Com o desenvolvimento e o aumento do uso de combustíveis renováveis, surge também a necessidade de garantir sua produção e distribuição com a qualidade especificada. Desta forma, tornou-se imprescindível o estudo de metodologias eficazes para determinar as propriedades físico-químicas de forma rápida e não destrutiva, possibilitando a sua aplicação ao controle de qualidade no monitoramento on/in/at-line dos combustíveis em ambiente industrial. Na literatura, as espectroscopias de infravermelho, próximo (NIR) e médio (mid-IR), têm sido exaustivamente combinadas as ferramentas quimiométricas para determinação de propriedades de misturas diesel-biodiesel. Contudo, a inclusão da aplicação da espectroscopia Raman pode oferecer praticidade aos ensaios e contribuir na construção de instrumentos de baixo custo para controle de qualidade de combustíveis e biocombustíveis. Neste cenário, o presente estudo tem como objetivo apresentar modelos de previsão das propriedades de combustíveis (diesel) e biocombustíveis (biodiesel), puros e de suas misturas, baseados em técnicas espectroscópicas (NIR, mid-IR e Raman) acopladas com ferramentas quimiométricas, as quais se inclui a utilização de técnicas de seleção de variáveis combinadas com mínimos quadrados parciais (PLS) e a aplicação de florestas aleatórias (RF) e máquina de vetores de suporte (SVM) para as propriedades não lineares. Na primeira parte do estudo (banco 1), o índice de refração e a massa específica de 148 amostras de biodiesel foram determinados usando dados espectroscópicos. Na segunda parte do estudo (banco 2), o ponto de entupimento de filtro de frio (PEFF) e a viscosidade cinemática a 40˚C de 333 amostras de biodiesel, diesel, diesel-biodiesel e misturas de diesel-biodiesel-etanol foram determinados usando dados espectroscópicos. Para ambos os estudos, 80 % das amostras formaram o conjunto de calibração e 20% formaram o conjunto de validação. Os resultados mostraram que o modelo PLS obtido com os espectros mid-IR e intervalos selecionados pelo algoritmo UVE forneceu a melhor previsão para o índice de refração, com 5 variáveis latentes, raiz quadrada do erro médio quadrático (RMSEP) igual a 1,0∙10-4 e coeficiente de determinação da previsão (R2pred) igual a 0,95. O melhor modelo de previsão para a massa específica foi obtido pelo método RF com os espectros de mid-IR, com RMSEP igual 1,16∙10-4 g∙cm-3 e R2pred igual a 0,98. Para a previsão do PEFF, o melhor modelo foi obtido com SVM em espectros mid-IR e intervalos selecionados pelo algoritmo RC, com RMSEP igual a 0,7˚C e R2pred igual a 0,94. O melhor modelo de previsão da viscosidade cinemática a 40˚C foi obtido pelo método RF com os espectros de mid-IR, com RMSEP igual a 0,0184 mm2∙s-1 e R2pred igual a 0,98. Os resultados deste estudo mostraram que os espectros de mid-IR foram os mais adequados na previsão das propriedades estudadas. A figura de mérito Soma das probabilidades do teste de Wilcoxon (SWTP) desenvolvida neste estudo foi imprescindível para a escolha do melhor modelo.

O biodiesel tem sido amplamente utilizado como uma fonte de energia renovável, que contribui para a diminuição de demanda por diesel mineral. Portanto, existem várias propriedades que devem ser monitoradas, a fim de produzir e distribuir biodiesel com a qualidade exigida. Neste trabalho, as propriedades físicas do biodiesel, tais como massa específica, índice de refração e ponto de entupimento de filtro a frio foram medidas e associadas a espectrometria no infravermelho próximo (NIR) e espectrometria no infravermelho médio (Mid-IR) utilizando ferramentas quimiométricas. Os métodos de regressão por mínimos quadrados parciais (PLS), regressão de mínimos quadrados parciais por intervalos (iPLS), e regressão por máquinas de vetor de suporte (SVM) com seleção de variáveis por Algoritmo Genético (GA) foram utilizadas para modelar as propriedades mencionadas. As amostras de biodiesel foram sintetizadas a partir de diferentes fontes, tais como canola, girassol, milho e soja. Amostras adicionais de biodiesel foram adquiridas de um fornecedor da região sul do Brasil. Em primeiro lugar, o pré-processamento de correção de linha de base foi usado para normalizar os dados espectrais de NIR, seguidos de outros tipos de pré-processamentos que foram aplicados, tais como centralização dos dados na média, 1ª derivada e variação de padrão normal. O melhor resultado para a previsão do ponto de entupimento de filtro a frio foi utilizando os espectros de Mid-IR e o método de regressão GA-SVM, com alto coeficiente de determinação da previsão, R2Pred=0,96 e baixo valor da Raiz Quadrada do Erro Médio Quadrático da previsão, RMSEP (°C)= 0,6. Para o modelo de previsão da massa específica, o melhor resultado foi obtido utilizando os espectros de Mid-IR e regressão por PLS, com R2Pred=0,98 e RMSEP (g/cm3)= 0,0002. Quanto ao modelo de previsão para o índice de refração, o melhor resultado foi obtido utilizando os espectros de Mid-IR e regressão por PLS, com excelente R2Pred=0,98 e RMSEP= 0,0001. Para esses conjuntos de dados, o PLS e o SVM demonstraram sua robustez, apresentando-se como ferramentas úteis para a previsão das propriedades do biodiesel estudadas

Under the same conditions of turbidity (transmittance = 50%) the average amounts of feces per unit smear area are increased when diluents with high refractive indices are substituted for water. Such increments, calculated as factors, were on the average: 3.17 for 54% sucrose (n = 1.438); 1.95 for 50% glycerol (n = 1.411); and 1.50 for 30% sucrose (n = 1.385) aqueous solutions. Photoelectric absorptiometry was found adequate for evaluating the efficiency of fecal smear clearing processes.

The Localised Surface Plasmon Resonance (LSPR)-based sensors have become a leading label-free biosensing technology. Despite their prominence, these sensors still require refinement in key areas, including sensitivity, specificity, repeatability, reproducibility and configuration adaptable for point-of-care biosensing. In this dissertation, work was undertaken to improve these parameters by developing LSPR sensors in Optical Fibre (OF) in a reflection configuration. In order to achieve this objective, the following tasks were contemplated: synthesis of Gold Nanoparticles (AuNPs) of 3 different sizes (20, 40, and 80 nm); morphological and stability analysis of the NPs; production of OF probes with a 600 μm diameter; comparison of two silanes for binding AuNPs to OF (APTES vs MPTMS). Additionally, tests were conducted on the repeatability, reproducibility, and characterisation of the probes, assessing their absorbance spectrum as a function of the of surrounding environment’s Refractive Index (RI). Finally, the OF-LSPR approach with the best sensitivity and reproducibility was biofunctionalised with antibodies to test the performance of these probes as biosensors. Overall, the results showed that the probes functionalized with smaller AuNPs exhibited the best performance, achieving an average sensitivity of 3.96±0.32 Arb.u./R.I.u. over the widest consistent response range 1.3342-1.3356 R.I.u.. Repeatability and reproducibility were statistically evaluated using the Intraclass Correlation Coefficient 3 (ICC3), resulting in values of ICC3 ≥ 0.98 for both figures of merit. These results supported the viability of this approach, which combines the advantages of LSPR phenomena with the versatility of the OF reflection configuration. Subsequently, a pilot immunoassay test for Human Serum Albumin (HSA) demonstrated that the developed biosensor identifies analyte concentrations in an operating range of 0.001-10 ng/mL, with an average sensitivity of (10.5±1.9)× 10⁻⁴ Arb.u./log(ng/mL). This research corroborates and expands the existing literature, laying the foundations for methodological advances in LSPR biodetection. The inherent versatility and affordable cost of the developed immunosensor, combined with its suitability for direct, real-time monitoring of molecular interactions in low-volume samples, positions it for future integration into point-of-interest biodetection applications.

In this work, a hybrid sensor based on a section of hollow square core fiber (HSCF) spliced between two single mode fibers is proposed for the measurement of refractive index of liquids. The sensor, with a length of a few millimeters, operates in a transmission configuration. Due to the HSCF inner geometry, two different interferometers are generated. The first, a Mach-Zehnder interferometer, is insensitive to the external refractive index, and presents a sensitivity to temperature of (29.2 ± 1.1) pm/°C. The second one, a cladding modal interferometer, is highly sensitive to the external refractive index. An experimental resolution of 1.0 × 10-4 was achieved for this component. Due to the different responses of each interferometer to the parameters under study, a compensation method was developed to attain refractive index measurements that are temperature independent. The proposed sensor can find applications in areas where refractive index measurements are required and the control of room temperature is a challenge, such as in the food and beverage industry, as well as in biochemical or biomedical industries.

The application of spectroscopic ellipsometry for the characterization of UV-patterned channel waveguides to obtain the refractive index contrast and surface deformation profile is presented. Thin films were prepared with organic-inorganic di-ureasils hybrids modified with zirconium tetra-propoxide deposited in silica on silicon substrates. The channel waveguides were produced by direct writing using UV laser radiation. The refractive index contrast and the surface ablation induced by the UV optical signal were estimated by ellipsometry being 4.5 x 10(-3) and 30.5 nm, respectively. The deepness of the surface ablation due to the UV exposition was also estimated by atomic force microscopy measurements that pointed out a value of 31.0 +/- 1.0 nm, concordant with the ellipsometric calculations. The near-field intensity technique was used as a support for contextualizing the proposed ellipsometry method for the characterization of refractive index profiles. The estimated refractive index contrast (2.0 x 10(-3)) is in a good agreement with the refractive index contrast derived from ellipsometry.

Several research groups have been proposing different dispersion compensation schemes, for very high-speed (greater than or equal to40 Gbit/s) long-haul systems operating in the C-band window (1530-1563 nm) over standard single mode fibers, known as ITU-T G.652 fibers. The focus on these high chromatic dispersion fibers is due to the large amount of standard single mode fibers already installed in the field. Although several dispersion compensation techniques have proved to be successful, the long term stability of this kind of systems remains to be seen. In fact, when in the field, these high speed systems present a very unstable behavior, which is translated in large variations of the bit error rate. In order to stabilize the systems strong forward error correction codes have been used. In this work, we prove quantitatively that this inherent instability is mainly due to chromatic dispersion variations induced by temperature swings. Two models for the chromatic dispersion and chromatic dispersion slope variations with temperature are developed and validated using laboratory measurements previously published. After the effect of temperature change is analyzed in terms of eye opening penalty, it is shown that for systems operating at 40 Gbit/s and above temperature effects have to be considered in system design. (C) 2004 Elsevier B.V. All rights reserved.

A fiber-optic refractive index (RI) sensor based on a long period fiber grating (LPFG) coated with a zinc oxide (ZnO) thin film was fabricated and characterized. A method to overcoat the LPFG’s with a homogeneous ZnO thin films was developed. Characterization of ZnO thin films, deposited simultaneously on silicon (Si) planar substrates, was performed using Scanning Electron Microscope, Energy Dispersive X-ray Spectroscopy and X-ray Photoelectron Spectroscopy. The LPFGs with ZnO coatings from 29 to 145 nm of thickness were characterized and compared in terms of the wavelength shift and the intensity of the attenuation bands changing the surrounding refractive index (SRI) from 1.300 to 1.600. An average wavelength sensitivity of ∼7162 nm/RIU was achieved in the RI range from 1.440 to 1.456 and more than 12,000 nm/RIU at 1.440 RI. Using a ZnO film thickness of 116 nm and in the RI region between 1.320 and 1.360 the average sensitivity of ∼806 nm/RIU was measured for a 145 nm thick film. Working as an intensity sensing device, the 87 nm coated LPFG shows a linear sensitivity of 216.4 dB/RIU in a wide range of RI from 1.340 to 1.420.

<jats:p>This work describes a 3D-printed optofluidic fiber sensor to measure refractive index in real time, combining a microfluidic system with an optical fiber extrinsic Fabry–Perot interferometer. The microfluidic chip platform was developed for this purpose through 3D printing. The Fabry–Perot cavity was incorporated in the microfluidic chip perpendicularly to the sample flow, which was of approximately 3.7 µL/s. The optofluidic fiber sensor platform coupled with a low-cost optical power meter detector was characterized using different concentrations of glucose solutions. In the linear regression analysis, the optical power shift was correlated with the refractive index and a sensitivity of −86.6 dB/RIU (r2 = 0.996) was obtained. Good results were obtained in terms of stability with a maximum standard deviation of 0.03 dB and a sensor resolution of 5.2 × 10−4 RIU. The feasibility of the optofluidic fiber sensor for dynamic analyses of refractive index with low sample usage was confirmed through real-time measurements.</jats:p>

The ubiquity and importance of anions in many crucial roles accounts for the current high interest in the design and preparation of effective sensors for these species. Therefore, a tilted fiber Bragg grating sensor was fabricated to investigate individual detection of different anion concentrations in ethyl acetate, namely acetate, fluoride and chloride. The influence of the refractive index on the transmission spectrum of a tilted fiber Bragg grating was determined by developing a new demodulation method. This is based on the calculation of the standard deviation between the cladding modes of the transmission spectrum and its smoothing function. The standard deviation method was used to monitor concentrations of different anions. (...)