Les antibiotiques ont été utilisés pour le traitement des infections bactériennes depuis plus de 70 ans, sauvant des millions de vies. Cependant, leur mauvaise et sur-utilisation ont conduit à l’émergence de la résistance bactérienne. Outre le développement de nouvelles familles d'antibiotiques, la détection rapide et sensible de bactéries est très importante pour le diagnostic médical. Les polymères fluorescents représentent un grand potentiel, car ils sont faciles à fonctionnaliser, synthétiser et greffer. Les films sont plus pratiques, faciles à manipuler et peuvent être réutilisés, ce qui n'est pas le cas des méthodes de détection en solution. L’objectif de ce travail est de développer un film de polymère nanostructuré fluorescent et sensible sur des surfaces de verre pour la détection bactérienne. Sur la base de la méthode de polymérisation radicalaire par transfert de chaîne réversible par addition-fragmentation (RAFT), trois types de polyélectrolytes fluorescents à base de BODIPY (FPC) ont été synthétisés : des chaînes relativement courtes à caractère polyélectrolyte faible (SW FPC), des chaînes courtes à caractère polyélectrolyte fort (SS FPC) et enfin des chaînes longues à caractère polyélectrolyte faible (FPC LW). Les films FPC LbL ont été élaborés sur des lames en verre par interaction électrostatique. Les propriétés photophysiques et de surface des FPC LbL ont été contrôlées en ajustant les conditions de dépôt. Les films FPC LbL à base de BODIPY ont été utilisés comme dispositif de première génération pour la détection de E. coli. Dans l'étape suivante, la sensibilité des films a été augmentée en utilisant le principe de fluorescence exaltée par plasmon (Metal Enhanced Fluorescence MEF). Un film LbL -MEF a été préparé et testé pour la détection de bactéries. Des nanoparticules d'or sphériques (Au NPs) ont été synthétisées et recouvertes de poly(chlorhydrate d'allylamine) (PAH). Le FPC LW a été sélectionné comme couche fluorescente. Différents films contenant des Au NPs et LW FPC- ont été fabriqués. La distance entre les NPs Au et LW FPC- a été ajustée par l'ajout de deux polymères de charge opposée (PC + et PC-). Les deux surfaces de AuNP / 4 couches PC / LWFPC- et Au NPs / 8 couches PC / LWFPC- ont montré que E. coli peut être ciblée par LW FPC-.La sélectivité des films LbL a été ajoutée en introduisant un anticorps comme site de reconnaissance spécifique. Le polyanion et le polycation avec le groupe fonctionnel 4-dibenzocyclooctynol (DIBO) ont été assemblés sur des lames de verre activées. L'anticorps anti-E. coli a ensuite été introduit sur la surface en une seule étape via la réaction de cycloaddition azide-alcyne (SPAAC). Le nombre d'E. coli capturées dépend de la concentration d’anticorps sur la surface. La surface a montré une sélectivité significative pour E. coli, comparée à B. subtilis.La croissance bactérienne peut être détectée sur un film mince LbL en introduisant un fluorophore sensible au pH (fluorescéine). En effet, la croissance des bactéries est souvent associée à une diminution du pH du milieu due à une libération de métabolites acides. Nous avons préparé avec succès différents types de films LbL sensibles au pH. Dans un premier temps, la synthèse de différents polyanions fonctionnalisés (chaîne courte et longue de DIBO-PC et polymère fluorescent rouge) a été achevée. Ensuite, trois types de surfaces sensibles au pH contenant de la fluorescéine (DIBO-SWPC- / fluorescéine, DIBO-LW PC- / fluorescéine et ratiométrique RFPC- / fluorescéine) ont été préparés sur la base d'assemblage LbL et de chimie click. Enfin, trois surfaces sensibles au pH ont été étudiées pour la détection de la croissance des bactéries. Toutes les surfaces étaient biocompatibles, le nombre de E. coli augmentait même après plusieurs heures d'incubation sur chaque surface. La détection par le changement de fluorescence est en cours de développement. / Antibiotics have been used for the treatment of bacterial infections for over 70 years, saving millions of lives. The current antibiotic resistance crisis has been attributed to the overuse and misuse of these medications. Therefore, the prevention of infection transmission by the rapid and sensitive detection of antibiotic resistant strains is needed in managing this crisis. Fluorescent polymers show great potential for bacteria detection, because they are easy to functionalize, reproduce and graft. Compared with the methods used for bacterial detection in liquid, bacterial detection on a film surface is more convenient, easier to handle and is applied in devices that can be easily reused. The goal of my PhD work is to develop fluorescent and sensitive nanostructured polymer films on surfaces for bacterial detection. Three types of BODIPY-based fluorescent polyelectrolytes (FPC) with different features were synthetized based on reversible addition-fragmentation transfer (RAFT) polymerization: relatively Short chains and Weak polyelectrolytes (SW FPC), Short chains and Strong polyelectrolytes (SS FPCs) and Long chains and Weak polyelectrolytes (LW FPCs). FPC LbL films were fabricated on activated glass slides by means of electrostatic attraction. The photophysical and surface properties of FPC LbL fims were easily controlled by adjusting the deposition conditions.The following step aimed at increasing the films’ sensitivity by using the metal-enhanced fluorescence (MEF) principle. A MEF based LbL film was prepared and tested for bacteria detection. Spherical gold nanoparticles (Au NPs) were synthesized and coated with poly(allylamine hydrochloride) (PAH). The LW FPC- was selected as the fluorescent layer. Different films containing Au NPs and LW FPC- were fabricated and the distance between the Au NPs and LW FPC- was adjusted by changing the numbers of layers with two oppositely charged polymers (PC+ and PC-). Both Au NPs/4 layers PCs/LWFPC- and Au NPs/8 layers PCs/LWFPC- surfaces indicated that E. coli can be detected by LW FPC-.The selectivity of LbL films was added by introducing an antibody on the surface of the film to provide specific recognition of a chosen bacterial strain. This LbL surface achieved a rapid, effective and specific detection of E. coli bacteria. The polyanion and polycation with a 4-dibenzocyclooctynol (DIBO) functional group were assembled on the activated glass slides and an anti-E. coli antibody containing an azide group was efficiently introduced on the surface in a single step based on the azide-alkyne cycloadditions (SPAAC) reaction. The number of E. coli captured on the surface was shown to be dependent on the amount of antibody on the surface. The anti-E. coli antibody surface showed significant selectivity for E. coli, compared with B. subtilis. An alternative approach is to detect bacterial growth on thin LbL film by introducing pH sensitive fluorophore (fluorescein). The growth of bacteria is often associated with a decrease in pH of the growth medium due to a release of acidic metabolites. Different types of pH sensitive LbL film were prepared and tested for the detection of bacterial growth. Firstly, the synthesis of different functionalized polyanions (short and long chain of DIBO-PC- and red fluorescent polymer) was carried out. Three types of pH sensitive surfaces containing fluorescein (DIBO-SWPC-/fluorescein, DIBO-LW PC-/fluorescein and ratiometric RFPC-/fluorescein surfaces) were prepared based on the combination of LbL assembly and copper-free click chemistry. Finally, three pH sensitive surfaces were studied for bacteria growth detection. All the surfaces were shown to be biocompatible, the number of E. coli increased after several hours of incubation on each surface, as detected by brightfield microscopy imaging. The application for the fluorophore-dependent detection of bacterial growth remains to be developed.

Les nanostructures périodiques jouent un rôle important dans le domaine des nanotechnologies, en particulier dans le contrôle des photons. Bien qu'il existe de nombreuses techniques d'usage général pour la fabrication et la simulation optique, nous avons développé une technique de fabrication sur mesure et une méthode de simulation optiques pour les structures périodiques pour accélérer le prototypage à l’échelle du laboratoire et la conception optique. Dans la première partie de cette thèse, nous décrivons une technique lithographique nommée « Laser Interference Lithography » (LIL) à faible coût pour la fabrication de nanostructures périodiques. La technique LIL est combinée avec gravure sèche, gravure humide et technique de gravure électrochimique pour réaliser, respectivement, des trous cylindriques, des pyramides inversées et des réseaux taux de pores bi-périodiques à facteur d’aspect élevé sur le substrat à base de silicium. Les modèles unidimensionnels sur des substrats en verre sont également utilisés comme nanofiltres dans la réalisation de la puce de pré-concentration à faible coût. Dans la deuxième partie, nous décrivons d'abord une méthode de calcul électromagnétique rigoureuse Rigorous Coupled-Wave Analysis (RCWA) conçu pour les structures périodiques. Une description détaillée est donnée pour expliquer la méthode numérique. Ensuite, nous combinons la méthode RCWA et une nouvelle approche proposée de la conception des modèles pseudo-désordonnée pour améliorer le piégeage des photons. A titre d'exemple, nous démontrons que, en ajoutant des structures désordonnées à petite échelle sur des arrangements périodiques à grande échelle, la performance quant à l’absorption des couches minces de silicium peut être grandement améliorée. / Periodic nanostructures play an important role in the domain of nanotechnology, especially in photon control. While there exist many general purpose techniques for fabrication and optical simulation, we show tailored fabrication and optical simulation methods for periodic structures to accelerate lab-scale prototyping and optical design. In the first part of this dissertation, we describe a low-cost lithographic technique named Laser Interference Lithography (LIL) for fabricating periodic nanostructures. LIL technique is combined with dry-etching, wet-etching and electrochemical etching technique to realize, respectively, cylindrical holes, inverted pyramids and high aspect ratio pore arrays on silicon based substrate. The one-dimensional patterns on glass substrates are also used as nanofilters in realizing low-cost preconcentration chip. In the second part, we first describe Rigorous Coupled-Wave Analysis (RCWA), a rigorous electromagnetic calculation method designed for periodic structures. A detailed derivation is given to explain the numerical method. Then, we combine the RCWA method and a new proposed pseudo-disordered patterns design approach to investigate photon control. As an example, we demonstrate that by adding ‘appropriate’ engineered fine stripes to each long period the absorption performance of thin silicon slab can be largely enhanced.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Thesis advisor: Dunwei Wang / Photosynthesis converts solar energy and stores it in chemical forms. It is one of the most important processes in nature. Artificial photosynthesis, similar to nature, can provide us reaction products that can potentially be used as fuel. This process promises a solution to challenges caused by the intermitted nature of solar energy. Theoretical studies show that photosynthesis can be efficient and inexpensive. To achieve this goal, we need materials with suitable properties of light absorption charge separation, chemical stability, and compatibility with catalysts. For large-scale purpose, the materials should also be made of earth abundant elements. However, no material has been found to meet all requirements. As a result, existing photosynthesis is either too inefficient or too costly, creating a critical challenge in solar energy research. In this dissertation, we use inorganic semiconductors as model systems to present our strategies to combat this challenge through novel material designs of material morphologies, synthesis and chemical reaction pathways. Guided by an insight that a collection of disired properties may be obtained by combining multiple material components (such as nanostructured semiconductor, effective catalysts, designed chemical reactions) through heterojunctions, we have produced some advanced systems aimed at solving fundamental challenges common in inorganic semiconductors. Most of the results will be presented within this dissertation of highly specific reaction routes for carbon dioxide photofixation as well as solar water splitting. / Thesis (PhD) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis advisor: Zhifeng Ren / Solid state cooling and power generation based on thermoelectric principles are regarded as one of the technologies with the potential of solving the current energy crisis. Thermoelectric devices could be widely used in waste heat recovery, small scale power generation and refrigeration. It has no moving parts and is environmental friendly. The limitation to its application is due to its low efficiency. Most of the current commercialized thermoelectric materials have figure of merit (ZT) around 1. To be comparable with kitchen refrigerator, ZT is required at room temperature. Skutterudites have emerged as member of the novel materials, which potentially have a higher ZT. In the dissertation, my investigation will be focused on the optimization of CoSb₃ &ndash based skutterudites. Starting with Co and Sb elements, CoSb₃ will form through a high energy ball mill. Unfortunately, even after 20 hours, only a small percentage of the powders have transformed in into CoSb₃. Then the powders will be compacted into bulk samples by DC-controlled hot press. CoSb₃ single phase will form after press. Characterization of the structure and thermoelectric properties will be presented with details. The effects of synthesis conditions on thermoelectric properties of skutterudites were studied and discussed. Several possible methods of improving the ZT of N type skutterudites were applied. The highest obtained ZT thus far is about 1.2 from Yb doped CoSb₃. For a group of samples with nominal composition Yb_xCo₄Sb₁₂, the increased Yb concentration in our samples not only enhanced the power factor due to electron doping effect but also decreased the thermal conductivity due to a stronger rattling effect. In addition, the increased grain boundary density per unit volume due to the small grains in our bulk skutterudite materials may have also helped to enhance the phonon scattering and thus to reduce the thermal conductivity. Single and double doping methods with different combinations were also tried. So far, none of them have surpassed ZT of 1.2. Mixing different materials with Yb_0.35Co₄Sb₁₂ so far to increase the phonon scattering was also performed. No dramatic thermal conductivity reduction was observed. Small amounts of Fe/Mn substitution on Co sites will decrease the power factor to undesired degrees. Some results with Nd filled P type sample will be briefly introduced. P type samples are also obtained through substitution on Sb site. Preliminary work on preparing the electrode for CoSb₃ will be presented in the dissertation. CoSi₂ has low resistivity, and a similar coefficient of thermal expansion (CTE) as of doped CoSb₃. It is good electrode candidate. DC controlled hot press is used to make the contact. Thermal stability of the contact was tested. Small cracks will form in the contact area, further improvement is necessary. Finally, my previous work on ZnO nanowire growth is briefly introduced. Large throughput of ZnO nanowire could be obtained with NaCl as the support to promote the conversion of Zn powder to ZnO. / Thesis (PhD) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Designing self-assembling DNA nanostructures often requires the identification of a route for a scaffolding strand of DNA through the target structure. When the target structure is modeled as a graph, these scaffolding routes correspond to Eulerian circuits subject to turning restrictions imposed by physical constraints on the strands of DNA. Existence of such Eulerian circuits is an NP-hard problem, which can be approached by adapting solutions to a version of the Traveling Salesperson Problem. However, the author and collaborators have demonstrated that even Eulerian circuits obeying these turning restrictions are not necessarily feasible as scaffolding routes by giving examples of nontrivially knotted circuits which cannot be traced by the unknotted scaffolding strand. Often, targets of DNA nanostructure self-assembly are modeled as graphs embedded on surfaces in space. In this case, Eulerian circuits obeying the turning restrictions correspond to A-trails, circuits which turn immediately left or right at each vertex. In any graph embedded on the sphere, all A-trails are unknotted regardless of the embedding of the sphere in space. We show that this does not hold in general for graphs on the torus. However, we show this property does hold for checkerboard-colorable graphs on the torus, that is, those graphs whose faces can be properly 2-colored, and provide a partial converse to this result. As a consequence, we characterize (with one exceptional family) regular triangulations of the torus containing unknotted A-trails. By developing a theory of sums of A-trails, we lift constructions from the torus to arbitrary n-tori, and by generalizing our work on A-trails to smooth circuit decompositions, we construct all torus links and certain sums of torus links from circuit decompositions of rectangular torus grids. Graphs embedded on surfaces are equivalent to ribbon graphs, which are particularly well-suited to modeling DNA nanostructures, as their boundary components correspond to strands of DNA and their twisted ribbons correspond to double-helices. Every ribbon graph has a corresponding delta-matroid, a combinatorial object encoding the structure of the ribbon-graph's spanning quasi-trees (substructures having exactly one boundary component). We show that interlacement with respect to quasi-trees can be generalized to delta-matroids, and use the resulting structure on delta-matroids to provide feasible-set expansions for a family of delta-matroid polynomials, both recovering well-known expansions of this type (such as the spanning-tree expansion of the Tutte polynnomial) as well as providing several previously unknown expansions. Among these are expansions for the transition polynomial, a version of which has been used to study DNA nanostructure self-assembly, and the interlace polynomial, which solves a problem in DNA recombination.

Incorporating nanotechnology into polymers has tremendous potential to improve the functionality and performance of polymer materials for use in a wide range of biomedical and industrial applications. This research uses lyotropic liquid crystals (LLCs) to control polymer structure on the nanometer scale in order to improve material properties. The overall goal of this research is to establish fundamental methods of synthesizing polymers with controlled nanostructured architectures in order to understand and utilize useful property relationships that result from the organized polymer morphologies. This work aims to establish a fundamental understanding of the reaction conditions needed to control polymer nanostructure and determine the benefits of organized polymer network structures on mechanical and transport properties. The synthesis of nanostructured polymers for improved material performance has utilized LLCs and photopolymerization kinetics to direct polymer structure. Self-assembled LLC phases provide a useful template that may be used as a photopolymerization platform to control polymer morphology on the nanometer size scale. Photopolymerization kinetics were used as a tool to examine the thermodynamics and phase structure evolution that occurs during the polymerization reaction. Additionally, several methods were developed to control polymer morphology and prevent loss of LLC order that can occur during polymerization. LLCs were also used to generate nanocomposite polymers with two distinct polymer networks to impart improvements in material properties. Other useful property relationships including increases in mechanical integrity, greater diffusive transport, and larger water uptake were established in this research. Finally, the LLC templating process was applied to solve performance problems associated with stimuli-sensitive polymer materials. Dramatic improvements in the response rate, dynamic range, and mechanical properties were achieved using LLCs and photopolymerization to control polymer nanostructure. This work has established fundamental tools that can be used to understand and control the evolution of polymer structure during the polymerization reaction in order to improve polymer properties. Ultimately, the enhanced properties generated by the nanostructured polymer network can be used to improve the functionality of polymers.

Solar hydrogen has the potential to replace fossil fuels with a sustainable energy carrier that can be produced from sunlight and water via &quotewater splitting&quote. This study investigates the use of hematite (Fe&sub2O&sub3) as a photoelectrode for photoelectrochemical water splitting. Fe&sub2O&sub3 has a narrow indirect band-gap, which allows the utilization of a substantial fraction of the solar spectrum. However, the water splitting efficiencies for Fe&sub2O&sub3 are still low due to poor absorption characteristics, and large losses due to recombination in the bulk and at the surface. The thesis investigates the use of nanostructured composite electrodes, where thin films of Fe&sub2O&sub3 are deposited onto a nanostructured metal oxide substrate, in order to overcome some of the factors that limit the water splitting efficiency of Fe&sub2O&sub3. Doped (Si, Ti) and undoped Fe&sub2O&sub3 thin films were prepared using vacuum deposition techniques, and their photoelectrochemical, electrical, optical and structural properties were characterised. The doped Fe&sub2O&sub3 exhibited much higher photoelectrochemical activity than the undoped material, due to an improvement of the surface transfer coefficient and some grain boundary passivation. Schottky barrier modeling of Fe&sub2O&sub3 thin films showed that either the width of the depletion region or the diffusion length is the dominant parameter with a value around 30 nm, and confirmed that the surface charge transfer coefficient is small. An extensive review of the conduction mechanisms of Fe&sub2O&sub3 is presented. ZnO and SnO&sub2 nanostructures were investigated as substrates for the Fe&sub2O&sub3 thin films. Arrays of well-aligned high aspect ratio ZnO nanowires were optimised via the use of nucleation seeds and by restricting the lateral growth of the nanostructures. The geometry of the nanostructured composite electrodes was designed to maximise absorption and charge transfer processes. Composite nanostructured electrodes showed lower quantum efficiencies than equivalent thin films of Fe&sub2O&sub3, though a relative enhancement ofcollection of long wavelength charge carriers was observed, indicating that the nanostructured composite electrode concept is worthy of further investigation. The rate-limiting step for water splitting with Fe&sub2O&sub3 is not yet well understood and further investigations of the surface and bulk charge transfer properties are required in order to design electrodes to overcome specific shortcomings.

Le dopage des nanofils de semiconducteurs est un paramètre essentiel gouvernant leurs propriétés optiques et de transport. Alors que dans les nanofils d'une centaine de nanomètres de diamètre les impuretés servant au dopage se comportent certainement comme dans le matériau massif, les confinements quantique et diélectrique influent fortement sur leur structure électronique pour des dimensions de l'ordre de la dizaine de nanomètres ou en dessous. Les récentes techniques de croissance des nanofils semiconducteurs ouvrent de grandes opportunités pour des applications à l'échelle nanométrique. Ils restent semiconducteurs indépendamment de leur diamètre et de leur orientation, donnant la possibilité de contrôler leurs propriétés par dopage. Alors qu'il n'y a pas de doute que des nanofils de type p et n peuvent être produits, la question sur « comment leur conductivité électrique dépend du dopage ? » reste largement ouverte. En fait, la plupart des travaux montrant de bonnes propriétés de transport concernent des nanofils dopés avec une forte concentration de dopants (près de la densité de Mott ou au dessus). Dans ce cadre, notre travail présentera les résultats de calculs de structure électronique d'impuretés hydrogénoïdes dans des nanofils de silicium. L'évolution de l'énergie de liaison des donneurs et accepteurs sera présentée en fonction de la taille des nanofils. Des simulations de l'efficacité de dopage à température ambiante permettront de prédire des caractéristiques essentielles du transport électronique dans les nanofils. Nous montrons que l'énergie de liaison croit, dû aux confinements. Le confinement quantique pour les petites tailles de nanofils (diamètre < 5 nm) et le confinement dit « diélectrique » qui se produit quand il y a une importante discontinuité entre la constante diélectrique dans le nanofil et celle de son environnement. Pour les nanofils dans un environnement avec une faible constante diélectrique, nous montrons que les impuretés ne peuvent être ionisées à température ambiante même pour des diamètres jusqu'à quelques dizaines de nanomètres. Nous expliquons l'origine de ce comportement en considérant l'effet du potentiel de l'impureté et de la self-énergie des porteurs, nous donnons l'énergie d'ionisation dans différentes configurations. Ces résultats nous permettent de conclure qu'un fort dopage est nécessaire pour obtenir de bonnes propriétés électriques dans le nanofil.

Ce travail de thèse porte sur les liens entre les conditions opératoires du procédé de mise en œuvre par mélange à l'état fondu et la structure de nanocomposites polypropylène/argile, ainsi que sur l'influence de l'état de dispersion de l'argile sur les propriétés mécaniques des matériaux obtenus. L'étude est basée sur des essais expérimentaux. Les analyses structurales sont réalisées en s'appuyant sur la rhéologie, la diffraction de rayons X ainsi que sur des observations en microscopie électronique.Les études en mélangeur interne ont montré, d'une part, que l'augmentation de la concentration en agent compatibilisant (PP-g-MA) favorise la dispersion de l'argile à l'échelle manométrique tout en augmentant la fragilité des nanocomposites, et d'autre part, que le mélange par voie mélange maître permet d'améliorer considérablement l'état de dispersion comparativement à la voie directe. Les essais réalisés en extrusion bivis corotative ont permis de mettre en évidence l'impact de la vitesse de rotation des vis (N), du débit d'alimentation (Q) et de la température de régulation (Trég) sur l'état de dispersion. L'influence de ces trois variables peut être décrite à l'aide d'un paramètre unique : l'énergie mécanique spécifique (EMS). L'accroissement de l'EMS entraîne une augmentation du niveau d'exfoliation jusqu'à une valeur critique au-delà de laquelle les conditions opératoires ne semblent plus influencer l'état de dispersion. Une relation entre le module de Young des nanocomposites et le niveau d'exfoliation a été établie. Le logiciel LUDOVIC© nous a permis de montrer que l'EMS permet également une bonne description de la progression de l'état de dispersion le long du profil d'extrusion. Enfin, l'étude du comportement thixotrope des nanocomposites à l'état fondu a notamment permis de comprendre que le principe de superposition temps-température ne s'applique pas systématiquement aux nanocomposites étant donné leur caractère évolutif.