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Perovskite solar cells have garnered significant interest thanks to the impressive rise of their efficiency over the last few years to a power conversion efficiency (PCE) of 25.2% despite being processable using cheap and potentially high-throughput solution coating techniques. Using the two-step conversion process high-quality perovskite films with high quality and uniformity can be produced, however, this process still needs a deeper and fundamental understanding. This thesis has shed light on the ink-to-solid conversion during the two-step solution process of hybrid perovskite formulations. We demonstrated that the conversion of PbI2 to perovskite is largely dictated by the state of the PbI2 precursor film in terms of its solvated states. We used several in situ diagnostic measurments such as grazing incidence wide-angle x-ray scattering (GIWAXS), quartz crystal microbalance with dissipation monitoring (QCM-D), and optical reflectance and absorbance all performed during spin coating, to monitor the nucleation and growth of crystalline phases, the mass deposition at the solid-liquid interface and the rigidity as well as the solution thinning behavior and the changes in optical absorbance of the precursor and perovskite. We compare conversion behaviors from different lead states by using methylammonium iodide (MAI), formamidinium iodide (FAI), and/or mixtures of halides (I, Br) and show that conversion can occur spontaneously and quite rapidly at room temperature without requiring further thermal annealing. We confirm this by demonstrating improvements in the morphology, microstructure and optoelectronics properties of the resulting perovskite films, as well as their impact on the PCE of solar cells using complimentary measurements such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and with steady-state photoluminescence.

Polypyrrol (PPy) ist ein typischer Vertreter der intrinsisch leitfähigen Polymere und wird auf zahlreichen Gebieten, wie Analytik, Korrosionsschutz oder Elektrotechnik angewendet. Dabei nutzt man die elektronische Schaltbarkeit, die Stabilität und die gute Oxidierbarkeit sowie die Wasserlöslichkeit der Monomere aus. Im Rahmen dieser Arbeit wurde der Einfluss verschiedener Parameter, wie Temperatur, Monomerkonzentration und Leitsalz, auf die elektrochemische Polymerisation von Pyrrol untersucht. Des Weiteren sollte die Wirkung eines statischen Magnetfeldes auf die Synthese und das Ionenaustauschverhalten überprüft werden. Als Messverfahren kamen die elektrochemische Quarzmikrowaage (EQCM) und die elektrochemische Impedanzspektroskopie (EIS) zum Einsatz. Bei der Auswertung der EQCM-Daten wurde ein von Efimov entwickeltes mathematisches Modell zur Bestimmung des komplexen Schermoduls angewendet. Dadurch war eine in situ Verfolgung der viskoelastischen Eigenschaften während der Abscheidung und des Ionenaustausches möglich. Um den hydrodynamischen Einfluss auf die Synthese von PPy zu untersuchen, wurden Messungen an einer rotierenden Scheibenelektrode durchgeführt. Die daraus gewonnenen Erkenntnisse vermittelten eine Vorstellung, wie sich eine durch den magnetohydrodynamischen Effekt hervorgerufene Rührung auf die Grenzströme der potentiostatischen Abscheidung verschiedener PPy|Leitsalz Systeme auswirkt. Ferner ist die Abscheidung von PPy aus Phosphorsäure betrachtet worden, da diese Schichten eine Relevanz für den Korrosionsschutz besitzen.

This work deals with the sensor application of polythiophenes, which belong to the group of the conducting polymers. The first part focuses on sensor application of poly(3,4-ethylenedioxythiophene) (PEDOT) for ion detection in aqueous electrolytes. The advanced electrochemical quartz crystal microbalance was used for investigating the electrochemical polymerisation and the redox cycling behaviour of the polymer films deposited on the liquid facing electrode of the quartz. This method is based on impedance analysis of a piezoelectric quartz crystal. The deposited polymer mass and surface roughness parameters were estimated from the electrical impedance shift of the quartz during the polymerisation using a new calculation procedure for rough and viscoelastic films. The PEDOT data were compared with results from the electrochemical polymerisation of 2,2?-bithiophene to demonstrate the influence of the substituent on morphology and electrochemical properties in organic electrolytes. With regard to electrogravimetric sensor applications the ion exchange of the polymer in aqueous electrolytes (LiClO4, NaClO4, NaNO3, and sodium toluenesulfonate) during redox cycling was investigated. From the mass/charge balance the apparent exchanged molar mass and the absolute exchanged mass of ions were calculated. The mass balance indicated a transfer of anions and solvent during oxidation. No remarkable cation exchange in the reduction scan was observed. For all investigated electrolytes the calculated exchanged molar mass can be explained with a reversible replacement of solvent by anions during oxidation. The molar solvent/anion ratio was roughly proportional to the sizes of the species. The second part of the work describes investigations on gas sensing properties of polythiophene films prepared by a new preparation method. This two-step procedure is based on electroless polymerisation of conducting polymers. In the first step the substrate is coated with an adhesion promoter and in a second step the chemical surface polymerisation of the monomer is performed. This deposition method was combined with new patterning techniques. The basis of this process is the patterned application of the adhesion promoter which was realised either by a photoresist lacquer mask or by micro contact printing of the adhesion promoter solution. These methods provide patterning down to submicrometer scale. The sensing properties of the polythiophene films were demonstrated with chemiresistors for the redox active gases NO2 and NH3. The reaction kinetics were investigated depending on humidity and temperature. / Die Arbeit befasst sich mit der Untersuchung von Polythiophenen, einer Gruppe der intrinsisch leitfähigen Polymere, für die Anwendung als sensitive Filme in chemischen Sensoren. Ziel war es dabei, ausgewählte Aspekte des Sensoreinsatzes dieser Polymere zu beleuchten, um Wege zu einer verbesserten Sensorcharakteristik solcher Systeme aufzuzeigen. Der erste Teil der Ergebnisse konzentriert sich auf den Einsatz von Poly(3,4-ethylendioxythiophen) in Sensoren für die Bestimmung von Ionenkonzentrationen in wässrigen Medien. Die elektrochemische Polymerisation auf Schwingquarzen und der potentialinduzierte Ionenaustausch an solchen Polymerfilmen wurden mit Hilfe der elektrochemischen Quarzmikrowaage charakterisiert. Diese beruht auf der Impedanzanalyse von Schwingquarzen in der Nähe ihrer Resonanzfrequenz, was neben der Erfassung der Änderung der Resonanzfrequenz der Quarze auch die Untersuchung des Dämpfungsverhaltens und somit eine halbquantitative Analyse der mechanischen Eigenschaften des Polymerfilmes ermöglicht. Aus den Daten Impedanzanalyse während der Polymerisation wurden mit einem neuen Berechnungsmodells, das viskoelastische und rauhigkeitsinduzierte Einflüsse berücksichtigt, die Polymermasse und vertikale und laterale Rauhigkeitsparameter bestimmt. Der Einfluss des Substituenten auf die Morphologie und das elektrochemische Verhalten in organischen Elektrolyten ist durch Vergleichsuntersuchungen an Poly(2,2?-bithiophen) illustriert. Die Sensormessungen erfolgten in wässrigen Modellelektrolyten mit unterschiedlich großen Anionen (LiClO4, NaClO4, NaNO3, Natriumtoluolsulfonat). Für die potentialabhängige Ionenaustauschreaktion konnte ein Einbau von Anionen bei der Oxidation des Polymers, der mit einem Ausstoß von Lösungsmittel verbunden war, nachgewiesen werden. Bei Reduktion des Polymers war der umgekehrte Vorgang zu beobachten. Kationen waren nicht nachweislich an den Austauschprozessen beteiligt. Als Sensorsignal wurde aus der bei Einbau der Ionen geflossenen Ladung und der reaktionsbedingten Masseänderung die ausgetauschte molare Masse und die inkorporierte Ionenmenge bestimmt. Die ausgetauschte molare Masse ergab für die unterschiedlichen Ionenspezies typische Werte, was eine Identifizierung der jeweiligen Analyten erlaubt. Die berechnete Analytmenge belegte eine erhöhte Empfindlichkeit für das in der Polymerisation verwendete Anion (Perchlorat) und eine geringe Empfindlichkeit für große Anionen (Toluolsulfonat) Für dünne, weniger poröse Filme war das Austauschverhältnis von Anion und Lösungsmittel annähernd proportional zu den Molekülgrößen der beteiligten Spezies. Ein zweiter Schwerpunkt der Arbeit war die Weiterentwicklung eines Verfahrens zur oxidativ?chemischen Abscheidung von Polythiophenfilmen unter Nutzung haftvermittelnder Substanzen. Dafür wurde die Filmqualität experimentell optimiert und Methoden zur strukturierten Abscheidung entwickelt. Zur Strukturierung der Polymerfilme wurden Methoden zur lokalen Aufbringung des Haftvermittlers auf Basis einer Maskierung des Substrates mit photostrukturierbaren Lackmasken bzw. auf Basis des Mikrokontaktdruckes der Haftvermittlerlösung entwickelt. Mit der Maskentechnik konnten Strukturen im Submikrometerbereich, mit dem Mikrokontaktdruck im Mikrometerbereich, erzielt werden. Der Nachweis der Sensitivität der chemisch polymerisierten Polythiophenfilme wurde für redoxaktive Gase mit Hilfe von Leitfähigkeitssensoren erbracht, und die Reaktionskinetik in Abhängigkeit von Feuchte und Temperatur untersucht.

<p>Synthetic carbohydrate carrying polymers have gained substantial attention recently due to their biocompatibility and their wide range of applications such as targeted drug delivery systems, gene therapy and cell-specific biomedical materials. The overall objective of this research is to develop novel carbohydrate bearing polymers through modification of polyvinylamine (PVAm) backbone with galactose groups and to discover potential applications for this new category of glycopolymers.</p> <p>PVAm-g-galactose (PVAm-GAL) with various molecular weights and grafting extents were prepared and characterized by nuclear magnetic resonance (NMR) and potentiometric and conductometric titration. Bonding of PVAm-GAL with phenylboronic acid modified PVAm (PVAm-PBA) and phenylboronate modified surfaces were studied on a quartz crystal microbalance with dissipation (QCM-D). Multilayer assembly of alternating layers of PVAm-GAL and PVA-PBA was formed on the silica sensor.</p> <p>Interaction of PVAm-GAL with RCA₁₂₀ lectin, a galactose specific protein, was studied on a silica sensor using QCM-D. Galactose binding proteins are overexpressed in hepatocyte and have been widely exploited for targeting the liver tissue with the help of galactosylated polymeric carriers. RCA₁₂₀lectin shows spontaneous adsorption on galactose rich surfaces obtained by the adsorption of PVAm-GAL on silica sensors. Association constant of the interaction was calculated . Effect of pretreatment with bovine serum albumin (BSA) was also examined.</p> <p>Cationic polymers can form polyelectrolyte complexes (PECs) with negatively charged DNA, resulting in formation of nano-sized complexes for gene delivery purposes. PECs based on PVAm-GAL and different DNA samples were prepared and their physicochemical properties were investigated using dynamic light scattering (DLS) and electrophoretic mobility measurements. Furthermore, PVAm-GAL was studied as coating for Ca-alginate beads which are widely used for cell encapsulation purposes. PVAm-GAL can strengthen the capsule’s surface and increase the physicochemical stability of the beads against chemical degradations. PVAm-GAL coated alginate beads successfully survived treatment with sodium citrate and high ionic strength solutions.</p> / Master of Applied Science (MASc)

With the aim of developing a deeper understanding of particle behaviour within nano-hybrid materials, this thesis investigates the particle-particle and particle-polymer interactions that influence and control cellulose nanocrystal dispersion in aqueous and non-aqueous environments. / Cellulose nanocrystals (CNCs) are rigid rod-shaped nanoparticles derived from bio-based resources and are considered an emerging nanomaterial based on their commercial availability and favourable properties. CNCs have great potential as reinforcing agents in hybrid materials and composite applications if they are well-dispersed. Whereas colloidal stability is effectively described by established theories, dispersing nanoparticles from an aggregated state, and their interaction with polymers can be difficult to predict and control. Herein, the particle-particle and particle-polymer interactions that govern CNC dispersibility in aqueous and non-aqueous environments are examined. The surface chemistry, morphology and colloidal/thermal stability of CNCs from North American industrial producers were extensively characterized such that particle interactions could be reproducibly measured from a known starting material. Industrially produced CNCs compared well to those produced at the bench-scale, implying that laboratory results should be translatable to the development of new CNC-based products. To examine particle-particle interactions within dry CNC aggregates, a surface plasmon resonance-based platform was developed to monitor CNC film swelling in a range of solvents and salt solutions. Water was observed to interrupt particle-particle hydrogen bonding most effectively, however film stability, and ultimately particle aggregation, was maintained by strong van der Waals interactions. Moreover, particle spacing and overall film thickness was found to be independent of the CNC surface chemistries and surface charge densities examined, yet the rate of film swelling scaled with the ionic strength of the surrounding media. Polyethylene glycol (PEG) was used as a model, non-ionic, water-soluble polymer to investigate polymer adsorption to CNC surfaces in water. PEG did not adsorb to CNCs despite the abundance of hydroxyl groups, which is in direct contrast to silica particles that are well known to hydrogen bond with PEG. Combining the knowledge of both particle-particle and particle-polymer interactions, PEG nanocomposites reinforced with CNCs and silica were compared and particle dispersibility was related to composite performance. Although PEG does not adsorb to CNCs in aqueous environments, polymer adsorption does occur in dry polymer nanocomposites leading to good dispersibility and improved mechanical properties. Overall, the work presented here yields new insight into the forces that govern CNC dispersion and provides a foundation from which a variety of new CNC-based products can be developed. / Thesis / Doctor of Philosophy (PhD) / Using particles derived from renewable resources to reinforce plastics and other materials has the potential to make products lighter, stronger and more environmentally friendly. However, to make these products we need to understand how to control and distribute particles uniformly throughout hybrid/composite materials. This work uses particles extracted from trees and cotton, known as cellulose nanocrystals, to reveal which factors govern particle dispersion in reinforced composite materials. To do so, first the properties and performance of commercially available cellulose nanocrystals were extensively analyzed and compared to form the basis from which interactions can be understood. Next, particle films were measured in water, organic solvents and salt solutions to better understand how aggregated cellulose nanocrystals can be separated within composite materials. The interactions between water-soluble polymers and cellulose nanocrystals were then investigated to reveal how polymer adsorption impacts particle dispersibility. Finally reinforced polymer composites were prepared with uniformly distributed cellulose nanocrystals and the crystallization and mechanical properties were investigated. By developing a deeper understanding of the factors that control cellulose nanocrystal dispersion we can learn how to make a variety of new and improved environmentally conscious products.

Natural polymers from renewable resources have attracted increasing interest as candidates for renewable energy and functional materials. In this work, the interactions between natural polymer thin films and biomacromolecules were studied via surface analysis techniques, such as a quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance (SPR) and atomic force microscopy (AFM). Chitinase activity on regenerated chitin (RChitin) films was studied by QCM-D and AFM. The optimal temperature and pH for chitinase activity on surfaces determined by QCM-D and AFM were consistent with bulk solution studies in the literature. Results from QCM-D also indicated that chitinase showed higher activity on fully acetylated chitin than highly deacetylated chitosan. Nanocrystalline chitin (Chitin NC) thin films were prepared by spincoating a nanocrystalline chitin colloidal suspension onto solid surfaces. Solvent exchange experiments via QCM-D with H2O/D2O revealed that Chitin NC films had more water than RChitin films of similar thickness. Results from QCM-D demonstrated that Chitin NC films had high bovine serum albumin loading capacity, and chitinase not only degraded, but also caused swelling of the chitin nanocrystals. Adsorption of human serum albumin (HSA) and fibrinogen (HFN) onto bare gold, regenerated cellulose (RC) and RChitin thin films was studied by SPR and QCM-D. Studies by SPR indicated that HSA and HFN formed close-packed monolayers on gold surfaces and sub-monolayers on polysaccharide surfaces, and the adsorption affinity of HSA for polysaccharide surfaces was greater than that of HFN. Results from QCM-D and SPR showed that the protein layers on polysaccharide surfaces had more associated water than proteins on gold surfaces. The dehydrogenative polymerization of monolignols catalyzed by physically immobilized horseradish peroxidase was investigated using QCM-D and AFM. Results from QCM-D and AFM showed that coniferyl and p-coumaryl alcohol underwent polymerization directly, whereas sinapyl alcohol required the addition of a nucleophile for polymerization. Studies by QCM-D and AFM also indicated that the surface-initiated polymerization was greatly affected by the support surface, monolignol concentration, hydrogen peroxide concentration and temperature. Thin films of dehydrogenative polymer (DHP), kraft (KL), organosolv (OL) and milled wood (MWL) lignins were used to study the enzymatic degradation of lignin mediated by lignin peroxidase (LiP) and manganese peroxidase (MnP). Results from QCM-D showed that the initial rates for degradation catalyzed by LiP increased in the order: KL < OL < MWL < guaiacyl DHP (G-DHP) < p-hydroxyphenyl DHP (H-DHP). In contrast, manganese peroxidase only degraded DHP films with a faster initial rate for G-DHP than H-DHP. Adsorption of hemicelluloses onto KL, OL and MWL thin films was studied by QCM-D and SPR. Results from QCM-D showed that hemicelluloses with different structures displayed very different adsorption behavior. Adsorption isotherms from QCM-D and SPR indicated that xyloglucan possessed stronger affinity for KL and OL films than MWL films. Data from QCM-D and SPR revealed that xyloglucan formed less hydrated layers on lignin surfaces compared to RC surfaces, and the adsorbed xyloglucan layers on different lignin films had similar percentages of coupled water. / Ph. D.

Tesis por compendio / [EN] Different electronic interfaces have been proposed to measure major parameters for the characterization of quartz crystal microbalance (QCM) during the last two decades. The measurement of the adequate parameters of the sensor for a specific application is very important, since an error in this measure can lead to an error in the interpretation of the results. The requirements of the system of characterization depend on the application. In this thesis we propose two characterization systems for two types of applications that involve the majority of sensor applications: 1) Characterization of materials under variable damping conditions and 2) Detection of substances with high measurement resolution. The proposed systems seek to solve the problems detected in the systems currently in use. For applications in which the sensor damping varies during the experiment, we propose a system based on a new configuration of the technique of automatic capacitance compensation (ACC). This new configuration provides the measure of the series resonance frequency, the motional resistance and the parallel capacitance of the sensor. Moreover, it allows an easy calibration of the system that improves the precision in the measurement. We show the experimental results for 9 and 10 MHz crystals in fluid media, with different capacitances in parallel, showing the effectiveness in the capacitance compensation. The system presents some deviation in frequency with respect to the series resonance frequency, as measured with an impedance analyser. These deviations are due to the non-ideal, specific behaviour of some of the components of the circuit. A new circuit is proposed as a possible solution to this problem. For high-resolution applications we propose an integrated platform to characterize high-frequency acoustic sensors. The proposed system is based on a new concept in which the sensor is interrogated by means of a very stable, low-noise external source at a constant frequency, while the changes provoked by the charge in the phase of the sensor are monitored. The use of high-frequency sensors enhances the sensitivity of the measure, whereas the design characterization system reduces the noise in the measurement. The result is an improvement in the limit of detection (LOD). This way, we achieve one of the challenges in the acoustic high-frequency devices. The validation of the platform is performed by means of an immunosensor based in high fundamental frequency QCM crystals (HFF-QCM) for the detection of two pesticides: carbaryl and thiabendazole. The results obtained for carbaryl are compared to the results obtained by another high-frequency acoustic technology based in Love sensors, with the optical technique based in surface plasmonic resonance and with the gold standard technique Enzyme Linked Immunoassay (ELISA). The LOD obtained with the acoustic sensors HFF-QCM and Love is similar to the one obtained with ELISA and improves by one order of magnitude the LOD obtained with SPR. The conceptual ease of the proposed system, its low cost and the possibility of miniaturization of the quartz resonator, allows the characterization of multiple sensors integrated in an array configuration, which will allow in the future to achieve the challenge of multianalyte detection for applications of High-Throughput Screening (HTS). / [ES] Durante las dos últimas décadas se han propuesto diferentes interfaces electrónicos para medir los parámetros más importantes de caracterización de los cristales de microbalanza de cuarzo (QCM). La medida de los parámetros adecuados del sensor para una aplicación específica es muy importante, ya que un error en la medida de dichos parámetros puede resultar en un error en la interpretación de los resultados. Los requerimientos del sistema de caracterización dependen de la aplicación. En esta tesis se proponen dos sistemas de caracterización para dos ámbitos de aplicación que comprenden la mayoría de las aplicaciones con sensores QCM: 1) Caracterización de materiales bajo condiciones de amortiguamiento variable y 2) detección de sustancias con alta resolución de medida. Los sistemas propuestos tratan de resolver la problemática detectada en los ya existentes. Para aplicaciones en las que el amortiguamiento del sensor varía durante el experimento, se propone un sistema basado en una nueva configuración de la técnica de compensación automática de capacidad (ACC). La nueva configuración proporciona la medida de la frecuencia de resonancia serie, la resistencia dinámica y la capacidad paralelo del sensor. Además, permite una fácil calibración del sistema que mejora la precisión en la medida. Se presentan resultados experimentales para cristales de 9 y 10MHz en medios fluidos, con diferentes capacidades en paralelo, demostrando la efectividad de la compensación de capacidad. El sistema presenta alguna desviación en frecuencia con respecto a la frecuencia resonancia serie, medida con un analizador de impedancias. Estas desviaciones son explicadas convenientemente, debidas al comportamiento no ideal específico de algunoscomponentes del circuito. Una nueva propuesta de circuito se presenta como posible solución a este problema. Para aplicaciones de alta resolución se propone una plataforma integrada para caracterizar sensores acústicos de alta frecuencia. El sistema propuesto se basa en un nuevo concepto en el que el sensor es interrogado, mediante una fuente externa muy estable y de muy bajo ruido, a una frecuencia constante mientras se monitorizan los cambios producidos por la carga en la fase del sensor. El uso de sensores de alta frecuencia aumenta la sensibilidad de la medida, por otro lado, el sistema de caracterización diseñado reduce el ruido en la misma. El resultado es una mejora del límite de detección (LOD). Se consigue con ello uno de los retos pendientes en los dispositivos acústicos de alta frecuencia. La validación de la plataforma desarrollada se realiza con una aplicación de un inmunosensor basado en cristales QCM de alta frecuencia fundamental (HFF-QCM) para la detección de dos pesticidas: carbaryl y tiabendazol. Los resultados obtenidos para el Carbaryl se comparan con los obtenidos con otra tecnología acústica de alta frecuencia basada en sensores Love, con la técnica óptica basada resonancia superficial de plasmones (SPR) y con la técnica de referencia Enzyme Linked Immuno Assay (ELISA). El LOD obtenido con los sensores acústicos HFFQCM y Love es similar al obtenido con las técnicas ELISA y mejora en un orden de magnitud al obtenido con SPR. La sencillez conceptual del sistema propuesto junto con su bajo coste, así como la capacidad de miniaturización del resonador de cuarzo hace posible la caracterización de múltiples sensores integrados en una configuración en array, esto permitirá en un futuro alcanzar el reto de la detección multianalito para aplicaciones High-Throughput Screening (HTS). / [CA] Durant les dues últimes dècades s'han proposat diferents interfases electrònics per a mesurar els paràmetres més importants de caracterització dels cristalls de microbalança de quars (QCM). La mesura dels paràmetres adequats del sensor per a una aplicació específica és molt important, perquè un error en la interpretació dels resultats pot resultar en un error en la interpretació dels resultats. Els requeriments del sistema de caracterització depenen de l'aplicació. En aquesta tesi, es proposen dos sistemes de caracterització per a dos àmbits d'aplicació que comprenen la majoria de les aplicacions amb sensors QCM: 1) Caracterització de materials sota condicions d'amortiment variable i 2) detecció de substàncies amb alta resolució de mesura. Els sistemes proposats tracten de resoldre la problemàtica detectada en els ja existents. Per a aplicacions en les quals l'amortiment del sensor varia durant l'experiment, es proposa un sistema basat en una nova configuració de la tècnica de compensació automàtica de capacitat (ACC). La nova configuració proporciona la mesura de la freqüència de ressonància sèrie, la resistència dinàmica i la capacitat paral¿lel del sensor. A més, permet un calibratge fàcil del sistema que millora la precisió de la mesura. Es presenten els resultats experimentals per a cristalls de 9 i 10 MHz en mitjans fluids, amb diferents capacitats en paral¿lel, demostrant l'efectivitat de la compensació de capacitat. El sistema presenta alguna desviació en freqüència respecte a la freqüència ressonància sèrie, mesurada amb un analitzador d'impedàncies. Aquestes desviacions són explicades convenientment, degudes al comportament no ideal específic d'alguns components del circuit. Una nova proposta de circuit es presenta com a possible solució a aquest problema. Per a aplicacions d'alta resolució es proposa una plataforma integrada per a caracteritzar sensors acústics d'alta freqüència. El sistema proposat es basa en un nou concepte en el qual el sensor és interrogat mitjançant una font externa molt estable i de molt baix soroll, a una freqüència constant mentre es monitoritzen els canvis produïts per la càrrega en la fase del sensor. L'ús de sensors d'alta freqüència augmenta la sensibilitat de la mesura, per altra banda, el sistema de caracterització dissenyat redueix el soroll en la mateixa. El resultat és una millora en el límit de detecció (LOD). S'aconsegueix amb això un dels reptes pendents en els dispositius acústics d'alta freqüència. La validació de la plataforma desenvolupada es realitza amb una aplicació d'un immunosensor basat en cristalls QCM d'alta freqüència fonamental (HFF-QCM) per a la detecció de dos pesticides: carbaryl i tiabendazol. Els resultats obtinguts per al carbaryl es comparen amb els obtinguts amb altra tecnologia acústica d'alta freqüència basada en sensors Love, amb la tècnica òptica basada en ressonància superficial de plasmons (SPR) i amb la tècnica de referència Enzyme Linked Immuno Assay (ELISA). El LOD obtingut amb els sensors acústics HFF-QCM i Love és similar al obtingut amb les tècniques ELISA i millora en un ordre de magnitud el obtingut amb SPR. La senzillesa conceptual del sistema proposat junt amb el seu baix cost, així com la capacitat de miniaturització del ressonador de quars fa possible la caracterització de múltiples sensors integrats en una configuració en array, el que permetrà en un futur assolir el repte de la detecció multianalit per a aplicacions High-Throughput Screening (HTS). / García Narbón, JV. (2016). Improved characterization systems for quartz crystal microbalance sensors: parallel capacitance compensation for variable damping conditions and integrated platform for high frequency sensors in high resolution applications [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/63249 / Compendio

This thesis presents the development and redesign of a commercial electrochemical quartz crystal microbalance with dissipation (E–QCM–D). This was used to study factors affecting the efficiency of the four electron reduction catalysed by the fuel cell enzyme bilirubin oxidase from Myrothecium verrucaria immobilised on thiol modified gold surfaces. Within this thesis, the E–QCM–D was used to show that application of a constant potential to bilirubin oxidase adsorbed to thiol-modified gold surfaces causes activity loss that can be attributed to a change in structural arrangement. Varying the load by potential cycling distorts the enzyme by inducing rapid mass loss and denaturation. Attaching the enzyme covalently reduces the mass loss caused by potential cycling but does not mitigate activity loss. Covalent attachment also changes the orientation of the surface bound enzyme as verified by the position of the catalytic wave (related to the overpotential for catalysis) and reactive labelling followed by mass spectrometry analysis. The E–QCM–D was used to show how electrostatic interactions affect enzyme conformation where high pH causes a reduction in both mass loading at the electrode and a reduction in activity. At pH lower than the enzyme isoelectric point, there is a build up of multilayers in a clustered adsorption. When enzyme adsorbs to hydrophobic surfaces there is a rapid denaturation which completely inactivates the enzyme. Changing the surface chemistry from carboxyl groups to hydroxyl and acetamido groups shows that catalysis is shifted to more negative potentials as a result of an enzyme misorientation. Further to this, increasing the chain length of the thiol modifier indicates that an increased distance between surface and enzyme reduces activity, enzyme loading and results in a conformational rearrangement that permits electron transfer over longer distances.

The Gram-negative bacterium Pseudomonas aeruginosa is a life-threatening nosocomial pathogen due to its generally low susceptibility toward antibiotics. Furthermore, many strains have acquired resistance mechanisms requiring new antimicrobials with novel mechanisms to enhance treatment options. Proline-rich antimicrobial peptides, such as the apidaecin analog Api137, are highly efficient against various Enterobacteriaceae infections in mice, but less active against P. aeruginosa in vitro. Here, we extended our recent work by optimizing lead peptides Api755 (gu-OIORPVYOPRPRPPHPRL-OH; gu = N,N,N′,N′-tetramethylguanidino, O = L-ornithine) and Api760 (gu-OWORPVYOPRPRPPHPRL-OH) by incorporation of Ile-Orn- and Trp-Orn-motifs, respectively. Api795 (gu-O(IO)2RPVYOPRPRPPHPRL-OH) and Api794 (gu-O(WO)3RPVYOPRPRPPHPRL-OH) were highly active against P. aeruginosa with minimal inhibitory concentrations of 8–16 and 8–32 μg/mL against Escherichia coli and Klebsiella pneumoniae. Assessed using a quartz crystal microbalance, these peptides inserted into a membrane layer and the surface activity increased gradually from Api137, over Api795, to Api794. This mode of action was confirmed by transmission electron microscopy indicating some membrane damage only at the high peptide concentrations. Api794 and Api795 were highly stable against serum proteases (half-life times >5 h) and non-hemolytic to human erythrocytes at peptide concentrations of 0.6 g/L. At this concentration, Api795 reduced the cell viability of HeLa cells only slightly, whereas the IC50 of Api794 was 0.23 ± 0.09 g/L. Confocal fluorescence microscopy revealed no colocalization of 5(6)-carboxyfluorescein-labeled Api794 or Api795 with the mitochondria, excluding interactions with the mitochondrial membrane. Interestingly, Api795 was localized in endosomes, whereas Api794 was present in endosomes and the cytosol. This was verified using flow cytometry showing a 50% higher uptake of Api794 in HeLa cells compared with Api795. The uptake was reduced for both peptides by 50 and 80%, respectively, after inhibiting endocytotic uptake with dynasore. In summary, Api794 and Api795 were highly active against P. aeruginosa in vitro. Both peptides passed across the bacterial membrane efficiently, most likely then disturbing the ribosome assembly, and resulting in further intracellular damage. Api795 with its IOIO-motif, which was particularly active and only slightly toxic in vitro, appears to represent a promising third generation lead compound for the development of novel antibiotics against P. aeruginosa.