Sensores de fibra ótica para meios desafiantes

With the present work, the development of fiber optic sensor solutions for the application in challenging media was intended. New sensor structures based on the post-processing of optical fibers were addressed, taking into account their sensitivity to variations in the external environment. In a first stage, fiber Bragg gratings were embedded in lithium batteries, to monitor temperature in situ and operando. Due to the harsh chemical environment of the battery, fiber optic sensors revealed to be the most advantageous alternative, when comparing to the electronic sensors. Fiber sensors exhibited good sensitivities and fast responses, besides being less invasive, thus they did not compromise the battery response. Furthermore, they were chemically stable. Still in the framework of this theme, and with the objective of monitoring possible strain and pressure variations inside the batteries, new sensors based on in-line Fabry-Perot cavities have been proposed. These sensors were characterized in lateral load, strain, and temperature. In a later stage, the study focused on the development of configurations that allowed to obtain high-resolution and/or sensitivity sensors. One of such configurations was obtained by creating a hollow microsphere at the fiber tip. The sensor was used to detected concentration variations and refractive index of glycerin and water mixtures. The influence of the diaphragm size in the sensor response was also studied, as well as the temperature response. New sensors based on multimode interference have also been characterized, using a coreless silica fiber tip. First, the influence of different parameters, such as length and diameters were analyzed. The sensors were tested in different solutions of glucose and water. It was observed that the sensor diameter is a decisive factor in obtaining devices that are more sensitive to refractive index and, consequently, to concentration. The determination of the thermo-optic coefficient of water/ethanol mixtures was also addressed using a multimode fiber interferometer sensor. Finally, a multimode interferometer sensor was functionalized by depositing agarose throughout the structure, allowing to optimize the response of the sensors to the external environment.Com o presente trabalho pretendeu-se explorar soluções de sensores em fibra ótica para a aplicação em meios desafiantes. Novas estruturas sensoras baseadas em pós-processamento de fibra ótica foram abordadas, tendo em consideração a sua sensibilidade a variações do meio externo. Numa primeira etapa, foram embebidas redes de Bragg no interior de baterias de lítio, para monitorizar variações de temperatura in situ e operando. Devido ao complexo meio químico da bateria, os sensores em fibra ótica revelaram ser uma alternativa mais vantajosa em relação aos sensores elétricos, não só pela sensibilidade e rápida resposta, mas também pelo fato de não afetarem o desempenho da bateria. Além disso, os sensores usados revelaram ser pouco invasivos e quimicamente estáveis. Ainda no âmbito deste tema, e com o objetivo de monitorizar possíveis deformações e variações de pressão no interior da bateria de lítio, foram desenvolvidos novos sensores baseados em cavidades de Fabry-Perot do tipo in-line. Esses sensores foram caraterizados em pressão lateral, deformação e temperatura. Numa fase posterior, o estudo centrou-se no desenvolvimento de configurações que permitissem a obtenção de sensores com elevada resolução e/ou sensibilidade. Uma das configurações consistiu na formação de uma microesfera oca na ponta de uma fibra ótica. Esse sensor foi utilizado para detetar variações de concentração e índice de refração de misturas de glicerina e água. A influência do tamanho do diafragma na resposta do sensor também foi estudada, assim como a resposta em temperatura. Em seguida, desenvolveram-se novos sensores baseados em interferência multimodo, utilizando para tal uma ponta de fibra de sílica sem núcleo. Numa primeira abordagem analisou-se a influência de diferentes parâmetros, como o comprimento e o diâmetro dos sensores. Os sensores foram expostos a diferentes soluções de glucose e água. Verificou-se que o diâmetro do sensor é um fator decisivo para a obtenção de dispositivos mais sensíveis ao índice de refração e, consequentemente, à concentração. Foi também desenvolvido um sensor baseado em interferência multimodo que permitiu determinar o coeficiente termo-ótico de misturas de etanol e água. Por fim, procedeu-se à funcionalização de um sensor baseado em interferência multimodo através da deposição de agarose ao longo da estrutura, permitindo assim otimizar a sua resposta a variações do meio externo.Programa Doutoral em Engenharia Físic

Harnessing poly(ionic liquid)s for sensing applications

The interest in poly(ionic liquid)s for sensing applications is derived from their strong interactions to a variety of analytes. By combining the desirable mechanical properties of polymers with the physical and chemical properties of ILs, new materials can be created. The tunable nature of both ionic liquids and polymers allows for incredible diversity, which is exemplified in their broad applicability. In this article we examine the new field of poly(ionic liquid) sensors by providing a detailed look at the current state-of-the-art sensing devices for solvents, gases, biomolecules, pH, and anions

Enzymatic modulation of nanomaterials and its application to biosensing

Las páginas 156 a 173 están sujetas a confidencialidad por la autora. 182 p.La creciente demanda de dispositivos para la detección y monitorización de sustancias bio(químicas) ha llevado al estudio y desarrollo de nuevas plataformas para cubrir estas necesidades. En el ámbito de la salud, los biosensores representan la herramienta más sensible y eficaz con una amplia variedad de aplicaciones, sobre todo para su uso en el punto de medida (point-of-care). Estos dispositivos deben ser robustos, portables, sensibles y de fácil manejo. Entre las diferentes metodologías, los inmunoensayos son los más utilizados por su sensibilidad y selectividad frente a un gran número de biomarcadores de interés médico. A pesar de los ejemplos en el mercado basados en flujo lateral, todavía su integración en plataformas portables y el incremento de la sensibilidad no se han conseguido satisfactoriamente. Para abordar esta problemática, en la presente tesis doctoral se propone el estudio de la amplificación de la señal mediante el uso de reacciones enzimáticas, y su integración en una plataforma microfluídica para la fabricación de un inmunosensor fotoelectroquímico como plataforma ¿lab-on-a-chip¿. Por un lado, se estudiaron diferentes estrategias de detección y amplificación de la señal mediante la modulación enzimática de nanopartículas de sulfuro de plata y sulfuro de cadmio. Aquí, se desarrollaron tres sistemas enzimáticos para la detección de analitos de interés mediante fotoelectroquímica, fluorescencia, absorbancia y electroquimioluminiscencia. Se seleccionó la fotoelectroquímica como método de detección debido a las ventajas en cuanto a facilidad de integración en sistemas portables y alta sensibilidad. Por otro lado, se estudiaron diferentes métodos de inmovilización de anticuerpos en poliestireno para mejorar la orientación y el proceso de biorreconocimiento. Estos sustratos son transparentes y permiten su uso en dispositivos donde esté involucrada la luz. Finalmente, se diseñó una plataforma microfluídica donde se integró el poliestireno seleccionado y los electrodos serigrafiados de carbono. La validación del dispositivo se realizó mediante la ejecución del inmunoensayo acoplado al sistema de amplificación de señal enzimática para la posterior detección fotoelectroquímica.CICbiomaGUNE Tecnali

Mid-Infrared Integrated Devices for Optical Chemical Sensing

The mid-infrared (MIR) spectral range is of special interest for establishing optical chemical sensor technologies by allowing specific molecular identification and quantification, whether the sample is in a liquid, gas or solid form, in addition to providing highly sensitive, rapid, reagent-free and non-destructive detection. This thesis explores four different liquid- and gas- sensing applications and methods using MIR spectroscopy by integrating it with other technologies, such as microfluidics and fibre-optics. Firstly, fibre-optic integrated microfluidic devices were developed and tested for con- tinuous fluid monitoring. These showed good sensing capabilities for online, continuous and real-time liquid sensing in hard-to-reach locations. Next, this thesis presents the establishment and clinical testing of a novel method for continuous monitoring of the brain chemistry of traumatically brain-injured patients by MIR transmission spectroscopy. Here, the outlet of a cerebral microdialysis catheter is cou- pled to a micro flow-cell and the flowing microdialysate is continuously analysed. Clinical studies were carried out and showed the capability of this system for performing continuous patient monitoring over several hours. With further optimisation, the implementation of this system could lead to improved patient outcome. This thesis also presents a novel method and system based on MIR fibre-optic evanescent- wave spectroscopy, which enables enhanced detection of volatile organic compounds (VOCs). Here, a nanoporous silicon cladding was used to reversibly concentrate molecules close to the fibre surface, thus enhancing VOC detection. A significant increase in sen- sitivity was seen compared to that of an uncoated fibre and successful detection of three different VOCs, both independently and in binary mixtures, was achieved. Finally, this thesis introduces a simple and relatively low-cost fibre-optic sensor for in-line, real-time bioprocess monitoring. The sensor was successfully able to monitor varying concentrations of product (sophorolipids) in fermentation broth and was able to distinguish between the two types of generated product (acidic and lactonic sophorolipids). The work presented in this thesis showed that MIR-integrated sensors have great potential to provide novel and/or enhanced sensing solutions in a wide range of applications, including medical, industrial and environmental

Stimuli-responsive electrospun fibers and their applications

Stimuli-responsive electrospun nanofibers are gaining considerable attention as highly versatile tools which offer great potential in the biomedical field. In this critical review, an overview is given on recent advances made in the development and application of stimuli-responsive fibers. The specific features of these electrospun fibers are highlighted and discussed in view of the properties required for the diverse applications. Furthermore, several novel biomedical applications are discussed and the respective advantages and shortcomings inherent to stimuli-responsive electrospun fibers are addressed (136 references)

A Study of the Change in the Temperature of Maximum Density of Water and Aqueous Solutions as a function of Pressure

The aim of this research is to study the shift in the temperature of maximum density of water and aqueous solutions as a function of pressure. One of the many anomalous properties of water is that it passes through a maximum in density in the liquid state. In order to accurately measure the temperature of maximum density (Tmd), convective flow is monitored in a rectangular container containing the fluid. A temperature gradient is held across the chamber and it is cooled and heated in a quasi-steady state manner. A double cell convection pattern forms in the vicinity of the density maximum. This double cell is tracked by monitoring the temperature at selected points in the fluid. The change in temperature of maximum density due to concentration and applied pressure can be investigated using this technique. At a pressure of one atmosphere, this density maximum occurs in pure water at a temperature of 3.98 C. It is known that the temperature of maximum density decreases as the pressure increases; for pure water this occurs at a rate of 1 C per 50 bar. Experimentally the shift in the temperature of maximum density of aqueous solutions is tracked over the pressure range 1 to 100 bar. It is found that the temperature of maximum density drops as the pressure rises for all solutes studied, but that the rate of decrease changes depending on the nature of the solute. For ionic salts, the rate of decrease is steeper than that for pure water, whereas for monohydric alcohols the rate of decrease is less that that for pure water. These divergent trends become more apparent as solute concentrations increase. The behaviour of the temperature of maximum density is modelled on both macroscopic and microscopic levels. A simple macroscopic model is proposed by combining state functions for water with those of solutes. This approach predicts that the rate of decrease of the temperature of maximum density for ideal (noninteracting) mixtures as a function of pressure is less than for pure water (but not as pronounced as the change observed in the alcohol solutions). Microscopic modelling at the molecular level is done using Monte Carlo methods. Non-ideal mixtures are studied by introducing molecules whose interactions with water are either stronger or weaker than the water-water interactions. In all cases it is found that the rate of change of the temperature of maximum density as a function of pressure lessens compared to the rate for pure water. The models thus help in understanding some, but not all, of the experimental observations

A Miniaturized and Highly Sensitive Microwave Sensor Based on CSRR for Characterization of Liquid Materials

In this work, a miniaturized and highly sensitive microwave sensor based on a complementary split-ring resonator (CSRR) is proposed for the detection of liquid materials. The modeled sensor was designed based on the CSRR structure with triple rings (TRs) and a curve feed for improved measurement sensitivity. The designed sensor oscillates at a single frequency of 2.5 GHz, which is simulated using an Ansys HFSS simulator. The electromagnetic simulation explains the basis of the mode resonance of all two-port resonators. Five variations of the liquid media under tests (MUTs) are simulated and measured. These liquid MUTs are as follows: without a sample (without a tube), air (empty tube), ethanol, methanol, and distilled water (DI). A detailed sensitivity calculation is performed for the resonance band at 2.5 GHz. The MUTs mechanism is performed with a polypropylene tube (PP). The samples of dielectric material are filled into PP tube channels and loaded into the CSRR center hole; the E-fields around the sensor affect the relationship with the liquid MUTs, resulting in a high Q-factor value. The final sensor has a Q-factor value and sensitivity of 520 and 7.032 (MHz)/Er) at 2.5 GHz, respectively. Due to the high sensitivity of the presented sensor for characterizing various liquid penetrations, the sensor is also of interest for accurate estimations of solute concentrations in liquid media. Finally, the relationship between the permittivity and Q-factor value at the resonant frequency is derived and investigated. These given results make the presented resonator ideal for the characterization of liquid materials.Publicad

Sensores em fibra ótica baseados numa fibra de núcleo oco quadrado

In the current work, the development of optical fiber sensors based on an antiresonant hollow core fiber was aimed. The sensing structures were developed in a transmission configuration enhancing two antiresonance propagations, along with the multimode interference and Mach-Zehnder interference. With the objective of using these interferometric components as sensing elements, the sensor was employed in both liquid and air media. Initially, a numerical analysis was addressed to both internal and external antiresonances. A simulation on the effective refractive index of the fundamental core mode was also carried out, achieving results that are in good agreement with both numerical and theoretical models. Furthemore, a comparison between the expected and experimental transmission spectra was established observing, in an overall view, similar modulations. In a posterior stage, a characterization of the hollow square core fiber sensor was performed in glucose aqueous solutions. The sensor response was studied to variations in the refractive index, and calibrated to the wavelength range of the optical source utilized. Moreover, the influence of the sensor length was studied, observing the existance of an optimum length where the maximum sensitivity is enhanced. A temperature independent refractive index detection was also established. Still in the framework of this theme, and with the objective of monitoring the evaporation profile of volatile organic compounds, the sensor was embedded in ethanol aqueous solutions. The monitoring of the sensor response towards the solutions was carried out, allowing to successfully attain a real time variation of the ethanol concentration. Finally, the sensor was characterized to different physical parameters in an air environment, where two broadbands were used. In the first band, 1530nm - 1610nm, a characterization to the temperature, curvature, and strain was performed for the Mach-Zehnder interference, external resonance, and multimode interference. In the second broadband, 900nm - 1300nm, the external and internal resonances were characterize to both temperature and curvature. In both cases, the simultaneous measurement of the parameters under study was also proposed. The studied inline sensor revealed to be highly promising in the several experiments that were conducted, where, in many cases, stood out from other sensors that were already reported in the literature. Its reduced dimensions, high robustness, and capability to simultaneously measure different parameters, and making a temperature discrimination, without needing a complex design configuration, makes it extremely viable in the implementation on several applications.No presente trabalho pretendeu-se explorar o uso de uma fibra de núcleo oco antirressonante, como elementos sensores. Estes dispositivos foram desenvolvidos com uma configuração em transmissão, sendo a propagação efetuada através de duas antirressonâncias. Esta permitiu também o aparecimento de interferência multimodal e de Mach-Zehnder. Com o intuito de usar estas componentes interferométricas como elementos sensores, o dispositivo foi empregue tanto em meios líquidos, como no ar. Posteriormente, foi elaborada uma caracterização ao sensor de fibra de núcleo oco quadrado em soluções aquosas de glucose. A resposta deste foi estudada a variações do índice de refração, e calibrada à região espetral da fonte ótica utilizada. Além disso, foi estudada a influência do comprimento do sensor, tendo-se observado que existe um comprimento para o qual a sensibilidade atingida é otimizada. Adicionalmente, foi elaborada uma caracterização ao índice de refração com compensação da temperatura. Ainda no contexto da análise em meios líquidos, o sensor foi imergido em soluções aquosas de etanol, com o intuito de monitorizar o perfil de evaporação de compostos orgânicos voláteis. Efetuou-se uma monitorização da resposta espetral do sensor relativamente às soluções, o que permitiu obter, de forma satisfatória, uma variação em tempo real da concentração de etanol. Finalmente, realizou-se uma caracterização do sensor a diferentes parâmetros físicos, tendo-se usado duas bandas espetrais distintas. Na primeira banda, 1530nm − 1610nm, caracterizou-se a interferência de Mach-zehnder, a ressonância externa e a interferência multimodal a variações da temperatura, curvatura e tensão. Na segunda banda, 900nm − 1300nm, caracterizou-se as ressonâncias externa e interna a variações da temperatura e curvatura. Em ambos os casos, a medição simultânea dos parâmetros em estudo foi também proposta. O sensor desenvolvido revelou-se altamente promissor nas várias experiências realizadas, onde, em muitas situações, se destacou de outros sensores já reportados. Por ser um dispositivo que apresenta reduzidas dimensões, elevadas robustez, e capaz de medir simultaneamente a vários parâmetros, sem recorrer a configurações complexas, a sua implementação poderá vir ter impacto em diversas aplicações.Mestrado em Engenharia Físic

A Comprehensive Review on Food Applications of Terahertz Spectroscopy and Imaging.

Food product safety is a public health concern. Most of the food safety analytical and detection methods are expensive, labor intensive, and time consuming. A safe, rapid, reliable, and nondestructive detection method is needed to assure consumers that food products are safe to consume. Terahertz (THz) radiation, which has properties of both microwave and infrared, can penetrate and interact with many commonly used materials. Owing to the technological developments in sources and detectors, THz spectroscopic imaging has transitioned from a laboratory-scale technique into a versatile imaging tool with many practical applications. In recent years, THz imaging has been shown to have great potential as an emerging nondestructive tool for food inspection. THz spectroscopy provides qualitative and quantitative information about food samples. The main applications of THz in food industries include detection of moisture, foreign bodies, inspection, and quality control. Other applications of THz technology in the food industry include detection of harmful compounds, antibiotics, and microorganisms. THz spectroscopy is a great tool for characterization of carbohydrates, amino acids, fatty acids, and vitamins. Despite its potential applications, THz technology has some limitations, such as limited penetration, scattering effect, limited sensitivity, and low limit of detection. THz technology is still expensive, and there is no available THz database library for food compounds. The scanning speed needs to be improved in the future generations of THz systems. Although many technological aspects need to be improved, THz technology has already been established in the food industry as a powerful tool with great detection and quantification ability. This paper reviews various applications of THz spectroscopy and imaging in the food industry