Disposable Fluorescence Optical pH Sensor for Near Neutral Solutions

The design, development and performance evaluation of a fluorescence-based pH sensor for on-line measurements is presented. The pKa of the sensing element has been calculated to be 7.9, thus the sensor is suitable for measurement of near neutral solutions. The sensor consists of a low-cost disposable polymer sensing probe, in contact with the solution under test, interrogated by an optoelectronic transduction system. The pH sensitive dye is based on fluorescein O-methacrylate, which has been covalently linked to a hydrogel matrix, realized through the use of HEMA (2-hydroxyethyl methacrylate), HDDA (1,6-hexanediol diacrylate) and PEGDA (polyethylene glycol diacrylate). The optical interrogation setup, together with the electronics, has been developed to acquire and process the fluorescence signal. The sensor works over a pH range between 6.5 and 9.0. In the range between 7.0 and 8.0, the sensor shows a linear behavior with a maximum linearity error of 5%. Thanks to the good performance of the sensing element and transduction system, the short term drift of the reading (measured over 40 min) is lower than 0.15%. The measuring system also exhibits good performance in terms of response time and reproducibility

Fiber Optic Sensor Designs and Luminescence-based Methods for the detection of Oxygen and pH measurement

Optical, and especially fiber optic techniques for chemical sensing have become very attractive in recent decades for a wide variety of biomedical and industrial processes and considerable progress in research in this field has been seen, evidenced by the significant number of papers published over several decades, commercial products developed and marketed and which continuing to be produced. This work extends the body of knowledge in the field and focuses on two industrially-important ‘chemical’ measurands: the determination of pH level and oxygen concentration (O2) - both are critically important for a broad range of applications globally, in fields as diverse at the life sciences, environmental monitoring, biomedical research and thus widely across industry. The many different optical platform designs and fabrication methods that have been developed are considered, including those for commercial applications, recognizing the wide range of industrial and scientific uses, and their performance compared. Further, the effect of specific fiber structures on sensor performance, e.g. on sensitivity, response time and long-term stability, and possible applications also has been analyzed. Applications are seen in difficult and ‘niche’ measurement environments to which conventional sensors are often not well suited, taking advantage of their lightweight nature, ease of miniaturization, potential to be multiplexed and low cost. Through a discussion of representative techniques that have reached commercial development, a comprehensive and state-of-the-art view of this exciting and important field is possible

MULTICOMPOSITIONAL MOF AND MAGNETIC NANOPARTICLE-DERIVED HYBRID MATERIALS FOR FUNCTIONAL APPLICATIONS IN CATALYSIS AND BATTERY ANODE MATERIAL

Ph.DDOCTOR OF PHILOSOPH

Synthesis and Characterization of Fluorescent Silica Nanoparticles with Large Stokes Shifts for Multiplexed Assays and Imaging

Modern approaches to biological and biomedical analysis demand ever-increasing levels of sensitivity, selectivity, and throughput. This challenge has been addressed in the work described herein via the synthesis, characterization, and proofs of concept of a series of single and multidye copolymerized fluorescent silica nanoparticles with large Stokes shifts and near infrared fluorescence. The prepared fluorescent probes exhibit substantially enhanced fluorescence signals relative to their constituent dyes, good indicators of biocompatibility, and readily distinguishable fluorescence signals, promoting the simultaneous detection of multiple targets and reducing both the cost and time per assay. A novel NIR-fluorescent aminocyanine dye was designed for incorporation into silica nanoparticles, then synthesized and characterized as detailed in the second chapter. Spectroscopic characterization confirmed the intended dye structure and revealed a large Stokes shift, near infrared fluorescence, and a relatively high quantum yield, indicating the suitability of this compound for bioanalytical applications and incorporation into silica nanoparticles as either a standalone fluorophore or as a resonance energy transfer acceptor for other UV-visible dyes. In the third chapter, the incorporation of the novel dye and other commercial dyes into silica nanoparticles is discussed, along with characterization and proofs of concept for in vivo and in vitro applications of the resultant fluorescent labels. Nanoparticle synthetic approaches, dye concentrations, and surface coating densities were optimized for fluorescence intensities and biocompatibility. Nanoparticles containing single and multiple dye species were synthesized per the optimal parameters, producing a series of fluorescent tags with distinct fluorescence signatures and large Stokes shifts. Synthesized nanoparticles were characterized in terms of sizes, synthetic yields, quantum yields, limits of detection, stability, and synthetic reproducibility. The suitability of surface modified nanoparticles to in vitro and in vivo applications was demonstrated via biotin linkage to streptavidin microbeads and fluorescence microscopy imaging, hemocompatibility studies, and protein binding studies. Finally, in the fourth chapter, resonance energy transfer characteristics of multidye copolymerized nanoparticles were characterized. Energy transfer efficiencies between donor-acceptor pairs, numbers of dye molecules per nanoparticle, and average distances between dye molecules were calculated, then Förster radii for different donor-acceptor pairs were estimated using two approaches and compared

Estudio de biosensores electroquímicos basados en inmovilización enzimática

Els biosensors electroquímics són dispositius d'anàlisi que combinen l'especificitat de les reaccions bioquímiques amb la capacitat analítica de les tècniques electroquímiques. Gràcies a aquesta combinació, és possible determinar de forma ràpida, sensible i fiable diferents analits en mostres amb matrius complexes. Per tot això, l'ús de biosensors és una alternativa als mètodes clàssics d'anàlisi per a realitzar processos de control de qualitat en diferents sectors industrials. En la present Tesi, s'han desenvolupat biosensors amperomètrics enzimàtics basats en la immobilització d’oxidases sobre una interfase electroquímica de nanotubs d'òxid de titani (IV) altament ordenats (TiO2NTAs). Per a això, s'han estudiat diferents processos d'immobilització d'enzims basats en captura polimèrica i en immobilització covalent, i s'han avaluat els paràmetres analítics dels biosensors desenvolupats. En als processos de captura polimèrica, s'ha estudiat l'ús de kappa-carragenina, 2-hidroxietilmetacrilat (HEMA) i quitosà. Aquests hidrogels s'han utilitzat per a la immobilització de l'enzim glucosa oxidasa (GOx) i s'ha observat que tant el HEMA com el quitosà generen un microentorn favorable per a la conservació de l'activitat biològica de l'enzim. banda Per a la immobilització covalent, s'ha utilitzat pentafluorofenilmetacrilat (PFM) generació amb l’objectiu de generar enllaços entre les molècules d'enzim i la superfície del transductor. Per a això, s'ha modificat la superfície de la interfase electroquímica TiO2NTAs mitjançant dues tècniques de plasma: polimerització de PFM i sembrat del mateix polímer. S'ha observat que la superfície polimeritzada de PFM (ppPFM) presenta major hidrofobicitat que la superfície en la qual s'ha realitzat el sembrat de PFM (pgPFM) i que això té influència en la conformació que adopten les molècules d'enzim. Mentre que en la superfície ppPFM predominen conformacions amb baixa activitat, en la superfície pgPFM la major part de la població de les molècules de GOx adopten conformacions amb activitat catalítica. Per aquests motius, els biosensors amb sembrat per plasma de PFM presenten major sensibilitat enfront de la presència de glucosa que els biosensors basats en la polimerització de PFM. Finalment, s'han desenvolupat biosensors amperomètrics de glucosa i de glutamat amb matrius d'immobilització polimèriques i covalents: Ti/TiO2NTAs/GOx/Quitosà, Ti/TiO2NTAs/HEMA-co-EGDA/pgPFM/GOx/Quitosà i Ti/TiO2NTAs/GmOx/Quitosà. S'han realitzat determinacions sobre mostres alimentàries emprant aquests biosensors i els resultats s'han comparat amb els obtinguts amb tècniques de referència.Los biosensores electroquímicos son dispositivos de análisis que combinan la especificidad de las reacciones bioquímicas con la capacidad analítica de las técnicas electroquímicas. Gracias a esta combinación, es posible determinar de forma rápida, sensible y fiable distintos analitos en muestras con matrices complejas. Por ello, el uso de biosensores es una alternativa a los métodos clásicos de análisis para realizar procesos de control de calidad en distintos sectores industriales. En la presente Tesis, se han desarrollado biosensores amperométricos enzimáticos basados en la inmovilización de oxidasas sobre una interfase electroquímica de nanotubos de óxido de titanio (IV) altamente ordenados (TiO2NTAs). Para ello, se han estudiado diferentes procesos de inmovilización de enzimas basados en captura polimérica y en inmovilización covalente, y se han evaluado los parámetros analíticos de los biosensores desarrollados. En los procesos de captura polimérica, se ha estudiado el uso de kappa-carragenina, 2-hidroxietilmetacrilato (HEMA) y quitosano. Estos hidrogeles se han utilizado para la inmovilización del enzima glucosa oxidasa (GOx) y se ha observado que tanto HEMA como quitosano generan un microentorno favorable para la conservación de la actividad del enzima. Para la inmovilización covalente, se ha utilizado pentafluorofenilmetacrilato (PFM) con el objetivo de generar enlaces entre las moléculas de enzima y la superficie del transductor. Para ello, se ha modificado la superficie de la interfase electroquímica TiO2NTAs mediante dos técnicas de plasma: polimerización de PFM y sembrado del mismo polímero. Se ha observado que la superficie polimerizada de PFM (ppPFM) presenta mayor hidrofobicidad que la superficie en la que se ha realizado el sembrado de PFM (pgPFM) y que ello tiene influencia en la conformación que adoptan las moléculas de enzima. Mientras que en la superficie ppPFM predominan conformaciones con baja actividad, en la superficie pgPFM la mayor parte de la población de las moléculas de GOx adoptan conformaciones con actividad catalítica. Por estos motivos, los biosensores con sembrado por plasma de PFM presentan mayor sensibilidad frente a la presencia de glucosa que los biosensores basados en la polimerización de PFM. Finalmente, se han desarrollado biosensores amperométricos de glucosa y de glutamato con matrices de inmovilización poliméricas y covalentes: Ti/TiO2NTAs/GOx/Quitosano, Ti/TiO2NTAs/HEMA-co-EGDA/pgPFM/GOx/Quitosano y Ti/TiO2NTAs/GmOx/Quitosano. Se han realizado determinaciones sobre muestras alimentarias empleando estos biosensores y los resultados se han comparado con los obtenidos con técnicas de referencia.Electrochemical biosensors are analytical devices that combine the specificity of biochemical recognition processes with the analytical power of electrochemical techniques. Consequently, it is possible to perform rapid, sensitive and reliable determinations of different analytes present in complex samples. For this reason, the use of biosensors is an alternative to classical analytical methods to perform quality control processes in different industrial sectors. In this work, we have developed enzymatic amperometric biosensors based on the immobilization of oxidases on an electrochemical interface of highly ordered titanium dioxide nanotubes array (TiO2NTAs). Thus, processes of enzyme immobilization based on polymeric entrapment and covalent immobilization have been studied. The analytical parameters of these biosensors have been evaluated. For polymeric entrapment processes, kappa-carrageenan, 2-hydroxyethyl methacrylate (HEMA) and chitosan have been studied as immobilization matrices. These hydrogels have been used for the immobilization of the enzyme glucose oxidase (GOx) and it has been observed that both, HEMA and chitosan, generate a favorable microenvironment for the conservation of the activity of the enzyme. For covalent immobilization, pentafluorophenylmethacrylate (PFM) has been used in order to generate bonds between the enzyme molecules and the surface of the transducer. Thus, the electrochemical interface TiO2NTAs has been modified by two plasma techniques: polymerization of PFM and grafting of the same polymer. It has been observed that the polymerized surface of PFM (ppPFM) has a higher hydrophobicity than the surface in which the PFM has been grafted (pgPFM). Hydrophobicity has influence on the adopted enzyme molecules conformation. On the ppPFM surface, conformations with low activity predominate, and on the pgPFM surface most of the population of GOx molecules adopt conformations with catalytic activity. For these reasons, the biosensors with plasma grafted PFM show higher sensitivity in presence of glucose than the biosensors based on the PFM polymerization. Finally, amperometric glucose and glutamate biosensors with polymeric and covalent immobilization matrices have been developed: Ti/TiO2NTAs/GOx/Chitosan, Ti/TiO2NTAs/HEMA-co-EGDA/pgPFM/GOx/Chitosan and Ti/TiO2NTAs/GmOx/Chitosan. These biosensors have been used to determine the glucose and glutamate content in different food samples. The results have been compared with those obtained with reference techniques

Nanomaterials doped with lanthanide ions under extreme conditions for sensor and photonics applications

Se sintetizaron nanocristales de perovskita por medio del método sol gel, y por medio de medidas ópticas de estas nanoperovskitas dopadas con iones de neodimio (Nd), se optimizó el método de síntesis, eligiendo el tratamiento térmico adecuado durante el proceso de síntesis para la obtención nanocristales de perovskita con tamaños de cristalita entre 35 y 45 nm. A partir de aquí, se realizó una exhaustiva caracterización estructural y vibracional de estos materiales, por medio de medidas de difracción de Rayos-X y Espectroscopía Raman en condiciones ambiente y extremas de presión. Estas medidas fueron soportadas por los datos teóricos obtenidos por cálculos ab-initio, completando la caracterización de estos materiales con las propiedades elásticas. Se realizaron estudios de las emisiones en el infrarrojo tanto del neodimio como del tulio en estos nanomateriales con la temperatura, con el fin de analizar su viabilidad como sensores ópticos con la temperatura trabajando en el infrarrojo con elevadas sensibilidades relativas. Asimismo, se estudió la potencial viabilidad de estos nanomateriales dopados con neodimio en aplicaciones de bioimagen, por medio de experimentos de penetración de la emisión infrarroja del neodimio a través de una disolución que simula las propiedades de la piel humana, alcanzándose valores para la profundidad de 5.5 mm. Finalmente, se realizó un estudio de las emisiones infrarrojas Stokes y anti-Stokes del Nd en estos materiales con la presión, analizando la posible aplicación de estos nanomateriales como sensores ópticos con la presión trabajando en el rango infrarrojo. Además, se realizó un estudio teórico del campo cristalino que gobierna el comportamiento de las líneas de emisión con la presión