Surface Functionalised Optical Fibre for Detection of Hydrogen Sulphide

Dysregulated production of hydrogen sulphide in the human body has been associated with various diseases including cancer, underlining the importance of accurate detection of this molecule. Here, we report the detection of hydrogen sulphide using fluorescence-emission enhancement of two 1,8-naphthalimide fluorescent probes with an azide moiety in position 4. One probe, serving as a control, featured a methoxyethyl moiety through the imide to evaluate its effectiveness for hydrogen sulphide detection, while the other probe was modified with (3-aminopropyl)triethoxysilane (APTES) to enable direct covalent attachment to an optical fibre tip. We coated the optical fibre tip relatively homogeneously with the APTES-azide fluorophore, as confirmed via x-ray photoelectron spectroscopy (XPS). The absorption and fluorescence responses of the control fluorophore free in PBS were analysed using UV-Vis and fluorescence spectrophotometry, while the fluorescence emission of the APTES-azide fluorophore-coated optical fibres was examined using a simple, low-cost optical fibre-based setup. Both fluorescent probes exhibited a significant increase (more than double the initial value) in fluorescence emission upon the addition of HS- when excited with 405 nm. However, the fluorescence enhancement of the coated optical fibres demonstrated a much faster response time of 2 min (time for the fluorescence intensity to reach 90% of its maximum value) compared to the control fluorophore in solution (30 min). Additionally, the temporal evolution of fluorescence intensity of the fluorophore coated on the optical fibre was studied at two pH values (7.4 and 6.4), demonstrating a reasonable overlap and confirming the compound pH insensitivity within this range. The promising results from this study indicate the potential for developing an optical fibre-based sensing system for HS- detection using the synthesised fluorophore, which could have significant applications in health monitoring and disease detection.

Optical Fibre-Based Sensors-An Assessment of Current Innovations

Optical fibre sensors are an essential subset of optical fibre technology, designed specifically for sensing and measuring several physical parameters. These sensors offer unique advantages over traditional sensors, making them gradually more valuable in a wide range of applications. They can detect extremely small variations in the physical parameters they are designed to measure, such as analytes in the case of biosensing. This high sensitivity allows them to detect subtle variations in temperature, pressure, strain, the refractive index of analytes, vibration, and other environmental factors with exceptional accuracy. Moreover, these sensors enable remote sensing capabilities. Since light signals are used to carry information, the sensing elements can be placed at distant or inaccessible sites and still communicate the data back to the central monitoring system without signal degradation. In recent times, different attractive configurations and approaches have been proposed to enhance the sensitivity of the optical fibre-based sensor and are briefly explained in this review. However, we believe that the choice of optical fibre sensor configuration should be designated based on the specific application. As these sensors continue to evolve and improve, they will play an increasingly vital role in critical monitoring and control applications across various industries.

Cherenkov Radiation in Optical Fibres as a Versatile Machine Protection System in Particle Accelerators

Machine protection systems in high power particle accelerators are crucial. They can detect, prevent, and respond to events which would otherwise cause damage and significant downtime to accelerator infrastructure. Current systems are often resource heavy and operationally expensive, reacting after an event has begun to cause damage; this leads to facilities only covering certain operational modes and setting lower limits on machine performance. Presented here is a new type of machine protection system based upon optical fibres, which would be complementary to existing systems, elevating existing performance. These fibres are laid along an accelerator beam line in lengths of ∼100 m, providing continuous coverage over this distance. When relativistic particles pass through these fibres, they generate Cherenkov radiation in the optical spectrum. This radiation propagates in both directions along the fibre and can be detected at both ends. A calibration based technique allows the location of the Cherenkov radiation source to be pinpointed to within 0.5 m with a resolution of 1 m. This measurement mechanism, from a single device, has multiple applications within an accelerator facility. These include beam loss location monitoring, RF breakdown prediction, and quench prevention. Detailed here are the application processes and results from measurements, which provide proof of concept for this device for both beam loss monitoring and RF breakdown detection. Furthermore, highlighted are the current challenges for future innovation.

Fibre-Optic Surface Plasmon Resonance Biosensor for Monoclonal Antibody Titer Quantification

An extraordinary optical transmission fibre-optic surface plasmon resonance biosensing platform was engineered to improve its portability and sensitivity, and was applied to monitor the concentrations of monoclonal antibodies (Mabs). By refining the fabricating procedure and changing the material of the flow cell and the components of the optical fibre, the biosensor is portable and robust to external interference. After the implementation of an effective template cleaning procedure and precise control during the fabrication process, a consistent sensitivity of 509 ± 5 nm per refractive index unit (nm/RIU) was achieved. The biosensor can detect the Mab with a limit of detection (LOD) of 0.44 µg/mL. The results show that the biosensor is a potential tool for the rapid quantification of Mab titers. The biosensor can be regenerated at least 10 times with 10 mM glycine (pH = 2.5), and consistent signal changes were obtained after regeneration. Moreover, the employment of a spacer arm SM(PEG)2, used for immobilising protein A onto the gold film, was demonstrated to be unable to improve the detecting sensitivity; thus, a simple procedure without the spacer arm could be used to prepare the protein A-based biosensor. Our results demonstrate that the fibre-optic surface plasmon resonance biosensor is competent for the real-time and on-line monitoring of antibody titers in the future as a process analytical technologies (PATs) tool for bioprocess developments and the manufacture of therapeutic antibodies.

Optical Fibre Sensor for Capillary Refill Time and Contact Pressure Measurements under the Foot

Capillary refill time (CRT) refers to the time taken for body tissue to regain its colour after an applied blanching pressure is released. Usually, pressure is manually applied and not measured. Upon release of pressure, simple mental counting is typically used to estimate how long it takes for the skin to regain its colour. However, this method is subjective and can provide inaccurate readings due to human error. CRT is often used to assess shock and hydration but also has the potential to assess peripheral arterial disease which can result in tissue breakdown, foot ulcers and ultimately amputation, especially in people with diabetes. The aim of this study was to design an optical fibre sensor to simultaneously detect blood volume changes and the contact pressure applied to the foot. The CRT probe combines two sensors: a plastic optical fibre (POF) based on photoplethysmography (PPG) to measure blood volume changes and a fibre Bragg grating to measure skin contact pressure. The results from 10 healthy volunteers demonstrate that the blanching pressure on the subject’s first metatarsal head of the foot was 100.8 ± 4.8 kPa (mean and standard deviation), the average CRT was 1.37 ± 0.46 s and the time to achieve a stable blood volume was 4.77 ± 1.57 s. For individual volunteers, the fastest CRT measured was 0.82 ± 0.11 and the slowest 1.94 ± 0.49 s. The combined sensor and curve fitting process has the potential to provide increased reliability and accuracy for CRT measurement of the foot in diabetic foot ulcer clinics and in the community.

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.

A Fibre-Optic Platform for Sensing Nitrate Using Conducting Polymers

Monitoring nitrate ions is essential in agriculture, food industry, health sector and aquatic ecosystem. We show that a conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), can be used for nitrate sensing through a process in which nitrate ion uptake leads to oxidation of PEDOT and change of its optical properties. In this study, a new platform is developed in which a single-mode fibre coated at the tip with PEDOT is used for nitrate sensing. A crucial step towards this goal is introduction of carbonate exposure to chemically reduced PEDOT to a baseline value. The proposed platform exhibits the change in optical behaviour of the PEDOT layer at the tip of the fibre as it undergoes chemical oxidation and reduction (redox). The change in optical properties due to redox switching varies with the intensity of light back reflected by the fibre coated with PEDOT. The proposed platform during oxidation demonstrates linear response for the uptake of nitrate ions in concentrations ranging between 0.2 and 40 parts per million (ppm), with a regression coefficient R2=0.97 and a detection limit of 6.7 ppm. The procedure for redox switching is repeatable as the back reflection light intensity reaches ±1.5% of the initial value after reduction.

A biophotonic approach to measure pH in small volumes in vitro: Quantifiable differences in metabolic flux around the cumulus-oocyte-complex (COC)

Unfertilised eggs (oocytes) release chemical biomarkers into the medium surrounding them. This provides an opportunity to monitor cell health and development during assisted reproductive processes if detected in a non-invasive manner. Here we report the measurement of pH using an optical fibre probe, OFP1, in 5 μL drops of culture medium containing single mouse cumulus oocyte complexes (COCs). This allowed for the detection of statistically significant differences in pH between COCs in culture medium with no additives and those incubated with either a chemical (cobalt chloride) or hormonal treatment (follicle stimulating hormone); both of which serve to induce the release of lactic acid into the medium immediately surrounding the COC. Importantly, OFP1 was shown to be cell-safe with no inherent cell toxicity or light-induced phototoxicity indicated by negative DNA damage staining. Pre-measurement photobleaching of the probe reduced fluorescence signal variability, providing improved measurement precision (0.01-0.05 pH units) compared to previous studies. This optical technology presents a promising platform for the measurement of pH and the detection of other extracellular biomarkers to assess cell health during assisted reproduction.

Separation and Detection of Escherichia coli and Saccharomyces cerevisiae Using a Microfluidic Device Integrated with an Optical Fibre

This paper describes the development of an integrated system using a dry film resistant (DFR) microfluidic channel consisting of pulsed field dielectrophoretic field-flow-fractionation (DEP-FFF) separation and optical detection. The prototype chip employs the pulse DEP-FFF concept to separate the cells (Escherichia coli and Saccharomyces cerevisiae) from a continuous flow, and the rate of release of the cells was measured. The separation experiments were conducted by changing the pulsing time over a pulsing time range of 2⁻24 s and a flow rate range of 1.2⁻9.6 μ L min - 1 . The frequency and voltage were set to a constant value of 1 M Hz and 14 V pk-pk, respectively. After cell sorting, the particles pass the optical fibre, and the incident light is scattered (or absorbed), thus, reducing the intensity of the transmitted light. The change in light level is measured by a spectrophotometer and recorded as an absorbance spectrum. The results revealed that, generally, the flow rate and pulsing time influenced the separation of E. coli and S. cerevisiae. It was found that E. coli had the highest rate of release, followed by S. cerevisiae. In this investigation, the developed integrated chip-in-a lab has enabled two microorganisms of different cell dielectric properties and particle size to be separated and subsequently detected using unique optical properties. Optimum separation between these two microorganisms could be obtained using a longer pulsing time of 12 s and a faster flow rate of 9.6 μ L min - 1 at a constant frequency, voltage, and a low conductivity.

Fibre Bragg Gratings for the Monitoring of Wooden Structures

The aim of this work was to develop and validate an experimental methodology suitable for analysing on-site the behaviour of fibre-reinforced wooden structures. The proposed measurement method is based on the application of fibre Bragg grating (FBG) strain sensors. An analysis of adhesive behaviour was performed preliminarily, which provided indications for choosing the type of adhesive and for the fibre bonding length in accordance with the volume of measurement. The first series of tests was carried out on wood samples to verify the coupling between the measuring sensor and the wood support when the latter is subject to mechanical stresses. The second investigation was done on site to test the behaviour of a historical wood floor before and after reinforcement by means of a series of tests performed using optical fibres with the Bragg grating. The optical fibre system measurements were compared to those obtained using a laser vibrometer, a measurement system of proven stability and precision. The comparison makes it possible to confirm the validity of the results and the reliability of the system for the monitoring of historic wooden structures.

Early Damage Detection in Composites during Fabrication and Mechanical Testing

Fully integrated monitoring systems have shown promise in improving confidence in composite materials while reducing lifecycle costs. A distributed optical fibre sensor is embedded in a fibre reinforced composite laminate, to give three sensing regions at different levels through-the-thickness of the plate. This study follows the resin infusion process during fabrication of the composite, monitoring the development of strain in-situ and in real time, and to gain better understanding of the resin rheology during curing. Piezoelectric wafer active sensors and electrical strain gauges are bonded to the plate after fabrication. This is followed by progressive loading/unloading cycles of mechanical four point bending. The strain values obtained from the optical fibre are in good agreement with strain data collected by surface mounted strain gauges, while the sensing regions clearly indicate the development of compressive, neutral, and tensile strain. Acoustic emission event detection suggests the formation of matrix (resin) cracks, with measured damage event amplitudes in agreement with values reported in published literature on the subject. The Felicity ratio for each subsequent loading cycle is calculated to track the progression of damage in the material. The methodology developed here can be used to follow the full life cycle of a composite structure, from manufacture to end-of-life.

A Dual Sensor for pH and Hydrogen Peroxide Using Polymer-Coated Optical Fibre Tips

This paper demonstrates the first single optical fibre tip probe for concurrent detection of both hydrogen peroxide (H₂O₂) concentration and pH of a solution. The sensor is constructed by embedding two fluorophores: carboxyperoxyfluor-1 (CPF1) and seminaphtharhodafluor-2 (SNARF2) within a polymer matrix located on the tip of the optical fibre. The functionalised fibre probe reproducibly measures pH, and is able to accurately detect H₂O₂ over a biologically relevant concentration range. This sensor offers potential for non-invasive detection of pH and H₂O₂ in biological environments using a single optical fibre.

Differences in external and internal cortical strain with prosthesis in the femur

The contact between a femoral stem prosthesis and the internal surface of the cortical bone with the stress in the interface is of crucial importance with respect to loosening. However, there are no reports of strain patterns at this site, and the main aim of the current study was to investigate differences of internal and external cortical strain in the proximal femur after insertion of a stem prosthesis. The external cortical strain of a human cadaveric femur was measured with strain gauges before and after implantation of a stem prosthesis. By use of optical fibres embedded longitudinally in the endosteal cortex, deformations at the implant–internal cortex interface could also be measured. The main external deformation during loading of the intact femur occurred as compression of the medial cortex; both at the proximal and distal levels. The direction of the principal strain on the medial and lateral aspects was close to the longitudinal axis of the bone. After resection of the femoral neck and insertion of a stem prosthesis, the changes in external strain values were greatest medially at the proximal level, where the magnitude of deformation in compression was reduced to about half the values measured on the intact specimen. Otherwise, there were rather small changes in external principal strain. However, by comparing vertical strain in the external and internal cortex of the proximal femur, there were great differences in values and patterns at all positions. The transcortical differences in strain varied from compression on one side to distraction on the other and vice versa in some of the positions with a correlation coefficient of 0.07. Our results show that differences exist between the external and internal cortical strain when loading a stem prosthesis. Hence, strain at the internal cortex does not correspond and can not be deducted from measured strain at the external cortex.

Whispering gallery modes in standard optical fibres for fibre profiling measurements and sensing of unlabelled chemical species

Whispering gallery mode resonances in liquid droplets and microspheres have attracted considerable attention due to their potential uses in a range of sensing and technological applications. We describe a whispering gallery mode sensor in which standard optical fibre is used as the whispering gallery mode resonator. The sensor is characterised in terms of the response of the whispering gallery mode spectrum to changes in resonator size, refractive index of the surrounding medium, and temperature, and its measurement capabilities are demonstrated through application to high-precision fibre geometry profiling and the detection of unlabelled biochemical species. The prototype sensor is capable of detecting unlabelled biomolecular species in attomole quantities.