Organic bioelectronics develops electronic devices at the interface with living systems using organic electronic materials. These devices can identify various chemical species and regulate the operation of individual cells, tissues, or organs. A famous organic bioelectronic device is the organic electrochemical transistor (OECT), a highly versatile circuit component that has been used in applications spanning from biosensing to neuromorphic computing. OECTs can be operated in aqueous electrolytes and use organic mixed ionic-electronic conductors (OMIECs) in their channel (and sometimes as gate electrode coating) that can transport electronic and ionic charges, making them ideal for bridging biological systems and silicon-based electronic devices. Electron-transporting (n-type) OMIEC materials have received particular attention because high-performance n-type OECTs can be used to build inverters, sensors, and complementary amplifiers. However, electron transport in an aqueous and ambient environment under the application of electrical fields is a complex phenomenon that requires in situ investigation techniques. Understanding how films operate in such media can allow to construct novel sensors and eliminate the loss processes. This Ph.D. dissertation focuses on the impact of the environment, specifically oxygen, and light, on the performance of n-type OECTs and shows how to use this knowledge to develop OECT-based glucose sensors and photodetectors. Chapter 1 introduces the mixed charge transport phenomenon in conjugated polymers and how to use it in OECT operation. OECT fabrication and various designs are described, setting the ground for the sensors we will show in the following chapters. The experimental procedures used to evaluate the critical figures of merit of the materials and the transistor performance are described in detail. Chapter 2 introduces how OECTs can be used to transduce biochemical binding events. When employing the OECT platform for biochemical sensing, it is essential to differentiate between the faradaic, capacitive, and potentiometric contributions to the sensor response. Understanding the underlying mechanisms is critical for optimizing performance. This chapter explains these different sensing mechanisms with literature examples. Chapter 3 compiles all experimental details relevant to the investigations presented in Chapters 4 and 5. Chapter 4 investigates the working mechanism of a novel n-type OECT-based glucose sensor relying on an enzymatic reaction. This chapter shows the oxygen reaction reactions and the importance of monitoring contact potentials during device operation to understand how detection occurs. The work unveils the role of the oxygen sensitivity of the n-type material on the sensor operation and suggests paths to improve performance. Chapter 5 explores the interactions of light with n-type OMIECs and how to utilize them to build water-compatible phototransistors. The first part of the chapter involves a characterization of the light/matter interplay of an n-type film and a demonstration of how to use it to build a photoelectrochemical transistor. The second part of the chapter expands this work to other n-type materials and assesses their light sensitivity, building a relationship between material property and device performance. Since most detection events lead to a change in the surface of materials, techniques that monitor surface roughness and profile changes in situ can be useful. Chapter 6 describes an atomic force microscopy (AFM) setup that can be used to investigate binding events and electrochemical doping and de-doping dynamics of OMIEC films. This chapter is intended to assist researchers in developing in-operando AFM procedures studying OMIEC films.

Les microorganismes photosynthétiques suscitent un intérêt biotechnologique important pour la production de dihydrogène. La cyanobactérie Synechocystis sp. PCC 6803 est capable d'initier une photoproduction d'hydrogène catalysée par une hydrogénase [NiFe] bidirectionnelle qui se présente sous la forme d'un complexe pentamérique (HoxEFUYH). Toutefois l'inhibition de cette enzyme par l'oxygène émis par le photosystème II rend cette photoproduction transitoire et constitue un verrou majeur au développement de tels procédés. L'exploitation de ces organismes impose une meilleure compréhension des bases moléculaires associées à la sensibilité de l'hydrogénase envers l'oxygène ainsi que des composantes limitant son activité de production d'H2, ce qui implique la connaissance détaillée des jeux d'interactions avec ses partenaires physiologiques NAD(P)+/NAD(P)H.Diverses substitutions d'acides aminés potentiellement impliqués dans la sensibilité de l'enzyme à l'O2 et situés au cœur du site actif (Ileu64, Leu107, Leu112) de la sous-unité catalytique HoxH ont été réalisées. Les résultats in vitro et in vivo indiquent une sensibilité envers l'O2 moindre chez le mutant I64M, qui présente une diffusion limitée et un biais vers l'activité de production d'H2.L'étude des interactions de mutants de délétion des gènes diaphorase hoxE et hoxF avec les cofacteurs NAD(P) a montré que NAD+/NADH semblent être les partenaires privilégiés de l'hydrogénase pour le transfert d'électrons, tandis que le NADPH a un effet activateur sur l'enzyme.Ces études apportent des éléments importants pour envisager une optimisation ciblée et maîtrisée pour la bioproduction d'H2. / Oxygenic photosynthetic organisms are a matter of great biotechnological interest for the production of dihydrogen using what seem to be infinite resources, water and solar energy. The cyanobacterium Synechocystis sp. PCC 6803 encodes a bidirectional [NiFe] hydrogenase consisting of a pentameric complex (HoxEFUYH) that allows it to carry H2 photoproduction. However, it is a transient process, mainly due to the oxygen sensitivity of hydrogenases, O2 being produced at PSII during photosynthesis. Future exploitation of these organisms in bioprocesses requires a better understanding of the molecular bases of O2 sensitivity of the hydrogenase and of the elements limiting H2 evolution which involves detailed knowledge of the interactions of the enzyme with its physiological partners NAD(P)+/NAD(P)H.Various mutants of the Synechocystis hydrogenase were created by genetic engineering, targeting specific amino acid residues (Ileu64, Leu107, Leu112) in the catalytic subunit HoxH identified as putative critical elements for O2 sensitivity. Results obtained in vitro and in vivo indicate that the substitution I64M slightly improves O2 tolerance and alters gas diffusion kinetics with a bias towards H2 production. Studying the interaction of diaphorase gene-deletion mutants hoxF and hoxE with partners NAD(P) showed that NAD+/NADH are the preferential electron acceptor/donor of the hydrogenase, while NADPH is more efficient for enzyme activation.These studies provide first insights on the determinants of the oxygen sensitivity of the hydrogenase of Synechocystis and its activation, which are critical elements to consider in targeted optimization for bioproduction of H2.

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