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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.

Temperature and humidity are essential parameters in monitoring the health of patients in critical care. An optical fibre sensor has been developed for simultaneous measurement of relative humidity (RH) and temperature at a single optical fibre tip based on the reflected intensity. Combining these measurements enables absolute humidity values to be obtained. The fibre tip is first modified with a coating of poly(allylamine hydrochloride) (PAH) / silica nanoparticles (SiO2 NPs) for relative humidity (RH) measurement and then coated with thermochromic liquid crystal (TLC) for temperature measurement. Experimental results demonstrate that the RH and temperature sensitivity are respectively 0.43 %/RH% (intensity at a wavelength of 650 nm) from 55 to 90% RH (R2 = 0.973) and 3.97 nm/°C from 28 to 46 °C (R2>0.99). Moreover, the proposed sensor has low crosstalk between each of the sensing parameters, with a response time of 3.1 s temperature (30–38 °C) and 13.2 s for relative humidity (20–80 %). In comparison to grating based optical fibre sensors the proposed sensor is low-cost with a simple manufacturing process which has the potential to find widespread use in healthcare applications.

© 1983-2012 IEEE. Development of a biocompatible pH sensor is of importance in biomedical applications, particularly for in vivo measurement, providing necessary information for clinical diagnosis and treatment such as chronic wounds and foetal acidosis. Traditional pH-indicator based optical sensors have problems of dye-leaching and photobleaching that restrict their uses in long-term monitoring. In this work, a dye-free fibre optic pH sensor is proposed consisting of a U-shape multimode optical fibre coated with a hybrid organic-inorganic composite film. The film is formed by cross-linking ethyl cellulose with a silica matrix at an optimised ethyl cellulose/silica molar ratio of 0.0065 via weakly interacted hydrogen bonding. This bonding is affected by hydrogen concentration (i.e., pH) in a solution resulting in a morphological change of the polymer aggregation presented in the silica matrix leading to refractive index change of the film. The developed sensor shows a reversible response to pH from 4.5 to 12.5 and exhibits linear correlation between transmitted light power and pH with a limit of agreement (LoA) between the sensor and a commercial probe of ±0.2 pH. For a clinically important range of pH values between 6 and 8 the LoA is ±0.1 pH. The sensor has low cross-sensitivity to temperature as the maximum interpreted pH change attributed to the power change is 0.12 pH when the temperature changes from 21 °C to 39 °C. To demonstrate biomedical relevance, the sensor is used to monitor pH of human serum. An in-house cytotoxicity assay is conducted with mouse fibroblast cell revealing that the film is not cytotoxic.

Textile-based systems are an attractive prospect for wearable technology as they can provide monitoring of key physiological parameters in a comfortable and unobtrusive form. A novel system based on multichannel optical fibre sensor probes integrated into a textile sleeve is described. The system measures the photoplethysmogram (PPG) at two wavelengths (660 and 830 nm), which is then used to calculate oxygen saturation (SpO2). In order to achieve reliable measurement without adjusting the position of the garment, four plastic optical fibre (POF) probes are utilised to increase the likelihood that a high-quality PPG is obtained due to at least one of the probes being positioned over a blood vessel. Each probe transmits and receives light into the skin to measure the PPG and SpO2. All POFs are integrated in a stretchable textile sleeve with a circumference of 15 cm to keep the sensor in contact with the subject&rsquo, s wrist and to minimise motion artefacts. Tests on healthy volunteers show that the multichannel PPG sensor faithfully provides an SpO2 reading in at least one of the four sensor channels in all cases with no need for adjusting the position of the sleeve. This could not be achieved using a single sensor alone. The multichannel sensor is used to monitor the SpO2 of 10 participants with an average wrist circumference of 16.0 &plusmn, 0.6 cm. Comparing the developed sensor&rsquo, s SpO2 readings to a reference commercial oximeter (reflectance Masimo Radical-7) illustrates that the mean difference between the two sensors&rsquo, readings is &minus, 0.03%, the upper limit of agreement (LOA) is 0.52% and the lower LOA is &minus, 0.58%. This multichannel sensor has the potential to achieve reliable, unobtrusive and comfortable textile-based monitoring of both heart rate and SpO2 during everyday life.

Highly sensitive and selective long-period grating (LPG) fiber-optic sensors modified with molecularly imprinted TiO2 nanothin films were fabricated. The films were deposited onto the surface of the optical fiber via liquid-phase deposition (LPD), using tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) as a template. Three LPG resonance bands were monitored during film deposition, which was of duration 4.5 h. Prior to template removal, heat treatment at 60 °C under high-humidity conditions led to an increase in refractive index of the TiO2 film, evidenced by changes in the central wavelengths of the attenuation bands. After template removal using HCl solution (0.01 M), the TMPyP-imprinted film-modified LPG sensor showed higher sensitivity to the template molecule than to structurally related guest molecules. This was measured at the 1st and 2nd resonance bands, with wavelengths ranging from 690 to 738 nm and 815 to 905 nm, respectively. No selective binding of the template was observed with a non-imprinted TiO2 film prepared in the same manner. Furthermore, the heat-treated imprinted films exhibited a substantial enhancement of photocatalytic activity for template irradiation. In particular, the self-cleaning property of the imprinted film-modified LPG sensor under ultraviolet irradiation led to highly efficient and selective binding to the template. The mechanism of the interaction between the template and the TiO2 matrix was investigated by UV–vis and Fourier-transform infrared (FTIR) spectroscopies. Additionally, morphological studies using scanning electron microscopy (SEM) were conducted.

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.

The widely applied capillary refill time (CRT) measurement is currently performed by manually applying pressure and using a stopwatch to record the time taken for the skin to recover its normal colour after a blanching pressure is applied. This method is highly subjective and observer-dependent. This paper presents a new, integrated optical sensor probe, combining monitoring of the capillary refilling process with the blanching pressure applied. The sensor consists of an optical fibre-based reflectance photoplethysmography (PPG) sensor to measure the reflected light signal, as well as a fibre Bragg grating (FBG) to measure the applied blanching pressure and to indicate the time when pressure is released. This sensor was applied to calculate the CRT (1.38 &plusmn, 0.66 s) of 10 healthy adult volunteers with (55.2 &plusmn, 21.8 kPa) blanching pressures. The form of the capillary refilling data was investigated by fitting using an exponential regression model (R2 &gt, 0.96). The integrated probe has the potential to improve the reliability of CRT measurements by standardising the optimum duration and magnitude of the pressure.

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).

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.

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.

A novel optical sensor probe combining monitoring of blood oxygen saturation (SpO2) with contact pressure is presented. This is beneficial as contact pressure is known to affect SpO2 measurement. The sensor consists of three plastic optical fibres (POF) used to deliver and collect light for pulse oximetry, and a fibre Bragg grating (FBG) sensor to measure contact pressure. All optical fibres are housed in a biocompatible epoxy patch which serves two purposes: (i) to reduce motion artefacts in the photoplethysmogram (PPG), and (ii) to transduce transverse loading into an axial strain in the FBG. Test results show that using a combination of pressure measuring FBG with a reference FBG, reliable results are possible with low hysteresis which are relatively immune to the effects of temperature. The sensor is used to measure the SpO2 of ten volunteers under different contact pressures with perfusion and skewness indices applied to assess the quality of the PPG. The study revealed that the contact force ranging from 5 to 15 kPa provides errors of &lt, 2%. The combined probe has the potential to improve the reliability of reflectance oximeters. In particular, in wearable technology, the probe should find use in optimising the fitting of garments incorporating this technology.

The sensitivity of a low-cost polymeric optical fibre humidity sensor based on transmittance changes due to evanescent wave absorption is reported using test measurements in an environmental chamber and of the skin. The layer-by-layer method was used to coat 30mm of the central unclad section of a multimode polymeric optical fibre with 7 layers of a hydrophilic film consisting of bilayers of poly(allylamine hydrochloride) and SiO2 mesoporous nanoparticles. Sensor characterisation shows a decrease in light transmission as relative humidity increases as a result of refractive index changes of the coating deposited onto the optical fibre which correlates with a commercial capacitive humidity sensor. The sensitivity obtained for the sensor coated with an optimum 7 layers was approximately -3.87x10-3 and -9.61x10-3 in transmittance percentage per RH percentage for the range of ~10% to ~75% RH and 90% to 97% RH, respectively. In addition, a response time of 1.5s can be seen for breath monitoring with the polymeric optical fibre humidity sensor. The proof of concept measurements made on the skin indicate that this sensor has the potential to be used to monitor humidity of the skin microenvironment within a wound dressing which can be used to provide better prognosis of healing.

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.

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.

The principle of operation of optical fibre long period grating (LPG) sensors is described. In particular, the chapter explores the use of LPGs as a chemical sensing platform, discussing the fabrication of LPGs and the various approaches that have been employed to modify the cladding of the LPG and thus sensitise the LPG. Examples of the practical application of LPG chemical sensors are provided.

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 p 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.

In this study, the ability of a long period grating (LPG) optical fiber sensor coated with a multilayer film of poly(diallyldimethyammonium chloride) (PDDA) and tetrakis(4-sulfophenyl)porphine (TSPP) to detect ammonia gas was demonstrated. The nano-assembled thin film was prepared using a layer-by-layer deposition technique. This combination of an LPG and TSPP could allow highly sensitive optical sensors that specifically bind ammonia to be fabricated. An LPG with a period of 100 μm and a PDDA/TSPP coating produced by depositing fifteen layers afforded a limit of detection of 0.67 ppm for ammonia gas. TSPP molecules in the film acted as ammonia receptors because the TSPP morphologically changed from J- or H-aggregates to free base monomers when it was deprotonated by being exposed to ammonia. Interestingly, HCl vapor could be used to increase the relative amount of J-aggregation in the TSPP and to restore the sensor response. The reversibility of the morphological change in the TSPP allowed reversible changes to occur in the properties of the coating, including the refractive index, film thickness and density, and electrostatic interactions; these influenced the transmission spectrum of the LPG.

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.

An optical fibre Bragg grating (FBG) was used to measure local strain (due to contact pressure) at the interface of a cuffed endotracheal tube (ETT) tested in a tracheal model. The tracheal model consisted of a corrugated tube. Two FBG sensors written in a single optical fibre were attached to the outside wall of the cuff of the ETT. Intracuff endotracheal pressure was measured using a digital manometer, while the contact pressure between the model trachea and the ETT was measured using Flexiforce sensors. Changes in the Bragg wavelengths in response to the inflation of the cuff of the ETT, and concomitant pressure increase, were observed to be dependent on the location of the FBGs at the corrugations, i.e., the annular peaks and troughs of the corrugated tube. The performance of both contact pressure sensors FBG and Flexiforce suggests that FBG technology is better suited to this application as it allows the measurement of contact pressures on non-uniform surfaces such as in the tracheal model.

A Long period grating (LPG) with a period of 111 μm was fabricated in the highly birefringent (Hi-Bi) optical fibre with the aim of developing a sensor for chirality measurements. The LPG sensor was exposed to different concentrations of glucose D(+) and fructose D(-) in water, which have similar structures but exhibit opposite optical rotations, i.e. chirality. The behaviour of the resonance bands of the submodes corresponding to the two orthogonal polarization states was different depending on the chirality of the compound, thus allowing discrimination between two compounds.

A layer-by-layer (LbL) approach was used for the deposition of coatings with a nano-meter thickness onto a multimode optical fibre that was bent into a U-shape with the aim of demonstrating a fibre-optic ammonia sensor. The film was composed of alternate layers of tetrakis(4-sulfophenyl)porphine, TSPP, and poly(diallyldimethylammonium chloride), PDDA, deposited using the LbL electrostatic self-assembly process. Exposure of the assembled film to ammonia induced a change in its absorption spectrum, which could be observed in the transmission spectrum of the coated U-shaped optical fibre. The sensor showed a linear sensitivity (77.7 mV/ppm) to ammonia in the concentration range 1–100 ppm.

Two highly sensitive ammonia sensors, formed by depositing coatings composed of titanium dioxide (TiO2) onto the cladding of an optical fibre sensing platform, are evaluated. A long period grating (LPG) of period 111 μm was fabricated in the core of an optical fibre so that the LPG operates at or near the phase matching turning point (PMTP). The first coating that was investigated was composed of TiO2 nanoparticles deposited by liquid phase deposition. The sensor showed high sensitivity and allowed low concentrations of ammonia in water (0.01 ppm) to be detected with a response time of less than 60 sec. The second coating was composed of TiO2 with subsequent layers of poly (allyamine hydrochloride) (PAH), and SiO2 nanospheres infused with a sensitive element composed of porphine. The ammonia adsorption to the porphine compound led to the changes in the LPG’s transmission spectrum and allowed 0.1 ppm of ammonia in water to be detected with a response time of less than 60 sec.

An evanescent-wave optical fibre sensor modified with tetrakis(4-sulfophenyl)porphine (TSPP) and poly(allylamine hydrochloride) (PAH) bilayers using an layer-by-layer (LbL) approach was tested to measure the gas emitted from human skin. Optical intensity changes at different wavelengths in the transmission spectrum of the porphyrin-based film were induced by the human skin gas and measured as sensor response. Influence of relative humidity, which can be a major interference to sensor response, was significantly different when compared to the influence of skin emanations. Responses of the current optical sensor system could be considered as composite sensor array, where different optical wavelengths act as channels that have selective response to specific volatile compounds. Data obtained from the sensor system was analyzed through principal component analysis (PCA). This approach enabled to distinguish skin odors of different people and their altered physiological conditions after alcohol consumption.

The use of bacteriorhodopsin (Br) coatings to create photosensitive optical fibre long period gratings (LPGs) is described. The response of the coated LPGs both sustained and pulsed illumination at a wavelength of 532 nm is monitored. The results show a clear response to the illumination and full recovery of the optical properties of the coating. This technique could allow the use of LPG for typifying photosensitive compounds and to develop optically controlled chemical sensors.

Biochromic films based on bacteriorhodopsin (BR) have been investigated, with especial regard to the creation of long-lived miniature optical vapour sensors working in real time, and exploiting the good reversibility of BR. Films were fabricated by dispersing nanosize fragments of BR in a hydrophilic matrix (gelatin) and their distribution was investigated using electron microscopy. It was shown that the composite films have meso- and microporosity, which allows not only the top layers of the film but the entire film volume to participate in changes of the film's optical parameters under the influence of a chemical stimulus from the environment. The influences of water vapour and ammonia on the parameters of the BR photocycle were investigated. When increasing the ambient relative humidity from 12 to 85%, the optical absorption of the films incorporating a chemical additive doubled, and the temporal characteristics of the photocycle varied by almost three orders of magnitude. On the other hand, the presence of ammonia influenced the photocycle parameters to a similar extent in an additive-free film. In both cases, the changes were completely reversible. It is thereby demonstrated that BR is a good candidate for a universal material for making the sensitive elements of fibre and integrated optical sensors and that the chemical additives can be used to confer selectivity on the response.

A novel ammonia gas sensor using a polyelectrolyte thin film composed of poly(diallyldimethylammonium chloride) (PDDA) and poly(acrylic acid) (PAA), PDDA/PAA, is demonstrated with a long-period gra...

An optical fibre chemical sensor that is insensitive to interfering parameters including temperature and surrounding refractive index is described. The sensor is based upon a Mach-Zehnder interferometer formed by a pair of identical cascaded long period gratings (LPGs), with the entire device coated with a mesoporous coating of silica nanoparticles. A functional material is infused only into the coating over the section of optical fibre separating the LPGs. The transmission spectrum of the device consists of a channeled spectrum arising from interference of the core and cladding modes within the envelope of the LPG resonance band. Parameters such as temperature, strain and surrounding refractive perturb the entire device, causing the phase of the channeled spectrum and the central wavelength of the envelope shift at the same rate. Exposure of the device to the analyte of interest perturbs only the optical characteristics of the section of fibre into which the functional material was infused, thus influencing only the phase of the channeled spectrum. Measurement of the phase of the channeled spectrum relative to the central wavelength of the envelope allows the monitoring of the concentration of the analyte with no interference from other parameters.

Sub-atomic engraving (MI), which was the first test by Dickey in quite a while, become a standard method in materials and investigative science. Inorganic materials for MI have been extensively drawn closer in light of their high solidness and toughness. In this examination, a porphyrin atom, tetrakis-(N-methyl-piridinium-4-yl)porphine (TMPyP), was utilized as a layout and TiO2 half and half film was integrated on an extensive stretch grinding (LPG) optical fiber by means of fluid stage testimony (LPD). This LPG fiber covered with a molecularly engraved TiO2 slim film gives a few focal points as far as high refractive record (RI) of TiO2 , high porosity, uniform surface and so forth. A 97 µm period LPG was composed on a solitary mode, photosensitive fiber with a cut-off frequency of 627 nm (Fibercore PS750). TiO2/TMPyP composite film was kept on the fiber through LPD for 4.5 h. Looking at the transmission range of the LPG sensor altered with a TiO2/TMPyP film when heat treatment, shows that the RI of the film was improved at 600 C under exceptionally muggy conditions. The format was expelled from the covering by lowering the LPG sensor into a watery arrangement of 0.1 M hydrochloric corrosive. Correlations of rebinding the format into the network with and without earlier treatment of 1 wt% alkali answer for the LPG were completed. The transmission spectra of the LPG sensor as TMPyP and mellitic corrosive were bounce back to the engraved film. The TMPyP-engraved TiO2 film demonstrated higher specific and delicate authoritative towards the layout atom than the non-engraved unadulterated TiO2 film. An optical fiber extensive stretch grinding (LPG) covered with an inorganic molecularly engraved slender film dependent on TiO2 was utilized to gauge progressively the photodecomposition of a natural objective compound. The TiO2 film was saved onto the LPG utilizing the fluid stage testimony strategy and its photograph reactant properties were utilized to decay a porphyrin. The standard of activity depends on the estimations of the refractive list (RI) change of the TiO2 flimsy film at the authoritative and evacuation of the engraved natural compound. The development of poly(acrylic corrosive) (PAA) and poly(allyamine hydrochloride) (PAH) multilayers on an optical fiber extensive stretch grinding (LPG) by the layer-by-layer (LbL) get together procedure for exceptionally delicate smelling salts gas recognition is accounted for. Perception of the LPG's transmission range showed that the refractive record (RI) of the PAH/PAA substitute layer film was changed on presentation to smelling salts, conceivably through an adjustment in the structure of the polyelectrolyte multilayers. PAA could go about as a receptor for official of amine mixes including smelling salts, which would prompt changes in the covering properties, for example, optical thickness (OT), film thickness/thickness and electrostatic cooperation, along these lines affecting the transmission range of the LPG. The alkali restricting depends on the corrosive base association to free carboxylic corrosive gatherings of PAA. A LPG of period 100 μm with a 7-cycle PAH/PAA covering presented to smelling salts showed a restriction of location of 10.7 ppm. Film morphology and thickness changes because of the authoritative of smelling salts gas, clarifying the detecting component, were affirmed through nuclear power minute (AFM) estimations. Ongoing checking of plasma propofol fixation is a significant objective for safe sedation. LPGs functionalized with have visitor engraved TiO2 films were utilized to test propofol location in fluid arrangements. The most minimal recognized fixation was 0.6 μM.

Optical phenomena have been employed extensively by human civilization throughout the centuries for lighting, communication, calculations, observations, etc. and have played a crucial role in industrial development. The applications of the optics increased significantly after the first demonstration of the light guiding phenomenon based on total internal reflection in the 1840s, which was the precursor for the development of modern optical fibres. In modern life, optical fibres found their niche in telecommunications and, more recently, as sensors.

The response of optical fibre long period gratings (LPGs), fabricated with precise control of the grating period to operate at or near the phase matching turning point (PMTP), to temperature was studied. The effect of the grating period on sensor performance was studied. The sensitivity of the LPG operating at the phase matching turning point to temperature was 0.99 nm/°C for 111.5 μm grating period that is ca. 7 times higher than that of an LPG operating far from turning point. The possibility of using LPG sensors to determine the thermo-optic coefficient of the surrounding material was explored.

© 2013 Lee et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Optical Fibre Long-Period Gratings Functionalised with Nano-Assembled Thin Films: Approaches to Chemical Sensing

Tapered optical fibers with nano-assembled coatings of thicknesses of order tens of nanometres were used for the detection of ammonia gas. The film coating was composed of alternate layers of tetrakis-(4-sulfophenyl) porphine (TSPP) and poly(allylamine hydrochloride) (PAH), which were deposited using the electrostatic self-assembly process (ESA). Exposure of a PAH/TSPP nano-assembled non-adiabatic tapered optical fiber with a waist diameter of 10 µm to ammonia induced significant optical changes in the transmission spectrum of the optical fiber. The fiber optic sensor showed a linear sensitivity to the concentration of ammonia in the range of 10–100 ppm, with response and recovery times less than 100 and 240 sec, respectively. The 3σ limit of detection (LOD) was estimated to be ca. 2 ppm.

A fibre optic long period grating (LPG) with a nano-assembled mesoporous coating of alternate layers of poly (allylamine hydrochloride) (PAH) and SiO 2 nanospheres was used for the development of a fibre-optic refractometer. PAH/SiO 2 films of different thickness have been deposited onto LP G in order to study the effect of the film thickness on sensor performance. The device showed a sensitivity of 1927 nm/RIU over a RI range of 1.3233–1.4906. INTRODUCTION Precise determination and control of the refractive index (RI) in real time continues to be an important task in a wide range of applications, including bio-chemical and food analysis, and environmental and industrial monitoring. The use of optical fibre gratings, both fibre Bragg gratings (FBGs) 1 and long period gratings (LPGs) 2 , has been extensively investigated for refractive index measurements since they offer wavelength-encoded information which overcomes the referencing issues associated w ith intensity based approaches. The refractive index sensitivity of LPGs arises from the de pendence of the phase matching condition upon the effective refractive index of the cladding modes, which in turn are dependent on the RI of the medium surrounding the cladding. The central wavelengths of the attenuation bands thus show a dependence upon the refractive index of the medium surrounding the cladding, with the highest sensitivity being sh own for surrounding refractive indices close to that of the cladding of the optical fibre

The transmission spectrum of a fibre optic long period grating (LPG) coated with a porous multilayer coating of thickness of order 400 nm formed from silica nanospheres is shown to exhibit a strong sensitivity to the infusion of a functional, chemically sensitive material into the coating. Subsequently, the transmission spectrum of the LPG shows sensitivity to changes in the properties of the functional material when exposed to a particular chemical species in an aqueous solution. The operation of such a device as an ammonia sensor is demonstrated, exhibiting 1 ppm sensitivity. The sensing mechanisms are discussed.

A novel approach to chemical application of long period grating (LPG) optical fibers was demonstrated, which were modified with a film nanoassembled by the alternate deposition of SiO(2) nanoparticles (SiO(2) NPs) and poly(diallyldimethyl ammonium chloride) (PDDA). Nanopores of the sensor film could be used for sensitive adsorption of chemical species in water, which induced the changes in the refractive index (RI) of the light propagating in the cladding mode of the optical fiber, with a concomitant effect on the transmission spectrum in the LPG region. The prepared fiber sensor was highly sensitive to the change in the RI of the surrounding medium and the response time was very fast within 10 s. In addition, chemical infusion into the film was tested using a porphyrin compound, tetrakis-(4-sulfophenyl)porphine (TSPP), which could be saturated within a few min. The lowest detectable concentration of the TSPP analyte was 10 microM. The TSPP infusion led to the development of well-pronounced dual resonance bands, indicating a large increase in the optical thickness of the film. The RI of the film was dramatically increased from 1.200 to ca. 1.540.

A layer-by-layer approach was used to deposit coatings of thickness of order 10 nm onto a multimode optical fibre from which the cladding had been removed, with the aim of demonstrating a fibre-optic ammonia sensor. The film was composed of alternate layers of tetrakis-(4-sulfophenyl) porphine (TSPP) and poly(diallyldimethylammonium chloride) (PDDA) deposited using the electrostatic self assembly process. Exposure of this material to ammonia induces a change in the absorption spectrum, which can be observed in the transmission spectrum of the coated optical fibre. The ammonia sensor shows a linear sensitivity in the concentration range of 0.1-50 ppm and the sensor response and recovery times were less than 30 seconds. The sensor was exposed to different chemical compounds (toluene, pyridine) in order to study the sensors selectivity.

A fibre-optic refractive index sensor based on a long period grating (LPG) with a nanoassembled mesoporous coating of alternate layers of poly(allylamine hydrochloride) (PAH) and SiO2 nanospheres was demonstrated. PAH/SiO2 coatings of different thicknesses were deposited onto an LPG operating near its phase matching turning point in order to study the effect of the film thickness and porosity on sensor performance. Three aqueous solutions of ethanol, glucose and sucrose of different concentrations were used to allow characterization of the refractive index (RI) over a wide RI range (1.3330?1.4906). The device showed a high sensitivity (1927 nm/refractive index unit) to RI changes with a response time less than 2 s. In particular, the current study suggested that the low RI of the mesoporous film, 1.20 at 633 nm, facilitates the measurement of external indices higher than that of the cladding, extending the range of operation of LPG-based RI sensors. The ability of this device to monitor, in real time, RI changes during a dilution process is demonstrated and discussed.