetically encoded chloride reporters. Finally, we analyze discussions with chloride biologists to identify the advantages and limitations of sensors in each biological context, as well as to recognize the key design challenges that must be overcome for developing the next generation of chloride sensors.

Biological Biosensors for Monitoring and Diagnosis

Quantification and detection of various contaminants in the ecosystem have become critically important in the past few decades due to their exhaustive use in soil and aquatic ecosystems. The contamination by both organic and inorganic contaminants in the ecosystem has drawn attention due to their persistence, biological accumulation, and toxicity. Organic contaminants reach the air, water, food, soil, and other systems through drift mechanism and have detrimental effect on various life systems after entering the food chain, thus interfering the normal biological process of the ecosystem. Inorganic contaminants have less solubility, primarily get adsorbed, and accumulate on lower sediments. The sources of both organic and inorganic contaminants include anthropogenic activities which dispose industrial and sewage effluent directly into water bodies. Most of the contaminants are very much toxic and have tumorigenic, carcinogenic, and mutagenic effect on various life-forms. Biosensors have various prospective and existing applications in the detection of these compounds in the environment by transducing a signal. It also has immense applications in the detection of different contaminants in the food industry, environmental monitoring, disease diagnosis, etc. where reliable and precise analyses are required. This chapter points out a comprehensive glimpse on different biosensors and their characteristics, operating principles, and their designs, based on transduction types and biological components. Efforts have been made to summarize various applications of biosensors in food industry, environmental monitoring, drug delivery systems, and clinical diagnostics etc.

Review of Dissolved Oxygen Detection Technology: From Laboratory Analysis to Online Intelligent Detection

Dissolved oxygen is an important index to evaluate water quality, and its concentration is of great significance in industrial production, environmental monitoring, aquaculture, food production, and other fields. As its change is a continuous dynamic process, the dissolved oxygen concentration needs to be accurately measured in real time. In this paper, the principles, main applications, advantages, and disadvantages of iodometric titration, electrochemical detection, and optical detection, which are commonly used dissolved oxygen detection methods, are systematically analyzed and summarized. The detection mechanisms and materials of electrochemical and optical detection methods are examined and reviewed. Because external environmental factors readily cause interferences in dissolved oxygen detection, the traditional detection methods cannot adequately meet the accuracy, real-time, stability, and other measurement requirements; thus, it is urgent to use intelligent methods to make up for these deficiencies. This paper studies the application of intelligent technology in intelligent signal transfer processing, digital signal processing, and the real-time dynamic adaptive compensation and correction of dissolved oxygen sensors. The combined application of optical detection technology, new fluorescence-sensitive materials, and intelligent technology is the focus of future research on dissolved oxygen sensors.

Current Trends in the Biosensors for Biological Warfare Agents Assay

Biosensors are analytical devices combining a physical sensor with a part of biological origin providing sensitivity and selectivity toward analyte. Biological warfare agents are infectious microorganisms or toxins with the capability to harm or kill humans. They can be produced and spread by a military or misused by a terrorist group. For example, Bacillus anthracis, Francisella tularensis, Brucella sp., Yersinia pestis, staphylococcal enterotoxin B, botulinum toxin and orthopoxviruses are typical biological warfare agents. Biosensors for biological warfare agents serve as simple but reliable analytical tools for the both field and laboratory assay. There are examples of commercially available biosensors, but research and development of new types continue and their application in praxis can be expected in the future. This review summarizes the facts and role of biosensors in the biological warfare agents' assay, and shows current commercially available devices and trends in research of the news. Survey of actual literature is provided.

Temperature monitorable refractometer of microfiber Bragg grating using a duet of harmonic resonances

To overcome the temperature cross-sensitivity of the microfiber Bragg grating (m-FBG) refractometer, we propose a novel refractive-index-temperature dual-sensing paradigm involving the third harmonic Bragg resonance that presents distinctive sensing characteristics. Strong resonances are obtained in both 1060 nm and 1550 nm wavebands under the modulation of the UV Talbot pattern. Moreover, higher-order transverse mode coupled resonance is also observed at the third harmonic waveband, supplementing an independent signal for enabling a sensing trio potentially. It is believed that the proposed dual-sensing paradigm would contribute to the m-FBT-based chemoprobes/bioprobes.

A Review of Methods for Fibre-Optic Distributed Chemical Sensing

Chemical sensing is of great importance in many application fields, such as medicine, environmental monitoring, and industrial process control. Distributed fibre-optic sensing received significant attention because of its unique feature to make spatially resolved measurements along the entire fibre. Distributed chemical sensing (DCS) is the combination of these two techniques and offers potential solutions to real-world applications that require spatially dense chemical measurements covering large length scales. This paper presents a review of the working principles, current status, and the emerging trends within DCS.

Optical Planar Waveguide Sensor with Integrated Digitally-Printed Light Coupling-in and Readout Elements

Optical planar waveguide sensors, able to detect and process information from the environment in a fast, cost-effective, and remote fashion, are of great interest currently in different application areas including security, metrology, automotive, aerospace, consumer electronics, energy, environment, or health. Integration of networks of these systems together with other optical elements, such as light sources, readout, or detection systems, in a planar waveguide geometry is greatly demanded towards more compact, portable, and versatile sensing platforms. Herein, we report an optical temperature sensor with a planar waveguide architecture integrating inkjet-printed luminescent light coupling-in and readout elements with matched emission and excitation. The first luminescent element, when illuminated with light in its absorption band, emits light that is partially coupled into the propagation modes of the planar waveguide. Remote excitation of this element can be performed without the need for special alignment of the light source. A thermoresponsive liquid crystal-based film regulates the amount of light coupled out from the planar waveguide at the sensing location. The second luminescent element partly absorbs the waveguided light that reaches its location and emits at longer wavelengths, serving as a temperature readout element through luminescence intensity measurements. Overall, the ability of inkjet technology to digitally print luminescent elements demonstrates great potential for the integration and miniaturization of light coupling-in and readout elements in optical planar waveguide sensing platforms.

D-Shaped POF Sensors for Refractive Index Sensing-The Importance of Surface Roughness

In this study the influence of the surface roughness on the transmission capacities of D-shaped plastic optical fibers (POFs) and sensors performance was investigated. Five D-shaped POF sensors were produced and characterized for refractive index sensing between 1.33 and 1.41. The sensors were characterized using a low-cost optical sensing system based on the variation of the transmitted light though the POF with refractive index changes (RI). Higher surface roughness increases the scattering losses through the POF and influences the sensors' performance; therefore, a balance must be attained. Generally, the best performance was achieved when the sensing region was polished with P600 sandpaper as a final polishing step. Polishing with sandpapers of lower grit size resulted in lower scattering, higher linearity of the sensor response and generally lower performance for RI sensing. A sensor resolution of 10-3-10-4 RIU, dependent on the value of the external refractive index, was obtained through simple and low-cost manufacturing procedures. The obtained results show the importance of surface roughness in the development of POF sensors which can be used in several applications, such as for water quality assessment.

Experimental studies on the sensitivity of the propagating and localized surface plasmon resonance-based tapered fiber optic refractive index sensors

In the present study, the sensitivities of the fiber optic propagating surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR)-based refractive index sensors have been evaluated experimentally for a tapered probe of different taper ratio. The tapering of the fiber probe has been carried out via a heating and stretching technique. The SPR probe has been fabricated by coating a thin film of silver over the core of the tapered optical fiber, while the LSPR probe has been prepared by the coating of the gold nanoparticles over the core of the tapered optical fiber. The increase in the taper ratio increases the sensitivity of both kinds of the probes. The experimentally obtained sensitivity has been compared with the sensitivity of the SPR-based fiber optic refractive index sensors fabricated using various techniques and reported in the literature.

Filipe CD, Didar TF. Intelligent Food Packaging: A Review of Smart Sensing Technologies for Monitoring Food Quality

Food safety is a major factor affecting public health and the well-being of society. A possible solution to control food-borne illnesses is through real-time monitoring of the food quality throughout the food supply chain. The development of emerging technologies, such as active and intelligent packaging, has been greatly accelerated in recent years, with a focus on informing consumers about food quality. Advances in the fields of sensors and biosensors has enabled the development of new materials, devices, and multifunctional sensing systems to monitor the quality of food. In this Review, we place the focus on an in-depth summary of the recent technological advances that hold the potential for being incorporated into food packaging to ensure food quality, safety, or monitoring of spoilage. These advanced sensing systems usually target monitoring gas production, humidity, temperature, and microorganisms' growth within packaged food. The implementation of portable and simple-to-use hand-held devices is also discussed in this Review. We highlight the mechanical and optical properties of current materials and systems, along with various limitations associated with each device. The technologies discussed here hold great potential for applications in food packaging and bring us one step closer to enable real-time monitoring of food throughout the supply chain.

Recent Progress in Electrochemical pH-Sensing Materials and Configurations for Biomedical Applications

pH-sensing materials and configurations are rapidly evolving toward exciting new applications, especially those in biomedical applications. In this review, we highlight rapid progress in electrochemical pH sensors over the past decade (2008-2018) with an emphasis on key considerations, such as materials selection, system configurations, and testing protocols. In addition to recent progress in optical pH sensors, our main focus in this review is on electromechanical pH sensors due to their significant advances, especially in biomedical applications. We summarize developments of electrochemical pH sensors that by virtue of their optimized material chemistries (from metal oxides to polymers) and geometrical features (from thin films to quantum dots) enable their adoption in biomedical applications. We further present an overview of necessary sensing standards and protocols. Standards ensure the establishment of consistent protocols, facilitating collective understanding of results and building on the current state. Furthermore, they enable objective benchmarking of various pH-sensing reports, materials, and systems, which is critical for the overall progression and development of the field. Additionally, we list critical issues in recent literary reporting and suggest various methods for objective benchmarking. pH regulation in the human body and state-of-the-art pH sensors (from ex vivo to in vivo) are compared for suitability in biomedical applications. We conclude our review by (i) identifying challenges that need to be overcome in electrochemical pH sensing and (ii) providing an outlook on future research along with insights, in which the integration of various pH sensors with advanced electronics can provide a new platform for the development of novel technologies for disease diagnostics and prevention.

A Brief Overview of Medical Fiber Optic Biosensors and Techniques in the Modification for Enhanced Sensing Ability

In this paper, we provide a brief overview of fiber optic biosensors for use in MedTech, specifically to aid in the diagnoses and treatment of those with chronic medical conditions. Fiber optic cables as components of biological sensors make them especially effective in biological systems that may require ultra-sensitive detection of low-frequency signals in hard to reach areas. This systematic review focuses on the differentiating factors of fiber-optic biosensors, which are tailored to apply the sensor to specific health needs. The main components of FOBS (fiber optic biosensors) such as biosensing elements, fiber optic cables, optical element enhancements, transducers, sensing strategies, photodetectors, and signal processing are covered in detail by showcasing the recent developments in modifications to these components. This paper pays particular attention to the alterations made in biosensing elements including pH elements, enzymatic elements, as well as those sensors utilizing antibodies and whole-cell bacteria. This paper reviews and discusses several published examples in the research stage of development to give the reader an overall scope of the field. The need for research on biosensing equipment is increasing, as the number of individuals with chronic diseases and the geriatric population require more effective, accurate, and mobile sensing ability and reduced invasiveness. FOBS offer a sensing solution that is accurate, tailorable to almost any clinical need, has abundant and relatively cheap material requirements, and a well-established technological base in fiber optic technology. This small price tag and large market potential make FOBS a desirable research area.

Emerging biosensor platforms for the assessment of water-borne pathogens

Pathogens are key contaminants in water that are responsible for the generation of various water-borne diseases, and include viruses, fungi, bacteria, and protozoan parasites. The pathogenic effects of these species in water depend on their shape, size, composition, and structure. The resulting water-borne diseases are a serious threat to the environment, including to humans and animals, and are directly responsible for environmental deterioration and pollution. The potential presence of these pathogens requires sensitive, powerful, efficient, and ideally real-time monitoring methods for their reproducible quantification. Conventional methods for pathogen detection mainly rely on time-consuming enrichment steps followed by biochemical identification strategies, which require assay times ranging from 24 h to up to a week. However, in recent years, significant efforts have been made towards the development of biosensing technologies enabling rapid and close-to-real-time detection of water-borne pathogens. This review summarizes recent developments in biosensors and sensing systems based on a variety of transducer technologies for water-quality monitoring, with specific focus on rapid pathogen detection.