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One challenge for geotechnical centrifuge testing of soil–structure interaction problems is the reliable measurement of induced structural strains/forces. This paper presents a novel application of fibre Bragg grating (FBG) sensors for strain measurement within geotechnical centrifuge tests. FBG sensors have several advantages for centrifuge testing, in particular their small size and minimal self-weight. This paper gives an overview of recently developed installation and calibration procedures for FBG sensors within buried centrifuge model structures. The effect of thermal expansion/contraction of the materials (including both the fibre and structures) is considered and assessed. The precision and reliability of the FBG sensors are demonstrated using verification tests. The application of the FBG sensors is considered for two geotechnical problems, namely, pile jacking and a ‘retaining wall’ adjacent to a tunnel (acting as a protective wall to prevent an adjacent structure from tunnelling-induced ground movement). The results demonstrate that the FBG sensors can provide reliable measurements of pile axial strains/forces and protective wall bending moments. The paper provides evidence to support the routine adoption of FBG sensors for strain/force measurement of structures in geotechnical centrifuge modelling.

An optical fibre ammonia gas sensor utilising a functionalised four-leaf-clover-shaped suspended-core fibre (SCF) is demonstrated. The fibre is functionalised by depositing a thin layer of an ammonia sensitive dye (tetraphenylporphyrin tetrasulfonic acid hydrate) (TPPS) on the wall of the inner cavities of the SCF through capillary action. An in-line fibre sensing structure is designed for light transmission through the SCF and also allows gas exchange with the atmosphere through two porous polyethylene housings. The sensing structure exhibits a temperature-dependent transmission due to the thermal expansion of the housings. A ratiometric method is applied for signal processing which is demonstrated to reduce significantly the effect of temperature change in the tested range (20-30 °C). The sensor is tested in ammonia concentration ranges from 0-10 ppm and demonstrates capability of detecting ammonia at ppb levels. The minimum tested concentration is 150 ppb in the experiment with a calculated limit of detection of 20 ppb. The sensor response time (T10-90%) is 160 s and it is demonstrated to be reusable after treatment with hydrogen chloride vapour. Numerical simulation of evanescent absorption features of such an SCF indicates that approximately 0.02% of the optical power exists in the air holes for the fundamental propagation mode. Distinctive absorption bands observed in the transmission spectrum of the fabricated sensor can also be observed in the simulated model after adding the TPPS absorption layer in the holes.

Ammonia (NH3) and carbon dioxide (CO2) are important breath biomarkers for diagnosis of renal and respiratory diseases. Simultaneous sensing of the two gases is useful for assessment of Helicobacter Pylori infection. This article introduces a multi-parameter optical fibre sensor by coating two different dyes, i.e., thymol blue and tetraphenylporphyrin tetrasulfonic acid hydrate (TPPS) into one optical fibre sensing system for multi-sensing of the two gases. The dyes are separately coated on distal ends of a 2 × 2 optical fibre coupler using the sol-gel technique. The reflection spectrum contains distinctive absorption peaks of the two dyes in the wavelength domain and hence can be analysed using a single spectrometer. The absorbance at a wavelength of 608 nm corresponding to the absorption peak of the thymol blue exhibits an exponential decrease as the CO2 concentration increases from 0 ppm to 60 000 ppm. The absorption bands at approximately 490 nm and 711 nm corresponding to the Soret band and Q-band of TPPS, respectively, show changes both in absorbance and central wavelengths in response to NH3 concentration in the range from 0 ppm to 80 ppm. The limit of detection and response time for CO2 and NH3 are 637 ppm and 0.15 ppm, 86 s and 83 s, respectively. The proposed sensor demonstrates the capability of sensing NH3 and CO2 simultaneously in a complex gas atmosphere containing other chemicals such as methanol and acetone, which are representative of industrial or metabolic compounds that may confound measurements.

Real time monitoring of bacterial attachment to medical devices provides opportunities to detect early biofilm formation and instigate appropriate interventions before infection develops. This study utilises long period grating (LPG) optical fibre sensors, incorporated into the lumen of endotracheal tubes (ETTs), to monitor in real time, Pseudomonas aeruginosa surface colonisation and biofilm formation. The wavelength shift of LPG attenuation bands was monitored for 24 h and compared with biofilm biomass, quantified using confocal fluorescence microscopy imaging. Biofilm formation was compared on uncoated ETTs and optical fibres, and on a biofilm resistant acrylate polymer, after challenge in an artificial sputum or minimal growth medium (RPMI-1640). The LPG sensor was able to detect a biofilm biomass as low as 81 μg/cm(2), by comparison with the confocal image quantification. An empirical exponential function was found to the link optical attenuation wavelength shift with the inverse of the biofilm biomass, allowing quantification of biofouling from the spectral response. Quantification from the sensor allows infection interception and early device removal, to reduce, for example, the risk of ventilator associated pneumonia.

This paper presents on the development of a tubular cardiovascular phantom system to simulate pulse transit time (PTT). The PTT defined as the delay time between two pulses in one cardiac cycle has been shown to be promising method for cuffless continuous blood pressure (BP) measurement. However most of the PTT measurement was performed on human subjects, thus giving a difficulty in validating sensor performance due to variability of BP. Therefore, a cardiovascular phantom system was proposed for simulate the PTT measurement. An electronic controlled module was developed to control pump operation for pulse generation. Plastic optical fibre (POF) sensors were used to measure the pulse signal on the flexible tube and the results were compared with an in-line pressure sensor. In this experiment, the delay time between two pulses were calculated offline using Matlab software and correlated with pulse pressure. The result demonstrate that the pulse delay time recorded by both sensors decreased with increase of pulse rate and pulse pressure. These results on the phantom study showed similar pattern to the human model, thus indicating that the system is able to simulate PTT for sensor validation purposes.

Accurate and efficient monitoring of electrical machine (EM) operating parameters, including temperature, mechanical vibration, torque and rotating speed and others that can indicate the EM health conditions is becoming ever more important in the world of electrical drives. The traditional methodology of one sensor per parameter can be theoretically replaced by a “one sensor measures all” technology, which can be achieved through the use of fibre-optic sensors (FOS). In this paper, several FOSs, which use different optical sensing principles for multiple physical parameter measurements of EMs, are reviewed. This paper also provides an insight into the major developments, and discusses the engineering challenges of FOS used for EM monitoring over the last few decades, and compares the advanced features of FOS with those of conventional sensors in use. Finally, a novel FOS-EM observer system scheme employing the Fibre Bragg Grating technique for multi-parameter monitoring of EM health is proposed, after discussion of the preceding industrial and academic FOS cases for EM applications.

This paper presents a design concept and a prototype of a polyimide-coated Fibre Bragg Grating (FBG) thermal sensor system based on a fast scan tunable laser source (up to 1 kHz sensing frequency). This system was deployed to perform a comprehensive 2-D real-time radial and axial thermal profiling of an electromagnetic coil - the short duty cycle electric machine (EM) windings. The thermal measurements were performed using an equivalent prototype consisting of an FBG interrogator, a multi-FBG string temperature sensor, power resistors (thermal objects), and conventional thermocouples used for measurement comparison. The FBG measurements of copper windings were subsequently carried out using a copper coil with FBG sensors system to map the radial and axial temperature distribution of the coil. The experimental results show that Polyimide-coated FBG sensor can be used for multi-point temperature monitoring of electromagnetic coils with a sensing temperature range of 20-200°C, a spatial resolution of 6cm, and a measurement error of ± 2%. The obtained thermal maps can be used for the identification of hot spot locations in electromagnetic coil systems.

Highly sensitive and selective long-period grating (LPG) fiber-optic sensors modified with molecularly imprinted TiO

Optical fibre sensors based on long period gratings (LPG) modified with functional coatings that can change their optical properties in response to the presence of the particular analyte have attracted much research attention. Ultimately such sensors have the capability to become highly sensitive and selective bio- and chemical sensors. In addition to the advantages of all optical fibre sensors such as miniature size, immunity to electromagnetic interference and low power consumption, LPGs offer wavelengths encoded information which eliminates the need for a reference and are mechanically robust which makes them attractive for practical application. One of the key components in LPG bio- and chemical optical fibre sensors is a capture layer that provides chemical selectivity to the target analyte. In this work, an overview of the different LPG bio- and chemical optical fibre sensors functionalised with various capture layers such as mesoporous thin films, molecularly imprinted polymers (MIPs) and metal-organic frameworks (MOFs) will be presented. Particular focus will be given to potential applications of the novel optical fibre LPG sensors in healthcare with examples of measuring biomarkers (protein M-immunoglobulin) and drug delivery (anaesthetics) in intensive care.

Colorimetric measurement is a versatile, low-cost method for bio-/chemical sensing and that has importance in biomedical applications. General carbon dioxide (CO2) sensors based on colorimetric change of a pH indicator report only one parameter at a time and are cross-sensitive to relative humidity (RH). This work describes a novel optical fiber sensor with a thin film on the distal end of the fiber, combining colorimetric measurement and a white light Fabry–Perot interferometer (FPI) for the simultaneous measurement of CO2 and RH. The CO2 sensitive dye ion-pair: thymol blue and tetramethylammonium hydroxide are encapsulated inside organically modified silica forming an extrinsic FPI cavity (refractive index of 1.501 ± 0.02 and thickness of 5.83 ± 0.09 μm). The sensor reversibly responds to 0–6% CO2 and 0–90% RH with negligible cross-sensitivity and allows measurement of both parameters simultaneously. A sensitivity of ∼0.19 nm/%RH is obtained for RH measurement based on the wavelength shift of the FPI and there is a polynomial correlation between the average intensity of selected wavelengths and the concentration of CO2. The applicability of the sensor is demonstrated by measuring the CO2 and RH exhaled from human breath with a percent error of 3.1% and 2.2% respectively compared to a commercial datalogger. A simulation model is provided for the dye-encapsulated FPI sensor allowing simulation of spectra of sensors with different film thicknesses.

This work reports an optical fibre probe functionalised with ‘cotton-shaped’ gold-silica nanostructures for relative humidity (RH) monitoring. The sensor response utilises the localised surface plasmon resonance (LSPR) of self-assembled nanostructures: gold nanospheres (40 nm) surrounded by one layer of poly (allylamine hydrochloride) and hydrophilic silica nanoparticles (10-20 nm) on the end-facet of an optical fibre via a wavelength shift of the reflected light. Sensor optimisation is investigated by varying the density of gold nanoparticles on the end-facet of an optical fibre. It is demonstrated that the plasmonic hybridisation mode appearing when the average gold interparticle distance is small (Median: 7.5 nm) is more sensitive to RH after functionalisation than the singular plasmonic mode. The plasmonic hybridisation mode sensor demonstrates a high linear regression to RH with a sensitivity of 0.63 nm/%RH and excellent reversibility. The response time (T10-90%) and recovery time (T90-10%) are calculated as 1.2 ± 0.4 s and 0.95 ± 0.18 s. The sensor shows no measurable cross-talk to temperature in the tested range between 25 °C to 40 °C and the 95% limit of agreement is 3.1%RH when compared to a commercial reference sensor. Simulation with finite element analysis reveals a polarisation-dependent plasmonic hybridisation with a redshift of plasmonic wavelength as a decrease of the interparticle distance and a higher refractive index sensitivity, which results in a high sensitivity to RH as observed in the experiment.

Highly sensitive fiber-optic ammonia gas sensors were fabricated via layer-by-layer deposition of poly(diallyldimethylammonium chloride) (PDDA) and tetrakis(4-sulfophenyl)porphine (TSPP) onto the surface of the core of a hard-clad multimode fiber that was stripped of its polymer cladding. The effects of film thickness, length of sensing area, and depth of evanescent wave penetration were investigated to clearly understand the sensor performance. The sensitivity of the fiber-optic sensor to ammonia was linear in the concentration range of 0.5–50 ppm and the response and recovery times were less than 3 min, with a limit of detection of 0.5 ppm, when a ten-cycle PDDA/TSPP film was assembled on the surface of the core along a 1 cm-long stripped section of the fiber. The sensor’s response towards ammonia was also checked under different relative humidity conditions and a simple statistical data treatment approach, principal component analysis, demonstrated the feasibility of ammonia sensing in environmental relative humidity ranging from dry 7% to highly saturated 80%. Penetration depths of the evanescent wave for the optimal sensor configuration were estimated to be 30 and 33 nm at wavelengths of 420 and 706 nm, which are in a good agreement with the thickness of the 10-cycle deposited film (ca. 30 nm).

Incorrect endotracheal tube (ETT) cuff inflation pressure causes significant problems for intubated patients. The technical development and first in vivo use of a smart ETT for measurements at the cuff-trachea interface during mechanical ventilation are described. The intra-tracheal multiplexed sensing (iTraXS) ETT contains integrated optical fibre sensors to measure contact pressure and blood perfusion. The device is tested during mechanical ventilation in a porcine model (N=6). For contact pressure, signals were obtained in all 30 measurements. For perfusion, data could be obtained in all 33 measurements. In the 3 cases where the cuff was inflated to an artificially high-level, blood occlusion is observed.

Immunoglobulin A (IgA), IgG, and IgM immunosensors based on long period gratings (LPG) are developed in this work. An LPG has the advantages of being lightweight and small size, which provide possibility to design miniaturized immunosensors for point of care antibody tests. Poly (allylamine hydrochloride) (PAH) and silica nanoparticles (SiNPs) are deposited on the surface of an LPG using a layer-by-layer method. The PAH/SiNPs matrix on the surface of LPG provides a porous surface structure, which is used to immobilise bio-receptors. Anti-IgA, anti-IgG, and anti-IgM are immobilised on the surface of three LPGs to fabricate IgA, IgG, and IgM sensors respectively. The refractive index (RI) on the surface of the LPG increases with antibody concentration, which induces wavelength shifts of the LPG’s attenuation bands. The performance tests of IgA, IgG, and IgM sensors are carried out in the ranges of 10–200 μg/ml, 1–90 μg/ml, and 10–320 μg/ml respectively, and the minimum detected concentrations achieved for all the three sensors are 10 μg/ml. The selectivity of the platform is investigated based on an IgM sensor. Preliminary results obtained in this work demonstrate that LPG-based immunosensors can achieve sufficient selectivity and suitable detection range for human serum testing.

Pulse arrival time (PAT) is the delay time between the peak of the R-wave Electrocardiogram (ECG) signal and the peak of Photoplethysmogram (PPG) signals. This method is widely exploited for continuous cuffless blood pressure measurement. In the literature, the PAT was determined based on the mean at a certain number or certain period of heartbeats, but none of them deployed a single pulse wave for PAT calculation. Therefore, in this paper, a relationship between mean PAT (15 pulses ± Standard Deviation (SD)) and instantaneous PAT (a pulse) with blood pressure (BP) was investigated on thirteen healthy male volunteers (aged between 17 to 42 years) through a pedal exercise. The PAT is grouped into three (3) categories which depend on the spatial position of the PPG signal measured; finger (PATf), wrist (PATw), and underfoot (PATt). The ECG and the PPG signals were synchronized using a Nexus-10 MK II data acquisition device and Matlab software (R 2014b) for subsequent analysis. An oscillometric cuff-based blood pressure instrument (Ostar, P2) was used as a BP reference during the experiment. Statistical analysis showed no significant difference in the |r| value between mean (15 pulses ± SD) and instantaneous PAT-BP; hence both methods are applicable for BP estimation using the PAT-BP calibration technique.

Development of an optical fibre sensor based on a long period grating functionalised with surface imprinted polymers for detection of Dabrafenib, a B-Raf inhibitor drug, in the concentration range 0-800 μg/ml is reported.

This paper presents the development of an optical-based fibre sensor system for pulse transit time (PTT) measurement. PTT is a promising method for cuffless continuous blood pressure (BP). In this study, the time delay between the R-wave peak of the Electrocardiogram (ECG) and the peak of the Photoplethysmogram (PPG) was measured and denoted as PTT. A conductive fabric based ECG electrode was deployed to measure the ECG on the chest. A plastic optical fibre (POF) was deployed as a medium to transport and receive light for PPG detection. A green LED (525 nm) was deployed as a light source to illuminate the skin tissue, and a phototransistor was deployed to measure the reflected light intensity. A cuff-based blood pressure (Ostar, P2) was used to measure blood pressure simultaneously with the PTTs. The ECG and the PPG signals were synchronized using a Nexus-10 MK II data acquisition device along with Matlab software for subsequent analysis. In this study, the PTT at three different positions (finger, wrist and foot) were recorded along with the BP measurement during a tilt table experiment. The results show that the system is able to monitor the PTT during a tilt table moving from supine position to tilt-up position (0° to 70°). A statistical analysis was performed by using SPSS software to compare the mean of BP and the PTT in supine and tilt-up position. The novelty of the developed system lies in the miniaturization of the POF system and the combination of POFs and textile electrodes that are well suited to smart textile applications.

An endotracheal tube with integrated optical fibre sensors (fibre Bragg grating and photoplethysmography) is described. The system aims to ensure the appropriate cuff inflation pressure to achieve a gas seal but reduce pressure injury.

Monitoring of key physiological and pharmacological parameters is an important part of a closed loop control system in critical care. Optical fiber sensors provide a versatile platform technology that can be easily incorporated into existing in-dwelling catheters or face masks. With appropriate functional coatings they can be used to monitor a range of relevant parameters and two different examples are presented: (i) respiration monitoring; (ii) drug level monitoring. Respiration monitoring involves monitoring of temperature and humidity in inhaled and exhaled breath. The optical fiber sensor consists of a fiber Bragg grating to measure temperature and a tip coating whose refractive index changes with humidity. The sensor is demonstrated to be able to track breath to breath changes when incorporated into a mask. Drug level monitoring is demonstrated in vitro using a long period grating coated with molecularly imprinted polymer nanoparticles that are sensitive to fentanyl. The sensor has a limit of detection of 50ng/ml.

Creatinine (CR) is a representative metabolic byproduct of muscles, and its sensitive and selective detection has become critical in the diagnosis of kidney diseases. In this study, poly(acrylic acid) (PAA)-assisted molecularly imprinted (MI) TiO2 nanothin films fabricated via liquid phase deposition (LPD) were employed for CR detection. The molecular recognition properties of the fabricated films were evaluated using fiber optic long period grating (LPG) and quartz crystal microbalance sensors. Imprinting effects were examined compared with nonimprinted (NI) pure TiO2 and PAA-assisted TiO2 films fabricated similarly without a template. In addition, the surface modification of the optical fiber section containing the LPG with a mesoporous base coating of silica nanoparticles, which was conducted before LPD-based TiO2 film deposition, contributed to the improvement of the sensitivity of the MI LPG sensor. The sensitivity and selectivity of LPGs coated with MI films were tested using CR solutions dissolved in different pH waters and artificial urine (near pH 7). The CR binding constants of the MI and NI films, which were calculated from the Benesi–Hildebrand plots of the wavelength shifts of the second LPG band recorded in water at pH 4.6, were estimated to be 67 and 7.8 M−1, respectively, showing an almost ninefold higher sensitivity in the MI film. The mechanism of the interaction between the template and the TiO2 matrix and the film composition was investigated via ultraviolet–visible and attenuated total reflectance Fourier-transform infrared spectroscopy along with X-ray photoelectron spectroscopy analysis. In addition, morphological studies using a scanning electron microscope and atomic force microscope were conducted. The proposed system has the potential for practical use to determine CR levels in urine samples. This LPG-based label-free CR biosensor is innovative and expected to be a new tool to identify complex biomolecules in terms of its easy fabrication and simplicity in methodology.

Molecularly imprinted nanoparticles (MIPs) synthesized via a solid-phase synthesis process are successfully deposited on the surface of a long period grating (LPG) optical fibre sensor for detection of fentanyl in a liquid solution. Real-time detection of fentanyl can be observed from the LPG sensor. The wavelength change of LPG sensor linearly fits the concentration of fentanyl with a sensitivity of 0.004 nm/ (ng/ml) and limit of detection of 3.75 ng/ml for concentrations up to 200 ng/ml.

Real time monitoring of plasma propofol concentration is an important goal for safe anaesthesia. LPGs functionalized with host-guest imprinted TiO2 films were used to test propofol detection in aqueous solutions. The lowest detected concentration was 0.6 μM.

An optical fibre long period grating (LPG) based volatile organic compound (VOC) sensor coated with ZIF-8, a material from the zeolite imidazolate framework (ZIF) family, functional coating is presented. ZIF-8 film was deposited onto the surface of the LPG using an in-situ crystallization technique. A concentration specific response to ethanol was obtained over the range from 62 to 666 ppm. A novel approach for the data analysis based on the measurement of the bandwidth of the U-shaped attenuation band of the LPG is introduced. The sensor shows a sensitivity of 0.018±0.0015 nm/ppm and limit of detection (LOD) of 5.56 ppm for ethanol vapour in air.

An optical fibre long period grating sensor coated with three layers of poly (allylamine hydrochloride) and silica core gold shell nanoparticles was developed for the detection of human IgM. Three different concentrations of IgM suspension (19nM, 83nM and 0.3 μM) were detected. The sensor response time is less than 8 minutes and the binding of IgM can be observed dynamically at a concentration of 0.3 μM. The binding constant of IgM on the LPG sensor is 23.9 (pM)−1 based on the fitting of the Langmuir adsorption isotherm. The sensitivity of the LPG sensor is calculated as 11 nm/ (ng/mm2) with a limit of detection of 0.0218 ng/mm2.

Trabajo presentado en la Eurosensors 2017 Conference. París, 3–6 de septiembre de 2017. An optical fiber sensor for ethanol detection in exhaled breath has been developed. It has been fabricated by functionalizing a Long Period Grating with a metal-organic framework, ZIF-8. The sensor’s response was tested by exposure to exhaled breath of a person before and after the ingestion of alcoholic drinks, showing a higher wavelength difference between the resonance bands in the second case. Further work will analyze cross-sensitivity towards temperature, relative humidity and carbon dioxide. The authors would like to acknowledge Spanish Ministry of Economy and Competitiveness for the financial support through TEC2016-78047-R project.

Optical fibre sensing is a platform technology for applications in biomedical and environmental monitoring. Fibre Bragg Gratings can be used to monitor parameters such as pressure and temperature. Alternatively, coating the fibres with functional layers, either at the tip of the fibre, on a U-shaped fibre, or a long period grating enables sensing of analytes in liquids and gases. This paper describes the application of optical fibre sensing techniques during mechanical ventilation via an endotracheal tube in critical care. Functional coatings on the fibres are used to monitor humidity of inspired air and can be used to monitor other analytes.

Contact between a medical device and tissue accounts for approximately a third of damage to soft tissue in hospitals. The use of sensors at the interface between the device and tissue can be used to maintain the optimum pressure and reduce such injuries. A sensorised endotracheal tube has been developed and is proposed as a method of reducing soft tissue damage and improving design of future devices. Optical fibre sensing is used to monitor both cuff contact pressure (via a fibre Bragg grating) and tissue perfusion (via reflectance photoplethysmography). The monitoring system developed has been used in an animal study and demonstrates reliable measurement of contact pressure and perfusion.

An array of three long period gratings (LPGs) fabricated in a single optical fibre and multiplexed in the wavelength domain was used to measure simultaneously temperature, relative humidity (RH) and volatile organic compounds (VOCs). Each LPG sensor was designed to optimize its response to a desired measurand. The LPGs were fabricated with periods such that they operated at or near the phase matching turning point. The sensors were calibrated in the laboratory and the simultaneous measurement of the key indoor air quality parameters was undertaken in laboratory and office environments. It was demonstrated successfully that the data produced by the LPG sensor array under real conditions was in a good agreement with that produced by commercially available sensors. Further, the potential application of fibre optic sensors for VOCs detection at high levels has been demonstrated.

An optical fibre long period grating (LPG) modified with a thin film of HKUST-1, a material from metal organic framework (MOF) family, was employed for the detection of carbon dioxide. The sensing mechanism is based on the measurement of the change of the refractive index (RI) of the coating that is induced by the penetration of CO 2 molecules into the HKUST-1 pores. The responses of the resonance bands in the transmission spectrum of an LPG modified with 40 layers of HKUST-1 upon exposure to carbon dioxide in mixture with nitrogen were investigated.

In this study, an optical fibre long period grating (LPG) sensor functionalised with a mesoporous thin film was employed for the identification and quality assessment of beverages. The principle of the discrimination of beverages using an LPG sensor is based on the measurement of the change in refractive index of a sensitive film, induced by the binding of the chemical compounds present in the beverage. The sensitive film deposited onto the LPG consisted of poly(allylamine hydrochloride) (PAH) and silica nanospheres (SiO2 NPs) with diameters ranging from 40 nm to 50 nm. PAH imparts selectivity, while the SiO2 NPs endow the film with high porosity and enhanced sensitivity. In this study, five different types of beverages, red and white wines, brandy, nihonshyu (sake, a Japanese rice wine), and shochu (a Japanese distilled beverage), prepared via distillation and fermentation, were used to assess the capability of the sensor to identify the origin of the beverages. In addition, a selection of red wines was used to evaluate the use of the sensor in the assessment of the quality of beverages. The results obtained were benchmarked against those obtained using gas chromatography–mass spectrometry for the determination of volatile compounds contributing to the flavours of a set of red wines. Principal component analysis (PCA) was employed for data analysis. This approach enabled both quality assessment of beverages and identification of the methods and materials used for their preparation. Keywords: Long period grating, Mesoporous thin film, Layer-by-layer, Quality assessment, Beverages

The formation of poly(acrylic acid) (PAA) and poly(allyamine hydrochloride) (PAH) multilayers on an optical fiber long period grating (LPG) by the layer-by-layer (LbL) assembly technique for highly sensitive ammonia gas detection is reported. Observation of the LPG's transmission spectrum indicated that the refractive index (RI) of the PAH/PAA alternate layer film was changed on exposure to ammonia, possibly via a change in the structure of the polyelectrolyte multilayers. PAA could act as a receptor for binding of amine compounds including ammonia, which would induce changes in the coating properties such as optical thickness (OT), film thickness/density and electrostatic interaction, thus influencing the transmission spectrum of the LPG. The ammonia binding is based on the acid–base interaction to free carboxylic acid groups of PAA. An LPG of period 100 μm with a 7-cycle PAH/PAA coating exposed to ammonia exhibited a limit of detection of 10.7 ppm. Film morphology and thickness changes due to the binding of ammonia gas, explaining the sensing mechanism, were confirmed through atomic force microscopic (AFM) measurements.

Optical fibre sensors(OFS), as a result of their unique properties such as small size, no interference with electromagnetic radiation, high sensitivity and the ability to design multiplexed or distributed sensing systems, have found applications ranging from structural health monitoring to biomedical and point of care instrumentation. While the former represents the main commercial application for OFS, there is body of literature concerning the deployment of this versatile sensing platform in healthcare. This paper reviews the different types of OFS and their most recent applications in healthcare. It aims to help clinicians to better understand OFS technology and also provides an overview of the challenges involved in the deployment of developed technology in healthcare. Examples of the application of OFS in healthcare are discussed with particular emphasis on recently (2015–2017) published works to avoid replicating recent review papers. The majority of the work on the development of biomedical OFS stops at the laboratory stage and, with a few exceptions, is not explored in healthcare settings. OFSs have yet to fulfil their great potential in health care and methods of increasing the adoption of medical devices based on optical fibres are discussed. It is important to consider these factors early in the device development process for successful translation of the developed sensors to healthcare practice.

An optical fibre sensor for simultaneous temperature and humidity measurements consisting of one fibre Bragg grating (FBG) to measure temperature and a mesoporous film of bilayers of Poly(allylamine hydrochloride)(PAH) and silica (SiO2) nanoparticles deposited onto the tip of the same fibre to measure humidity is reported. The hygroscopic film was created using the layer-by-layer (LbL) method and the optical reflection spectra were measured up to a maximum of 23 bilayers. The temperature sensitivity of the FBG was 10 pm/°C while the sensitivity to humidity was (-1.4x10-12 W / %RH) using 23 bilayers. The developed sensor was tested in the mechanical ventilator and temperature and humidity of the delivered artificial air was simultaneously measured. Once calibrated, the optical fibre sensor has the potential to control the absolute humidity as an essential part of critical respiratory care. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

A method for measuring the contact pressure between an endotracheal tube cuff and the trachea was designed and developed by using a fibre Bragg grating (FBG) based optical fibre sensor. The FBG sensor is encased in an epoxy based UV-cured cuboid patch and transduces the transversely loaded pressure into an axial strain that induces wavelength shift of the Bragg reflection. The polymer patch was created by using a PTFE based mould and increases tensile strength and sensitivity of the bare fibre FBG to pressure to 2.10×10-2 nm/kPa. The characteristics of the FBG patch allow for continuous measurement of contact pressure. The measurement of contact pressure was demonstrated by the use of a 3D printed model of a human trachea. The influence of temperature on the measurements is reduced significantly by the use of a second FBG sensor patch that is not in contact with the trachea. Intracuff pressure measurements performed using a commercial manometer agreed well with the FBG contact pressure measurements. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

A fast method for the fabrication of the long period gratings (LPG) optical fibres operating at or near the phase matching turning point (PMTP) with the period of 109.0, 109.5 and 110.0 μm based on an amplitude mask writing system is described. The proposed system allows fabricating 3 cm long LPG sensors operating at PMPT within 20 min that is approximately 8 times faster than point-by-point approach. The reproducibility of the fabrication process was thoroughly studied. The response of the fabricated LPGs to the external change of the refractive index was investigated using water and methanol.

Optical fibre sensors have the potential to be incorporated into wound dressings to monitor moisture and predict healing without the need to remove the dressing. A low cost polymeric optical fibre humidity sensor based on evanescent wave absorption is demonstrated for skin humidity measurement. The sensor is fabricated by coating the fibre with a hydrophilic film based on bilayers of Poly(allylamine hydrochloride) (PAH) and SiO 2 mesoporous nanoparticles. The Layer-by-Layer method was used for the deposition of the layers. Multimode polymeric optical fibre with a cladding diameter of 250μm was covered by 7 layers of PAH/SiO 2 film on the central region of an unclad fibre with a diameter of 190μm. The length of the sensitive region is 30mm. Experiment results show a decrease in light intensity when relative humidity increases due to refractive index changes of the fibre coating. The sensitivity obtained was 200mV/%RH and the sensor was demonstrated to provide a faster response to changes in the humidity of the skin microenvironment than a commercial sensor.

The development of an ammonia sensor, formed by the deposition of a functionalised titanium dioxide film onto a tapered optical fibre is presented. The titanium dioxide coating allows the coupling of light from the fundamental core mode to a lossy mode supported by the coating, thus creating lossy mode resonance (LMR) in the transmission spectrum. The porphyrin compound that was used to functionalise the coating was removed from the titanium dioxide coating upon exposure to ammonia, causing a change in the refractive index of the coating and a concomitant shift in the central wavelength of the lossy mode resonance. Concentrations of ammonia as small as 1ppm was detected with a response time of less than 1min. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Objective: To develop a compact probe that can be used to monitor humidity in ventilator care equipment. A mesoporous film of alternate layers of Poly(allylamine hydrochloride) (PAH) and silica (SiO2) nanoparticles (bilayers), deposited onto an optical fibre was used. The sensing film behaves as a Fabry-Perot cavity of low-finesse where the absorption of water vapour changes the optical thickness and produces a change in reflection proportional to humidity. Methods: The mesoporous film was deposited upon the cleaved tip of an optical fibre using the layer-by-layer method. The sensor was calibrated in a bench model against a commercially available capacitive sensor. The sensitivity and response time were assessed in the range from 5 % relative humidity (RH) to 95%RH for different numbers of bilayers up to a maximum of nine. Results: The sensitivity increases with the number of bilayers deposited; sensitivity of 2.28 mV/%RH was obtained for nine bilayers. The time constant of the response was 1.13 s ± 0.30 s which is faster than the commercial device (measured as 158 s). After calibration, the optical fibre humidity sensor was utilised in a bench top study employing a mechanical ventilator. The fast response time enabled changes in humidity in individual breaths to be resolved. Conclusion: Optical fibre sensors have the potential to be used to monitor breath to breath humidity during ventilator care. Significance: Control of humidity is an essential part of critical respiratory care and the developed sensor provides a sensitive, compact and fast method of humidity monitoring.

A highly sensitive and fast method for electrochemical detection of 2,3-dimethyldinitrobutane (DMNB) on a graphite working electrode modified with a TiO2 thin film including single-walled carbon nanotubes (SWCNTs) is proposed. Incorporation of the SWCNTs into the inorganic matrix allowed the preparation of a highly stable film with an integrated electrochemical chip. The sensing mechanism is based on the current change generated at the specific voltage due to the redox reaction of the DMNB NO2 functional group. The detection limit and sensitivity were significantly improved due to the interaction between the SWCNTs and the analyte, which considerably enhanced the electron transferability. Under the optimized conditions, the linear range of the DMNB detection was 10 ppb to 10 ppm with a detection limit of 12 ppb, showing a sensitivity of 61 nA ppb -1 .

In this work a new optical fibre sensor for the detection of aromatic carboxylic acids (ACAs) is proposed. The operation of the sensor is based on the measurement of the change in refractive index of a functional coating deposited onto the cladding of the optical fibre. Mesoporous thin films were fabricated using the layer-by-layer self-assembly of poly(allylamine hydrochloride) (PAH) and silica nanospheres (SiO 2 ) with a diameter in the range of 40–50 nm. The film was successfully deposited onto three different transducers; an optical fibre long-period grating (LPG), a quartz crystal microbalance (QCM) and a silicon wafer used in reflectometric interference spectroscopy (RIfS). The amino (NH 2 ) functional group of PAH was used as the binding site for the detection of ACAs. High sensitivity, with binding constants of 1.36 ± 0.01 × 10 6 and 5.6 ± 0.01 × 10 8 M −1 for benzoic acid and mellitic acid, respectively, was achieved. The lowest measured concentration of 1 nM of mellitic acid was achieved selectively over structurally (phenol) and functionally (acetic acid) related compounds. Concomitant refractive index (RI) and QCM mass changes were measured to validate the LPG response.

A fibre optic long period grating (LPG) with an nano-assembled mesoporous coating of alternate layers of poly(diallyldimethylammonium chloride) (PDDA) and SiO 2 nanospheres was used for the development of a highly sensitive fibre-optic chemical sensor. Sensor fabrication involves a 2-stage process: firstly, the deposition of the base mesoporous thin film (PDDA/SiO 2 ) over an LPG written in the optical fibre using a layer-by layer technique, followed by the infusion of a functional material into the porous film. The refractive index of the base mesoporous coating, determined at a wavelength of 633 nm using ellipsometry, was found to be 1.2. The infusion of the functional material into the coating resulted in a significant change in the RI of the coating, producing a dramatic change in the transmission spectrum of the LPG. The sensing mechanism exploited is based upon chemically induced desorption of the functional material from the mesoporous coating. The sensing of ammonia in aqueous solution was chosen as an example to demonstrate the sensing principle of the LPG sensor. The operation of the sensor was characterized using two functional materials, tetrakis-(4-sulfophenyl)porphine (TSPP) and polyacrylic acid (PAA). The device showed high sensitivity to ammonia with a response time less than 100 s and a limit of detection of 140 ppb when the TSPP infused (PDDA/SiO 2 ) film was employed as a sensitive element.

Nano-assembled thin films prepared by a layer-by-layer approach on QCM resonators were used as sensitive elements for monitoring relative humidity. Different types of films, polymer-based (PDDA/PSS)n film and porphyrin-based (PDDA/TSPP)n and (PDDA/MnTSPP)n films (where n = 5, 10, and 15), showed linear responses to relative humidity changes in the range of 4–94%. Increase of the number of bilayers deposited on the QCM electrode enhanced the sensitivity to relative humidity. The porphyrin-based films showed ca. 4.5 times higher sensitivity towards relative humidity than the polymer-based films, owing to presence of the higher number of free sulfonic acid groups. Incorporation of the metal ion into the porphyrin pyrrole ring was not significant in sensitivity. However, all films showed a good reversibility to the stepwise changes of relative humidity and the response and recovery times (t90) were very fast within 15 s.

Quartz crystal microbalance (QCM) gas sensors based on the alternate adsorption of TiO(2) and polyacrilic acid (PAA) were developed for the sensitive detection of amine odors. Individual TiO(2) gel layers could be regularly assembled with a thickness of approximately 0.3 nm by the gas-phase surface sol-gel process (GSSG). The thickness of the poly(acrylic acid) (PAA) layer is dependent on its molecular weight, showing different thicknesses of approximately 0.4 nm for PAA(25) (Mw 250,000) and 0.6-0.8 nm for PAA(400) (Mw 4,000,000). The QCM sensors showed a linear response to ammonia in the concentration range 0.3-15 ppm, depending on the deposition cycle of the alternate TiO(2)/PAA layer. The ammonia binding is based on the acid-base interaction to the free carboxylic acid groups of PAA and the limit of detection (LOD) of the 20-cycle TiO(2)/PAA(400) film was estimated to be 0.1 ppm when exposed to ammonia. The sensor response was very fast and stable in a wide relative humidity (rH) range of 30-70%, showing almost the same frequency changes at a given concentration of ammonia. Sensitivity to n-butylamine and ammonia was higher than to pyridine, which is owing to the difference of molecular weight and basicity of the amine analytes. The alternate TiO(2)/PAA(400) films have a highly effective ability to capture amine odors, and the ambient ammonia concentration of 15 ppm could be condensed up to approximately 20,000 ppm inside the films.

GC–MS analysis based on purge and trap sampling followed by Curie point thermal desorption was examined for the quantitative determination of 2,4,6-trichloroanisole in aqueous solutions. The method developed showed linearity in single ion monitoring mode over a TCA concentration range of 0.12–120 ng L−1 (parts-per-trillion).

The practical fabrication of thin-film chemical sensors generally requires the responsive element to be embedded in a matrix. The influence of different organic and inorganic matrices (polyvinyl alcohol (PVA), gelatin, and silica) on the static and dynamic optical properties of bacteriorhodopsin (bR)-containing films, including their responses to ammonia, were studied. Morphological and cross-sectional studies of the bR-containing films using atomic force microscopy, scanning electron microscopy, and energy dispersive spectroscopy revealed a uniform distribution of the bR within the films; the silica films were much rougher and more porous than those made with the polymers; gelatin tended to suppress the ammonia response (because of its amine groups); PVA and silica greatly slowed down the photocycle (because of their hydroxyl groups). The silica-based film had the fastest and most sensitive response to ammonia.

The optical response of optical fibres end-coated with bacteriorhodopsin-containing films to ammonia vapour was investigated. Both static absorptance changes and changes in the dynamic parameters of the actinic light-induced photocycle were determined. Simple optical adsorption measurements can be used to detect ammonia with a detection limit of 5 ppm and a dynamic range of 10–10,000 ppm, over which the response is logarithmic. By analysing the modulation of the photocycle response by ammonia, the limit of detection can be decreased to 0.9 ppm. The incorporation of chemicals with an amine functionality, such as triethanolamine, in the film suppresses the ammonia response, and is therefore useful for referencing.