Bilirrubina oxidase de Myrothecium verrucaria é uma multicobre oxidase capaz de reduzir O2 pela oxidação de fenóis, aminas aromáticas e polipirróis. Eletroquimicamente, essa reação de redução ocorre pela transferência de elétrons entre a enzima e um eletrodo. Nesta tese, foi investigada a eficiência da enzima como agente redutor de O2 na superfície de eletrodos modificados pela função orgânica naftil-2-carboxilato por acoplamento de diazônio. Essa modificação na superfície do eletrodo aumenta em até quatro vezes a atividade do filme catalítico em relação à obtida por eletrodos em que a adsorção da enzima foi feita de forma convencional, sem a modificação. Foram estudados os efeitos da temperatura sobre a atividade da enzima para a redução de O2, sendo observado um aumento linear da atividade do eletrodo com o aumento da temperatura até 30 °C, de tal forma que temperaturas mais altas proporcionaram o aumento da inativação natural das moléculas de enzima. Esse efeito de inativação foi confirmado pela diminuição da atividade com o tempo na presença de O2, por cronoamperometria, sendo a atividade interrompida pela inserção de argônio e retomada do mesmo ponto pela reinserção de O2, descartando a idéia da queda de corrente proveniente da dessorção de enzima. Foi estudado também o efeito do pH na máxima atividade da bilirrubina oxidase, conduzidos entre pH 5,0 e 8,0, e verificando-se que a máxima atividade da enzima foi obtida entre pH 5,5 e 6,0 e, além disso, verificou-se que a corrente catalítica em baixos valores de pH aumenta diretamente com o aumento do sobrepotencial aplicado. Porém, em altos valores de pH, a curva de redução toma a forma sigmoidal e passa a ser independente do sobrepotencial aplicado, sendo a reação governada por etapas químicas de transferência de prótons. O uso de eletrodos de disco rotatório possibilitou resolver parâmetros de Michaelis-Menten para a cinética do filme catalítico de forma mais precisa (a resposta de corrente é menos dependente do transporte de massa de reagentes) e esses dados foram obtidos dentro de um intervalo de pH importante para aplicações práticas. O sobrepotencial da reação de redução de O2 catalisada por bilirrubina oxidase foi comparado com o sobrepotencial obtido para a mesma reação catalisada por Platina eletrodepositada sobre a superfície de grafite pirolítico, onde foi observado um sobrepotencial de 140 mV para a catálise enzimática, demasiado menor que o valor de 415 mV obtidos para a Platina, sob as mesmas condições experimentais, em pH neutro. A metodologia proposta para a construção de um cátodo para aplicação em células a combustível enzimáticas e os subsequentes estudos possibilitaram uma investigação minuciosa para caracterizar a enzima bilirrubina oxidase como talvez o catalisador mais eficiente na redução eletroquímica de oxigênio molecular em células a combustível até o momento. / Bilirubin oxidase from Myrothecium verrucaria is a multicopper oxidase reducing O2 at the expenses of phenols, aromatic amines and polypyrrols oxidation. Electrochemically, this reduction reaction undergoes through the electron transfer between enzyme and electrode. In this thesis, the enzyme was investigated as an efficient O2 reducing agent on electrode surfaces modified by naphthil-2-carboxylate functionalities through diazonium coupling. This modification of the electrode surface increases the activity of the catalytic film up to four times comparing to that obtained by electrodes in which the enzyme molecules were adsorbed conventionally, without modification. It was studied the effect of temperature on O2 reduction, in which catalysis increased linearly with temperature up to 30 °C, and higher temperatures increased the natural enzyme inactivation. This inactivation was confirmed by the activity drop off with time in the presence of O2, by chronoamperometry, ceased out when argon was inserted into the cell and re-established from the same point when argon was purged out by insertion of O2. These results cast aside the idea of activity drop off caused by enzyme desorption. It was also investigated the pH effect on the maximum activity of bilirubin oxidase, carried out between pH 5.0 and 8.0, being the highest activity obtained at pH 5.5-6.0. Furthermore, it was observed that the catalytic current directly increases with applied overpotential, at low pH values, and the reduction wave shape becomes sigmoidal and independent on applied overpotential at high pH values. The reaction is then governed by chemical steps, as the proton transfer. The use of rotating-disc electrodes favored solving the Michaelis-Menten kinetics for the catalytic film in a much greater accuracy (the current response is much less dependent on reagent mass transport) and these data were obtained for pH interval important for practical applications. The overpotential for the O2 reduction reaction catalyzed by bilirubin oxidase was compared to the overpotential obtained by the same reaction catalyzed by Platinum electrodeposited onto a pyrolytic graphite electrode. An overpotential of only 140 mV was observed for the enzymatic catalysis, much lower compared to the 415 mV obtained for the Platinum electrode, under the same experimental conditions, at neutral pH. The proposed method for constructing a cathode for enzymatic fuel cell application and subsequent investigation described allowed an in-depth study of bilirubin oxidase characterization as perhaps the most efficient catalysts for the electrochemical reduction of molecular oxygen in fuel cells to date.

As biocélulas a combustível enzimáticas (BFCs) são dispositivos eletroquímicos que convertem energia química em energia elétrica, utilizando enzimas como biocatalisadores. Quando miniaturizada, uma BFC pode ser implantada em animais vertebrados e invertebrados, vislumbrando-se sua utilização na produção de energia elétrica para alimentar microdispositivos biomédicos e microssensores em pequenos insetos. No entanto, ainda é um desafio obter BFCs implantáveis e miniaturizadas, com uma potência suficiente (dezenas de microwatts) para alimentar microcircuitos eletrônicos de maneira estável e em longo prazo. Diante do exposto, esta tese de doutorado apresenta um estudo das propriedades eletroquímicas de eletrodos enzimáticos, visando a aplicação em BFCs de glicose/O2 miniaturizadas e implantáveis. Para isso, utilizaram-se fibras flexíveis de carbono (FCFs) modificadas com as enzimas bilirrubina oxidase (BOx) no cátodo e glicose desidrogenase (GDh) NAD-dependente no ânodo, a fim de se obter a redução de O2 e a oxidação de glicose, respectivamente. Os resultados obtidos mostram que FCFs previamente submetidas a um tratamento químico de oxidação com permanganato de potássio e com posterior eletrodepolimerização do mediador vermelho neutro produzem bioânodos estáveis e robustos. Estes eletrodos, combinados com biocátodos compostos por FCFs na ausência de mediadores redox, foram utilizados em BFCs miniaturizadas, que foram implantadas em formigas da espécie Atta sexdens rubrupilosa. A potência máxima da BFC operando in vivo foi 13,5 ± 3,8 µW cm-2 em 190 ± 58,9 mV, com corrente máxima de 143 ± 40,2 µA cm-2 e a voltagem de circuito aberto de 260 ± 99,6 mV. Acredita-se que estes valores ainda possam ser otimizados e este trabalho contribui para mostrar que a flexibilidade das FFC, a presença de um mediador de elétrons polimérico no ânodo, o uso do tratamento químico de oxidação com permanganato de potássio das fibras e a miniaturização dos eletrodos são elementos importantes, e que podem ser considerados no desenvolvimento de biocélulas a combustível implantáveis. / Enzymatic biofuel cells (BFCs) are electrochemical devices that convert chemical energy into electrical energy using enzymes as biocatalysts. When miniaturized, BFCs can be implanted in vertebrate and invertebrate animals and, their use to produce electrical energy to feed biomedical microdevices and micro-sensors in small insects can be observed. However, it is still challenging to obtain implantable and miniaturized BFCs, with sufficient power (tens of microwatts) to power electronic microcircuits in a stable and long-term manner. In view of the above, this PhD thesis presents a study of the electrochemical properties of enzymatic electrodes, aiming to use them in miniaturized and implantable glucose/O2 BFCs. In order to obtain a reduction in O2 and oxidation of glucose, flexible carbon fibers (FCFs) modified with bilirubin oxidase (BOx) enzymes in the cathode and glucose dehydrogenase (GDh) at the anode, respectively, were used. The results show that FCFs previously submitted to a chemical treatment of oxidation with potassium permanganate and, subsequently, electropolymerization of the neutral red mediator produce stable and robust bioanodes. These electrodes, combined with biocathodes consisting of FCFs in the absence of redox mediators, were used in miniaturized BFCs, which were implanted in Atta sexdens rubrupilosa ant species. The BFC maximum power source, operating in vivo, was 13.5 ± 3.8 μW cm-2 at 190 ± 58.9 mV, with a maximum current of 143 ± 40.2 μA cm-2 and the open circuit voltage was 260 ± 99.6 mV. Although these values can be optimized, this research shows that the flexibility of the FCF, the presence of a polymer electron mediator on the anode, using the chemical treatment of oxidation with potassium permanganate of the fibers and electrode miniaturization are important elements, which can be considered in the development of implantable biofuels.

Electron transfer phenomena in proteins represent one of the most common types of biochemical reactions. They play a central role in energy conversion pathways in living cells, and are crucial components in respiration and photosynthesis. These complex biochemical reaction cascades consist of a series of proteins and protein complexes that couple a charge transfer to different forms of chemical energy. The efficiency and sophisticated optimisation of signal transfer in these natural redox chains has inspired engineering of artificial architectures mimicking essential properties of their natural analogues. Implementation of direct electron transfer (DET) in protein assemblies was a breakthrough in bioelectronics, providing a simple and efficient way for coupling biological recognition events to a signal transducer. DET avoids the use of redox mediators, reducing potential interferences and side reactions, as well as being more compatible with in vivo conditions. However, only a few haem proteins, including the redox protein cytochrome c (cyt.c), and blue copper enzymes show efficient DET on different kinds of electrodes. Previous investigations with cyt.c have mainly focused on heterogeneous electron transfer of monolayers of this protein on gold. An important advance was the fabrication of cyt.c multilayers by electrostatic layer-by-layer self-assembly. The ease of fabrication, the stability, and the controllable permeability of polyelectrolyte multilayers have made them particularly attractive for electroanalytical applications. With cyt.c and sulfonated polyaniline it was for the first time possible that fully electro-active multilayers of the redox protein could be prepared. This approach was extended to design an analytical signal chain based on multilayers of cyt.c and xanthine oxidase (XOD). The system does not need an external mediator but relies on an in situ generation of a mediating radical and thus allows a signal transfer from hypoxanthine via the substrate converting enzyme and cyt.c to the electrode. Another kind of a signal chain is based on assembling proteins in complexes on electrodes in such a way that a direct protein-protein electron transfer becomes feasible. This design does not need a redox mediator in analogy to natural protein communication. For this purpose, cyt.c and the enzyme bilirubin oxidase (BOD, EC 1.3.3.5) are co-immobilized in a self-assembled polyelectrolyte multilayer on gold electrodes. Although these two proteins are not natural reaction partners, the protein architecture facilitates an electron transfer from the electrode via multiple protein layers to molecular oxygen resulting in a significant catalytic reduction current. Finally, we describe a novel strategy for multi-protein layer-by-layer self-assembly combining cyt.c with an enzyme sulfite oxidase (SOx) without use of any additional polymer. Electrostatic interactions between these two proteins with rather separated pI values during the assembly process from a low ionic strength buffer were found sufficient for the layer-by-layer deposition of the both biomolecules. It is anticipated that the concepts described in this work will stimulate further progress in multilayer design of even more complex biomimetic signal cascades taking advantage of direct communication between proteins. / Elektronentransferphänomene in Proteinen stellen den häufigsten Typ biochemischer Reaktionen dar. Sie spielen eine zentrale Rolle bei der Energieumwandlung in der Zelle und sind entscheidende Komponenten in der Atmung und Photosynthese. Diese komplexen Kaskaden biochemischer Reaktionen setzen sich aus einer Reihe von Proteinen und Proteinkomplexen zusammen, die den Energietransfer an verschiedene Formen chemischer Energie koppeln. Die große Effektivität und Selektivität des Signaltransfers in diesen natürlichen Redoxketten war Vorbild für die Entwicklung künstlicher Architekturen, die die wesentlichen Eigenschaften ihrer natürlichen Analoga nachahmen. Die Implementierung des direkten Elektronentransfers (DET) von Proteinen mit Elektroden war ein Durchbruch im Bereich der Bioelektronik. Sie lieferte einen einfachen und effizienten Weg für das Koppeln biologischer Erkennungsereignisse an einen Signalumwandler. Durch den DET können Redoxmediatoren vermieden und damit potentielle Grenzflächen und Nebenreaktionen reduziert werden. Ebenso wird damit die Kompatibilität für in vivo Bedingungen erhöht. Jedoch zeigen nur einige Hämproteine wie das Redoxprotein Cytochrom c (Cyt c) und blaue Kupferproteine einen effizienten DET auf verschiedenen Elektrodentypen. Bisherige Untersuchungen mit Cyt c konzentrierten sich hauptsächlich auf den heterogenen Elektronentransfer von Monoschichten dieses Proteins auf Gold. Ein wichtiger Fortschritt war die Herstellung von Cyt c Multischichten durch die elektrostatische Layer-by-Layer-Technik. Die einfache Herstellung, die Stabilität sowie die kontrollierbaren Permeationseigenschaften von Polyelektrolyt-Multischichten machte sie besonders attraktiv für elektroanalytische Anwendungen. So gelang es auch zum ersten Mal vollständig elektroaktive Multischichten aus Cyt c und Polyanilinsulfonsäure zu präparieren. Dieser Ansatz wurde hier erweitert, um eine analytische Signalkette auf der Basis von Multischichten aus Cyt c und Xanthinoxidase zu entwerfen. Das System bedarf keinen externen Mediator, es hängt jedoch von der in situ Generierung eines vermittelnden Radikals ab und erlaubt daher einen Signaltransfer von Hypoxanthin über ein substratumwandelndes Enzym und Cyt c zur Elektrode. Eine andere Art von Signalketten basiert auf der Assemblierung von Proteinen in Komplexen auf Elektroden in solcher Art und Weise, daß ein direkter Protein-Protein-Elektronentransfer möglich wird. Dieser Ansatz benötigt keinen Redoxmediator in Analogie zu Beispielen aus dem biologischen Signaltransfer. Zu diesem Zweck werden Cyt c und das Enzym Bilirubinoxidase mit einem selbst-assemblierenden Polyelektrolyten auf einer Goldelektrode koimmobilisiert. Obwohl diese zwei Proteine keine natürlichen Reaktionspartner sind, unterstützt die Protein-Architektur einen Elektronentransfer von der Elektrode über mehrere Proteinschichten zu molekularem Sauerstoff und ergibt einen signifikanten katalytischen Reduktionsstrom. Schließlich wird eine neue Strategie beschrieben für eine Selbstassemblierung von Proteinen ohne zusätzlichen Polyelektrolyten - am Beispiel der Kombination von Cyt c mit Sulfitoxidase. Es stellte sich heraus, daß die elektrostatische Wechselwirkung zwischen diesen zwei Proteinen mit ziemlich weit voneinander entfernt liegenden pI-Werten während des Assemblierungsprozesses durch einen Puffer mit geringer Ionenstärke ausreicht um die beiden Biomoleküle nach dem Layer-by-Layer-Prinzip auf einer Elektrode abzuscheiden. Es wird erwartet, daß das entwickelte Konzept von Multiprotein-Assemblaten auf Elektroden weitere Fortschritte bei dem Entwurf von Multischichten und sogar noch komplexeren biomimetischen Signalkaskaden anregen wird und dabei der Vorteil der direkten Kommunikation zwischen Proteinen genutzt wird.

As biocélulas a combustível enzimáticas (BFCs) são dispositivos eletroquímicos que convertem energia química em energia elétrica, utilizando enzimas como biocatalisadores. Quando miniaturizada, uma BFC pode ser implantada em animais vertebrados e invertebrados, vislumbrando-se sua utilização na produção de energia elétrica para alimentar microdispositivos biomédicos e microssensores em pequenos insetos. No entanto, ainda é um desafio obter BFCs implantáveis e miniaturizadas, com uma potência suficiente (dezenas de microwatts) para alimentar microcircuitos eletrônicos de maneira estável e em longo prazo. Diante do exposto, esta tese de doutorado apresenta um estudo das propriedades eletroquímicas de eletrodos enzimáticos, visando a aplicação em BFCs de glicose/O2 miniaturizadas e implantáveis. Para isso, utilizaram-se fibras flexíveis de carbono (FCFs) modificadas com as enzimas bilirrubina oxidase (BOx) no cátodo e glicose desidrogenase (GDh) NAD-dependente no ânodo, a fim de se obter a redução de O2 e a oxidação de glicose, respectivamente. Os resultados obtidos mostram que FCFs previamente submetidas a um tratamento químico de oxidação com permanganato de potássio e com posterior eletrodepolimerização do mediador vermelho neutro produzem bioânodos estáveis e robustos. Estes eletrodos, combinados com biocátodos compostos por FCFs na ausência de mediadores redox, foram utilizados em BFCs miniaturizadas, que foram implantadas em formigas da espécie Atta sexdens rubrupilosa. A potência máxima da BFC operando in vivo foi 13,5 ± 3,8 µW cm-2 em 190 ± 58,9 mV, com corrente máxima de 143 ± 40,2 µA cm-2 e a voltagem de circuito aberto de 260 ± 99,6 mV. Acredita-se que estes valores ainda possam ser otimizados e este trabalho contribui para mostrar que a flexibilidade das FFC, a presença de um mediador de elétrons polimérico no ânodo, o uso do tratamento químico de oxidação com permanganato de potássio das fibras e a miniaturização dos eletrodos são elementos importantes, e que podem ser considerados no desenvolvimento de biocélulas a combustível implantáveis. / Enzymatic biofuel cells (BFCs) are electrochemical devices that convert chemical energy into electrical energy using enzymes as biocatalysts. When miniaturized, BFCs can be implanted in vertebrate and invertebrate animals and, their use to produce electrical energy to feed biomedical microdevices and micro-sensors in small insects can be observed. However, it is still challenging to obtain implantable and miniaturized BFCs, with sufficient power (tens of microwatts) to power electronic microcircuits in a stable and long-term manner. In view of the above, this PhD thesis presents a study of the electrochemical properties of enzymatic electrodes, aiming to use them in miniaturized and implantable glucose/O2 BFCs. In order to obtain a reduction in O2 and oxidation of glucose, flexible carbon fibers (FCFs) modified with bilirubin oxidase (BOx) enzymes in the cathode and glucose dehydrogenase (GDh) at the anode, respectively, were used. The results show that FCFs previously submitted to a chemical treatment of oxidation with potassium permanganate and, subsequently, electropolymerization of the neutral red mediator produce stable and robust bioanodes. These electrodes, combined with biocathodes consisting of FCFs in the absence of redox mediators, were used in miniaturized BFCs, which were implanted in Atta sexdens rubrupilosa ant species. The BFC maximum power source, operating in vivo, was 13.5 ± 3.8 μW cm-2 at 190 ± 58.9 mV, with a maximum current of 143 ± 40.2 μA cm-2 and the open circuit voltage was 260 ± 99.6 mV. Although these values can be optimized, this research shows that the flexibility of the FCF, the presence of a polymer electron mediator on the anode, using the chemical treatment of oxidation with potassium permanganate of the fibers and electrode miniaturization are important elements, which can be considered in the development of implantable biofuels.

Bilirrubina oxidase de Myrothecium verrucaria é uma multicobre oxidase capaz de reduzir O2 pela oxidação de fenóis, aminas aromáticas e polipirróis. Eletroquimicamente, essa reação de redução ocorre pela transferência de elétrons entre a enzima e um eletrodo. Nesta tese, foi investigada a eficiência da enzima como agente redutor de O2 na superfície de eletrodos modificados pela função orgânica naftil-2-carboxilato por acoplamento de diazônio. Essa modificação na superfície do eletrodo aumenta em até quatro vezes a atividade do filme catalítico em relação à obtida por eletrodos em que a adsorção da enzima foi feita de forma convencional, sem a modificação. Foram estudados os efeitos da temperatura sobre a atividade da enzima para a redução de O2, sendo observado um aumento linear da atividade do eletrodo com o aumento da temperatura até 30 °C, de tal forma que temperaturas mais altas proporcionaram o aumento da inativação natural das moléculas de enzima. Esse efeito de inativação foi confirmado pela diminuição da atividade com o tempo na presença de O2, por cronoamperometria, sendo a atividade interrompida pela inserção de argônio e retomada do mesmo ponto pela reinserção de O2, descartando a idéia da queda de corrente proveniente da dessorção de enzima. Foi estudado também o efeito do pH na máxima atividade da bilirrubina oxidase, conduzidos entre pH 5,0 e 8,0, e verificando-se que a máxima atividade da enzima foi obtida entre pH 5,5 e 6,0 e, além disso, verificou-se que a corrente catalítica em baixos valores de pH aumenta diretamente com o aumento do sobrepotencial aplicado. Porém, em altos valores de pH, a curva de redução toma a forma sigmoidal e passa a ser independente do sobrepotencial aplicado, sendo a reação governada por etapas químicas de transferência de prótons. O uso de eletrodos de disco rotatório possibilitou resolver parâmetros de Michaelis-Menten para a cinética do filme catalítico de forma mais precisa (a resposta de corrente é menos dependente do transporte de massa de reagentes) e esses dados foram obtidos dentro de um intervalo de pH importante para aplicações práticas. O sobrepotencial da reação de redução de O2 catalisada por bilirrubina oxidase foi comparado com o sobrepotencial obtido para a mesma reação catalisada por Platina eletrodepositada sobre a superfície de grafite pirolítico, onde foi observado um sobrepotencial de 140 mV para a catálise enzimática, demasiado menor que o valor de 415 mV obtidos para a Platina, sob as mesmas condições experimentais, em pH neutro. A metodologia proposta para a construção de um cátodo para aplicação em células a combustível enzimáticas e os subsequentes estudos possibilitaram uma investigação minuciosa para caracterizar a enzima bilirrubina oxidase como talvez o catalisador mais eficiente na redução eletroquímica de oxigênio molecular em células a combustível até o momento. / Bilirubin oxidase from Myrothecium verrucaria is a multicopper oxidase reducing O2 at the expenses of phenols, aromatic amines and polypyrrols oxidation. Electrochemically, this reduction reaction undergoes through the electron transfer between enzyme and electrode. In this thesis, the enzyme was investigated as an efficient O2 reducing agent on electrode surfaces modified by naphthil-2-carboxylate functionalities through diazonium coupling. This modification of the electrode surface increases the activity of the catalytic film up to four times comparing to that obtained by electrodes in which the enzyme molecules were adsorbed conventionally, without modification. It was studied the effect of temperature on O2 reduction, in which catalysis increased linearly with temperature up to 30 °C, and higher temperatures increased the natural enzyme inactivation. This inactivation was confirmed by the activity drop off with time in the presence of O2, by chronoamperometry, ceased out when argon was inserted into the cell and re-established from the same point when argon was purged out by insertion of O2. These results cast aside the idea of activity drop off caused by enzyme desorption. It was also investigated the pH effect on the maximum activity of bilirubin oxidase, carried out between pH 5.0 and 8.0, being the highest activity obtained at pH 5.5-6.0. Furthermore, it was observed that the catalytic current directly increases with applied overpotential, at low pH values, and the reduction wave shape becomes sigmoidal and independent on applied overpotential at high pH values. The reaction is then governed by chemical steps, as the proton transfer. The use of rotating-disc electrodes favored solving the Michaelis-Menten kinetics for the catalytic film in a much greater accuracy (the current response is much less dependent on reagent mass transport) and these data were obtained for pH interval important for practical applications. The overpotential for the O2 reduction reaction catalyzed by bilirubin oxidase was compared to the overpotential obtained by the same reaction catalyzed by Platinum electrodeposited onto a pyrolytic graphite electrode. An overpotential of only 140 mV was observed for the enzymatic catalysis, much lower compared to the 415 mV obtained for the Platinum electrode, under the same experimental conditions, at neutral pH. The proposed method for constructing a cathode for enzymatic fuel cell application and subsequent investigation described allowed an in-depth study of bilirubin oxidase characterization as perhaps the most efficient catalysts for the electrochemical reduction of molecular oxygen in fuel cells to date.

Parmi les technologies basées sur H2 comme vecteur d’énergie, les biopiles à combustibles utilisant des enzymes comme biocatalyseurs spécifiques et efficaces au lieu des catalyseurs au platine apparaissent comme des alternatives émergentes. L’objectif de cette thèse est de comprendre les paramètres gouvernant l’immobilisation fonctionnelle sur des interfaces nanostructurées d'enzymes spécifiques de l’oxydation de H2 et de la réduction d’O2 en vue de désigner une biopile H2/O2 performante.Divers nanomatériaux sont caractérisés, nanoparticules d’or (AuNP) et nanotubes de carbone (CNT), présentant différentes tailles et chimie de surface, aptes à développer des ratios importants surface/volume, autorisant une augmentation du nombre de molécules enzymatiques incorporées et donc une augmentation des courants catalytiques. L’immobilisation des enzymes sur AuNP a permis de discriminer entre l’augmentation de surface ou un effet nano sur l’efficacité catalytique. L’étude intégrée sur CNT, avec les charges de l’interface électrochimique, les charges et moments dipolaires des enzymes considérées, a permis de démontrer que les interactions électrostatiques contrôlent le processus de transfert d’électrons. Cette étude montre que les bases moléculaires pour une immobilisation efficace des enzymes, obtenues sur monocouches est applicables aux réseaux 3D.La détermination des nanostructures optimales pour les réactions enzymatiques est étudiée pour un changement d’échelle. Ainsi des feutres de carbone sont fonctionnalisés avec les nanostructures adaptées, pour au final développer la première biopile H2/O2 capable d’alimenter un multicapteur et un système de communication sans fil. / Among the technologies based on H2 as an energy carrier, biofuel cells that use specific and effective enzymes as biocatalysts instead of platinum catalysts appear as emerging alternative. The objective of this thesis is to understand the parameters governing the functional immobilization of specific enzymes for H2 oxidation and O2 reduction reactions on nanostructured interfaces, aimed to design a performant H2 / O2 biofuel cell.Gold nanoparticles (AuNP) and carbon nanotubes (CNT) having different sizes and surface chemistry are characterized. These nanomaterials develop important ratios surface / volume ratio, allow an increment in the number of enzyme molecules immobilized and therefore an increase catalytic currents. The immobilization of enzymes on AuNP allowed the discrimination between the increase in surface area and a nanomaterial effect on catalytic efficiency. The study on CNT integrates the charge of the electrochemical interface, dipole moments and the surface charge of enzymes. It demonstrated that electrostatic interactions control the electron transfer process. This study shows that the molecular basis for effective immobilization of enzymes, obtained on monolayers is applicable to 3D networks.The determination of the best parameters for enzymatic reactions, allows the development of an optimized 3-D volumetric interface based on carbon felt. We finally design for the first time a H2/O2 biofuel cell able to generate enough electric power to feed a complete wireless communication device.

La puissance de la biopile enzymatique à glucose/oxygène est limitée par sa partiecathodique. Afin de contourner cette limitation, nous avons étudié les enzymescathodiques : les Bilirubine oxydases (BODs). Dans le but de mieux appréhender ces BODs, lemécanisme réactionnel, la nature de l’étape limitante et l’effet des sels ont alors été étudiés.Deux mécanismes différents sont retrouvés en fonction du mode de transfert des protons etdes électrons (4 fois 1H+/1e- ou 2 fois 2H+/2e-). De plus, nous avons démontré que l’étapelimitante est l’oxydation du substrat pour les trois substrats testés et que les sels agissent auniveau du cuivre T1. Les principales limitations des BODs sont leur stabilité à 37 °C ainsi queleur inhibition par le NaCl. Deux techniques ont alors été utilisées pour identifier des BODsplus résistantes. La première méthode est l’extraction de nouvelles enzymes à partird’organismes extremophiles. Elle a permis d’isoler la BOD d’Anaerophaga thermohalophilaqui possède une bonne résistance au NaCl mais une densité de courant faible. Dans unsecond temps, afin de reconstruire des séquences ancestrales, la phylogénie de la familledes Bacillus Bacterium a été effectuée. Cette technique a permis l’identification de troisBODs possédant des caractéristiques très intéressantes : la BOD de Bacillus nakamurai etdeux BODs ancestrales (Noeud 10 et Noeud 13). Par exemple, après une heure à 37°C et 140mM de NaCl, le Noeud 10 possède une meilleure densité de courant que la BOD de Bacilluspumilus, qui est l’enzyme utilisée comme base de la phylogénie. La seconde technique estdonc une méthode de choix permettant la découverte de nouvelles enzymes à la fois plusstables et plus résistantes que les enzymes actuelles. Elle ouvre de grandes perspectivespour l’utilisation des BODs comme enzymes cathodiques ou pour d’autres applicationsbiotechnologiques. Enfin, nous avons montré que l’immobilisation de la BOD de B. pumilusdans le matériau Si-(HIPE) permet la décoloration cyclique de colorants chimiques surplusieurs mois. / Power of glucose/oxygen enzymatic biofuel cell is limited by the cathodic part. In order to prevent this limitation, we studied cathodic enzymes: Bilirubin oxidases (BODs). For this purpose, the kinetic mechanism, rate-limiting step and salts effect were determined. Two different mechanisms are observed depending on the electron/proton transfer (4 times1H+/1e- or 2 times 2H+/2e-). We also demonstrated that the rate-limiting step is the substrate oxidation for the three substrates tested and salts act around the T1 copper. Main BODs limitations are their stability at 37°C and their inhibition by NaCl. Two methods were used toidentify the most resistant BODs. The first one was the identification of new enzymes from extremophile organisms. It allows to isolate BOD from Anaerophaga thermohalophila whichhas good NaCl resistance but low current density. In addition, in order to reconstructancestral sequences, phylogeny of Bacillus Bacterium family was performed. This methodidentified three BODs with interesting features: BOD from Bacillus nakamurai and twoancestral BODs (Noeud 10 and Noeud 13). For example, after one hour at 37°C and 140 mMNaCl, Noeud 10 has a better current density than the BOD from Bacillus pumilus, which is theenzyme used as basis for the phylogeny. This second method allowed the discovery of newenzymes that were both more stable and more resistant than actual enzymes. Thistechnique opens up valuable prospects for the use of BODs as cathodic enzymes or for otherbiotechnological applications. In the end, we demonstrated that BOD from B. pumilusimmobilization in Si-(HIPE) materials allows cyclic discoloration of chemical dyes duringseveral months.

Biocélulas a combustível (BFCs) são definidas como dispositivos bioeletroquímicos que utilizam componentes biológicos, como enzimas ou microrganismos, para converter energia química em energia elétrica. Neste estudo, reporta-se o desenvolvimento de um bioeletrodo composto por fibras flexíveis de carbono (FFC) modificadas com a enzima álcool desidrogenase (ADH), o qual foi utilizado juntamente com a levedura Saccharomyces cerevisiae , sendo enzima e microrganismos usados como biocatalisadores cooperativos para bioprodução e oxidação de etanol. A glicose é oxidada pelas células de levedura sob condições anaeróbias, e o etanol formado pela fermentação alcóolica é, em seguida, oxidado a acetaldeído pela enzima ADH. A oxidação de etanol pela ADH resulta ainda, na redução da molécula de nicotinamida adenina dinucleotídeo, NAD+ a NADH. Posteriormente, o NADH formado nessa reação é eletroquimicamente oxidado a NAD+ na superfície do bioeletrodo de FFC baseado em ADH (FFC-ADH). Avaliou-se a influência da temperatura e do pH na bioeletrocatálise de etanol pela ADH e a melhor resposta obtida foi em 40 ºC e pH 8,5. Além disso, obteve-se uma excelente correlação linear entre os valores de concentração de etanol e densidade de corrente, indicando que a resposta bioeletrocatalítica da ADH é diretamente proporcional à concentração de etanol produzido a partir da fermentação. O conceito de que microrganismos e enzimas podem trabalhar cooperativamente para produzir uma nova classe de bioeletrodos, foi introduzido nesse trabalho. Por fim, demonstrou-se, que o bioeletrodo cooperativo pode ser aplicado com sucesso em uma BFC, utilizando o biocátodo de difusão de gás contendo a enzima bilirrubina oxidase (BOx) imobilizada em sua superfície. / Biofuel cells (BFCs) are defined as bioelectrochemical devices that use biological components, such as enzymes or microorganisms, to convert chemical energy into electric energy. In this study, we report the development of a bioelectrode composed of flexible carbon fibers (FCF) modified with the enzyme alcohol dehydrogenase (ADH) together with Saccharomyces cerevisiae yeast, being enzyme and microorganisms used as cooperative biocatalysts for bioproduction and oxidation of ethanol. Glucose is oxidized by the yeast cells in anaerobic conditions, and ethanol is produced through alcoholic fermentation and then it is oxidized to acetaldehyde by the ADH enzyme. The ethanol oxidation by ADH also results in the reduction of the nicotinamide adenine dinucleotide molecule, NAD+ to NADH. Subsequently, the NADH produced in this reaction is electrochemically oxidized to NAD+ on the surface of the FCF bioelectrode based on ADH (FCF-ADH). The influence of temperature and pH on the bioelectrocatalysis of ethanol was evaluated and the best performance was found at 40 ºC and pH 8.5. Additionally, the results demonstrated an excellent linear correlation between the ethanol concentration and the current generated, which indicates that the bioelectrocatalytic response of ADH is directly proportional to concentration of ethanol produced from the fermentation. The present study has introduced the concept that microorganisms and enzymes can work cooperatively to produce a new class of bioelectrodes. Finally, it has been demonstrated that the cooperative bioelectrode can be applied successfully to BFC using a gas-diffusion biocathode containing the bilirubin oxidase enzyme (BOx) immobilized on its surface.

Dans la nature, la réduction du dioxygène est catalysée par des enzymes de la famille des oxydoréductases. A l’heure actuelle, ces protéines spécifiques et efficaces sont envisagés comme biocatalyseurs au sein de biopile enzymatique. Dans ce contexte, l’optimisation de l’orientation et de la connexion d’oxydases multi-cuivre (MCOs) pour la réduction d’O2 sur des matrices de nanotubes carbone (CNTs) fonctionnalisées a été étudiée. Dans un premier temps, le transfert électronique direct de la laccase est optimisé par la fonctionnalisation non covalente de CNTs par divers dérivés hydrophobes. La dynamique moléculaire ainsi que la modélisation électrochimique ont permis la rationalisation des performances des différentes biocathodes développées. Dans une seconde approche, la modification spécifique par des groupements pyrène de la surface de laccases modifiées par mutagénèse a également été envisagée. La fonctionnalisation supramoléculaire de CNTs par des feuillets de graphène fonctionnalisés d’une part, et par des nanoparticules d’or d’autre part, a également permis de favoriser la connexion de laccases. La seconde partie présente l’élaboration d’autres types de biocathodes basées sur la connexion directe de bilirubines oxydases. Plusieurs stratégies de fonctionnalisation covalente et non covalente de CNTs ont été envisagées. Les différentes biocathodes élaborées par l’assemblage supramoléculaire de MCOs et de matériaux nanostructurés délivrent des densités de courant de réduction du dioxygène de plusieurs mA cm-2. Ces nouvelles bioélectrodes combinées à une bioanode qui catalyse l’oxydation du glucose ont permis le développement de biopiles enzymatiques glucose/O2 délivrant des densités maximales de puissances allant de 250 µW cm-2 à 750 µW cm-2 selon les conditions expérimentales. Enfin une bioanode à base d’une hydrogénase hyperthermophile a été développée et associée à une biocathode à base de bilirubine oxydase pour former un nouveau design de biopile H2/O2. Au sein de ce dispositif, la biocathode à diffusion de gaz réduit directement l’oxygène provenant de l’air, ce qui permet de s’affranchir de l’utilisation d’une membrane séparatrice tout en protégeant l’hydrogénase de sa désactivation en présence d’oxygène. Cette nouvelle biopile délivre une densité maximale de puissance de 750 µW cm-2. / The reduction of oxygen is realized in nature by oxidoreductase enzymes. Currently, these highly specific and efficient proteins are considered as biocatalysts for the development of biofuel cells. In this context, optimizing the orientation and the connection of multicopper oxidase (MCOs) for the reduction of O2 on functionalized carbon nanotubes was studied. In the first part of this manuscript, direct electron transfer of laccase is assessed and optimized by the non-covalent functionalization of CNTs by various hydrophobic derivatives. Electrochemical modeling and molecular dynamics enabled the rationalization of the developed biocathodes efficiency. In a second approach, the specific modification by pyrene moieties of laccases surface modified by protein engineered has also been considered. Additionally, supramolecular functionalization of CNTs by modified graphene sheets and gold nanoparticles also helped to promote laccase connection. The second part presents the development of other types of biocathodes based on the direct connection of bilirubin oxidase. Several strategies of covalent and non-covalent CNTs functionalization have been considered. The different biocathodes developed by the supramolecular assembly of nanostructured materials and MCOs delivered current density of several mA cm-2 for oxygen reduction. These new bioelectrodes combined with a bioanode which catalyzes the glucose oxidation have enabled the development of glucose/O2 enzymatic biofuel cells; delivering maximum power densities from 250 µW cm-2 to 750 µW cm-2 depending on the experimental conditions. Finally a hyperthermophilic hydrogenase based bioanode was developed and associated with a bilirubin oxidase-based biocathode to form a new design of H2/O2 biofuel cell. Within this device, the gas diffusion biocathode directly reduces oxygen from the air, which eliminates the use of a separation membrane while protecting the hydrogenase from its deactivation in the presence oxygen. This new biofuel cell delivers a maximum power density of 750 µW cm-2.

Biocélulas a combustível (BFCs) são definidas como dispositivos bioeletroquímicos que utilizam componentes biológicos, como enzimas ou microrganismos, para converter energia química em energia elétrica. Neste estudo, reporta-se o desenvolvimento de um bioeletrodo composto por fibras flexíveis de carbono (FFC) modificadas com a enzima álcool desidrogenase (ADH), o qual foi utilizado juntamente com a levedura Saccharomyces cerevisiae , sendo enzima e microrganismos usados como biocatalisadores cooperativos para bioprodução e oxidação de etanol. A glicose é oxidada pelas células de levedura sob condições anaeróbias, e o etanol formado pela fermentação alcóolica é, em seguida, oxidado a acetaldeído pela enzima ADH. A oxidação de etanol pela ADH resulta ainda, na redução da molécula de nicotinamida adenina dinucleotídeo, NAD+ a NADH. Posteriormente, o NADH formado nessa reação é eletroquimicamente oxidado a NAD+ na superfície do bioeletrodo de FFC baseado em ADH (FFC-ADH). Avaliou-se a influência da temperatura e do pH na bioeletrocatálise de etanol pela ADH e a melhor resposta obtida foi em 40 ºC e pH 8,5. Além disso, obteve-se uma excelente correlação linear entre os valores de concentração de etanol e densidade de corrente, indicando que a resposta bioeletrocatalítica da ADH é diretamente proporcional à concentração de etanol produzido a partir da fermentação. O conceito de que microrganismos e enzimas podem trabalhar cooperativamente para produzir uma nova classe de bioeletrodos, foi introduzido nesse trabalho. Por fim, demonstrou-se, que o bioeletrodo cooperativo pode ser aplicado com sucesso em uma BFC, utilizando o biocátodo de difusão de gás contendo a enzima bilirrubina oxidase (BOx) imobilizada em sua superfície. / Biofuel cells (BFCs) are defined as bioelectrochemical devices that use biological components, such as enzymes or microorganisms, to convert chemical energy into electric energy. In this study, we report the development of a bioelectrode composed of flexible carbon fibers (FCF) modified with the enzyme alcohol dehydrogenase (ADH) together with Saccharomyces cerevisiae yeast, being enzyme and microorganisms used as cooperative biocatalysts for bioproduction and oxidation of ethanol. Glucose is oxidized by the yeast cells in anaerobic conditions, and ethanol is produced through alcoholic fermentation and then it is oxidized to acetaldehyde by the ADH enzyme. The ethanol oxidation by ADH also results in the reduction of the nicotinamide adenine dinucleotide molecule, NAD+ to NADH. Subsequently, the NADH produced in this reaction is electrochemically oxidized to NAD+ on the surface of the FCF bioelectrode based on ADH (FCF-ADH). The influence of temperature and pH on the bioelectrocatalysis of ethanol was evaluated and the best performance was found at 40 ºC and pH 8.5. Additionally, the results demonstrated an excellent linear correlation between the ethanol concentration and the current generated, which indicates that the bioelectrocatalytic response of ADH is directly proportional to concentration of ethanol produced from the fermentation. The present study has introduced the concept that microorganisms and enzymes can work cooperatively to produce a new class of bioelectrodes. Finally, it has been demonstrated that the cooperative bioelectrode can be applied successfully to BFC using a gas-diffusion biocathode containing the bilirubin oxidase enzyme (BOx) immobilized on its surface.