A DNA molecule passing through a nanopore in a liner and sequential fashion allows for unprecedented interrogation of the polymer. Adding transverse electrodes that are comparable in size and sensitive to the DNA molecule, can further the attempts to rapidly sequence DNA. Carbon nanotubes are comparable in size and interact strongly with the DNA molecule. This makes them an excellent choice for integration with nanopores. Only the section of the carbon nanotube in immediate proximity to the nanopore should be sensitive to the DNA molecules. Atomic layer deposition of metal-oxides passivates the sections of the carbon nanotube that are not to interact with the DNA molecule. The coating also protects the thin film interconnects leading to the carbon nanotube. Hafnium oxide is superior to aluminum oxide in chemical resistance and electrical insulation but leads to a high failure rate of the carbon nanotube across nanopore devices. Aluminum oxide, combined with gold thin film interconnects to the carbon nanotube, produced the first functioning devices in electrolyte. These devices had concurrently functioning ionic (current across the nanopore) and transverse (current through the carbon nanotube) channels. No concurrent DNA translocation signal was recorded on the ionic and nanotube current traces. Analyzing the translocation events recorded on the ionic channel indicated that double-stranded DNA (dsDNA) passed through the carbon nanotube articulated nanopore an order of magnitude slower than it would have through a comparable unarticulated nanopore. The slower translocation observed is a necessary condition for sequencing. Investigating dsDNA translocation under various experimental conditions led to the discovery of a new interaction between the molecule and small nanopores. A dsDNA molecule is trapped when the electric field near the nanopore attracts and immobilizes a non-end segment of the molecule at the nanopore orifice without inducing folded translocation. In this work, the expression “trapped dsDNA” will exclusively refer to the immobilization of a dsDNA molecule at the orifice of the nanopore. The ionic current through the nanopore decreases when the dsDNA molecule is trapped by the nanopore. By contrast, a translocating dsDNA molecule under the same conditions causes an ionic current increase. Finite element modeling results predict this behavior for the conditions of the experiment. / Physics

La unión de las propiedades de los CNT con los principios de reconocimiento molecular se presenta como una base adecuada para el desarrollo de sensores altamente específicos. El objetivo de la presente tesis ha sido desarrollar sensores químicos, del tipo transistores de efecto campo (CNTFET), basados en interacciones receptor-analito, mediante el empleo de los nanotubos de pared sencilla (SWCNT), que actúan como transductores de la señal analítica.Las principales etapas de la parte experimental han sido: Crecimiento de SWCNT con la técnica de deposición química en fase vapor. Integración de los SWCNTs en sistemas CNTFET. Empleo del CNTFET como base del sensor en distintos campos utilizando modelos de reconocimiento molecular. Dependiendo del tipo de funcionalización de los SWCNTs se pueden obtener sensores para proteínas, iones, etc. Como resultado, se han desarrollado y estudiado sensores basados en CNTFETs para la detección distintos analitos de interés, como son la Inmunoglobulina G Humana, los iones potasio y el dióxido de azufre. / The general objective of this thesis is to develop chemical sensors whose sensing capacities are based on the principle of molecular recognition and where the transduction is carried out by single-walled carbon nanotubes (SWCNT).The sensing device used is the carbon nanotube field-effect transistor (CNTFET). The new structure of the CNTFET allows nanotubes to be integrated at the surface of the devices, thus exploiting SWCNTs' sensitivity to changes in their environment. The functionalization of SWCNTs with several types of molecular receptors such as antibodies, ion selective membranes, and synthetic receptors, achieve a high selectivity towards the analyte of interest. This thesis shows that CNTFETs can be used for the successful selective detection of different types of target analytes. These can be biomolecules such as antigens, small compounds such as cations or gas-phase compounds such as SO2.

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No description available.

Field emission cathodes have proven themselves to be excellent candidates for some special medical X-ray applications. Spindt cathode and CNT (carbon nanotube) based field emission cathode have been widely studied for many years. Spindt cathode has the near perfect structure, but the material property limits its applications. On the other hand, low density vertically aligned CNT array has been proved the best candidate of field emission material. Several attempts have been made to combine the advantages of the Spindt cathode and CNT array, but some most important advantages of Spindt cathode have not been successfully utilized in CNT emitter design, for example: ballast resistor, self-aligned fabrication process, sub-micron scale gate electrode, and low control voltage. In this thesis, the design, fabrication and test of CNT based field emission cathode with a novel ballast resistor and coaxial cylinder shape gate electrode is reported. A connection pad has been reported for the first time. This structure makes the ballast resistor can be utilized in a CNT field emitter array. Therefore, the uniformity and stability of field emission current is improved significantly. In addition, the stabilized emission current heated up the sample to a high temperature and changes the emission from field emission to Schottky emission regime. This is the first report of the self-heating Schottky emission from a CNT emitter array. Coaxial cylinder shape gate electrode is another important improvement in the CNT emitter design. The gate electrode adopts the self-alignment property of the Spindt cathode, and adjusted to fit the structure and synthesis process of CNT array. This new design and fabrication process has all the advantages of both the Spindt cathode and CNT emitter. In addition to the field emission cathode design, a novel PMMA (poly methyl methacrylate) based FEM (field emission microscope) is designed to evaluate the emission uniformity and capture high resolution images of the distribution of field emitted electrons. Compare to the conventional phosphor screen based FEM, the PMMA based FEM has a much higher resolution and sensitivity. Images of this new FEM have a resolution of as high as 0.34 nm and clearly show the boundary of crystal facets.

Three dimensional (3D) hybrid architectures are new types of materials that have a number of technological applications. However, the synthesis of such materials has been problematic to date. The objective of this study is to fabricate 3D hybrid architectures composed of sp2-carbon nanomaterials and inorganic nanostructures using a convenient microwave assisted technique. Sp2-Carbon nanomaterials such as carbon nanotubes (CNTs), graphene and its derivative graphene oxide (GO), have been explored by researchers as major components of hybrid materials due to their exceptional electrical, thermal, mechanical and biological properties. However, most of the research has been devoted to the hybrids with randomly dispersed phases. The present study explores the feasibility of using aligned 3D sp2-carbon structures in a bottom-up microwave-assisted chemical synthesis approach to fabricate various 3D sp2-carbon/inorganic hybrid architectures. The carbon nanostructures, either tubular or planar, not only contribute to the functionalities of the hybrids, but also template the ordered assembly of phases on nanometer scale. Mimicking nature is a key to develop novel types of materials with enhanced physical and mechanical properties suitable for advanced applications (e.g. lightweight and yet tough materials that are extensively needed in automotive and aerospace industries). One approach to obtain such materials or devices is to mimic nature processes and synthesize hybrid materials with ordered structures on the nanometer scale. Those functional structures are fabricated in this thesis through an in-situ microwave synthesis of inorganic materials on 3D sp2-carbon architectures. Generally, in chapter 1, it was shown and discussed the procedures to fabricate 3D architectures of carbon nanotubes and graphene oxide as basic components for template synthesis of the hybrids. Then in chapter 2 the microwave chemical synthesis approach was introduced as a convenient route for fabricating inorganic materials such as zinc oxide (ZnO) which was shown to be used as UV sensors. Through photolithography patterning of the iron catalyst thin films on Si/SiO2 substrates, 3D aligned CNT structures were fabricated and were coated in-situ with inorganic materials such as cobalt oxide, zinc oxide and manganese oxide using a microwave synthesis approach (chapter 3). The obtained aligned strips of CNT/Co3O4 were chosen as an example to illustrate the application of such 3D hybrids in energy storage applications. The capacitance of the aligned CNT/Co3O4 strips was measured to be 123.94 F/g. Using graphene oxide as template for manufacturing the 3D sp2-carbon/inorganic hybrid structures, interesting novel layered configurations are obtained that are similar to the layered structures of exoskeleton of the mollusks nacre. The layered hybrid structure shown to be mechanically improved compared to its constituents (chapter 4). Finally in chapter 5, some of the future routes have been proposed for further research on this novel field of 3D hybrid materials composed of sp2-carbons and inorganic nanomaterials.

Carbon nanotubes (CNT) and graphene have been one of the noticeable research areas in science and technology. In recent years, the assembly of these carbon nanostructures is one of the most interesting topic to the scientific world due to its variety of applications from nano to macroscale. These bulk nanostructures to be applicable in shock absorbers, batteries, sensors, photodetectors, actuators, solar cells, fuel cells etc. The present work is motivated to study the detailed compressive behavior of three dimensional cellular assemblies of CNT and graphene. The CNT foams are synthesized by chemical vapor deposition method. It is interesting to study the compressive behavior of CNT foam in the presence external magnetic field applied perpendicular to CNT axis. The peak stress and energy absorption capability of CNT foam enhances by four and nearly two times in the presence of magnetic field as compared to the absence of the magnetic field. In the absence of magnetic field the deformation of CNT foam is obtained elastic, plateau and densification regions. Further CNT foam is loaded with iron oxide nanoparticles of diameter is ~ 40nm on the surface and detailed study of the compressive behavior of the foam by varying iron nanoparticles concentration. The peak stress and energy absorption capability of CNT foam initially decreases with increasing the intensity of the magnetic field, further increases the intensity of the magnetic field the maximum stress and energy absorption capability increases which is due to magnetic CNT and particles align in the direction of the magnetic field. CNT surfaces were further modified by fluid of different viscosities. The mechanical behavior of CNT foam filled with fluids of varying viscosities like 100%, 95% and 90% glycerol and silicone oil are 612, 237, 109 and 279 mPa-s respectively. The mechanical behavior of CNT foam depends on both the intensity of magnetic field and fluid viscosity. The non linear relation between peak stress of CNT and magnetic field intensity is σp(B, η) = σ0 ± α(B-B0) where σ0 is the peak stress at B = B0 , η is the fluid viscosity, parameter α depends on properties of the MR fluid and B0 is an optimum magnetic field for which peak stress is maximum or minimum depending on the fluid viscosity. Graphene is assembled into a three dimensional structure called graphene foam. The graphene foam is infiltrated with polymer and study the detailed compressive behavior of graphene foam and graphene foam/PDMS at different strains of 20, 40, 60 and 70%. The maximum stress and energy absorption capability of graphene foam/PDMS is six times higher than the graphene foam. Also the graphene foam/PDMS is highly stable and reversible for 100 cycles at strains of 30 and 50%. The mechanical behavior of CNT, graphene foam, CNT/PDMS and graphene foam/PDMS is compared. Among all the foams, graphene foam/PDMS has shown the highest elastic modulus as compared to other foams. This behavior can be attributed to the wrinkles formation during the growth of graphene and a coupling between PDMS and interfacial interactions of graphene foam. Therefore it suggests potential applications for dampers, cushions and electronic packaging. Furthermore, the interaction between nanoparticles and polymer in a novel architecture composed of PDMS and iron oxide nanoparticles is studied. The load bearing capacity of uniform composites enhanced by addition of nanoparticles, reaching to a maximum to 1.5 times of the PDMS upon addition of 5wt.% of nanoparticles, and then gradually decreased to 1/6th of PDMS upon addition of 20wt.% of nanoparticles. On the other hand, the load bearing capacity of architectured composites at high strains (≥40%) monotonically increased with addition of nanoparticles in the pillars.

Les macrophages sont une cible cellulaire du VIH-1, et jouent un rôle important dans la pathogenèse virale. Au cours de ma thèse, je me suis intéressée au rôle des macrophages dans la pathogenèse du VIH-1, mais aussi au cours de la co-infection avec Mycobacterium tuberculosis (Mtb), l'agent étiologique de la tuberculose. J'ai tout d'abord participé à une étude mettant en évidence que l'infection par le VIH-1 reprogramme la migration des macrophages, favorisant notamment le mode migratoire protéolytique. Cet effet est médié par l'interaction de la protéine virale Nef avec les protéines de l'hôte Hck et WASP, ce qui conduit à une modification de l'organisation et de la fonction des podosomes, structures impliquées dans la dégradation de la matrice extracellulaire et la migration dépendante des protéases. La meilleure capacité à migrer des macrophages infectés par le VIH-1 in vitro se traduit in vivo par une augmentation du recrutement des macrophages dans différents tissus de souris transgéniques qui expriment la protéine Nef. Ces travaux ont ainsi révélé un nouveau mécanisme par lequel le VIH-1 dissémine dans les tissus, via l'action de Nef dans les macrophages. L'association fréquente du VIH-1 avec Mtb complique le problème de santé publique posé par l'infection virale. En effet, Mtb aggrave la pathogenèse du VIH-1 chez les patients co-infectés. L'étude des mécanismes impliqués et le rôle des macrophages dans ce phénomène constituent les objectifs principaux de ma thèse. J'ai révélé que les macrophages infectés par Mtb génèrent un microenvironnement qui active les macrophages voisins vers un programme de polarisation anti-inflammatoire dit M(IL-10). J'ai mis en évidence que ces macrophages M(IL-10) sont particulièrement efficaces pour la production de VIH-1. J'ai démontré que le microenvironnement associé à la tuberculose entraîne la formation de nanotubes entre les macrophages, grâce à l'activation de la signalisation cellulaire médiée par l'axe IL-10/STAT3. Ces nanotubes, qui favorisent le transfert du virus d'un macrophage à un autre, sont à l'origine de la spectaculaire production de VIH-1 par les macrophages. Nous avons également constaté que ces cellules M(IL-10) s'accumulent dans la circulation sanguine des patients co-infectés ainsi que dans les poumons de primates non-humains co-infectés. Dans l'ensemble, mes travaux identifient les nanotubes comme des acteurs clés dans l'aggravation de la pathogenèse du VIH-1 lors de la co-infection avec Mtb. Ainsi, les nanotubes et la voie de signalisation IL-10/STAT3 pourraient représenter des cibles pour développer de nouvelles thérapies de lutte contre la comorbidité VIH/Mtb. Les résultats obtenus lors de ma thèse contribuent à une meilleure compréhension du rôle des macrophages dans la pathogenèse et la dissémination du VIH-1 dans un contexte de mono-infection, ou lors d'une co-infection avec Mtb. / Macrophages are both crucial host effector cells for HIV-1 and important leukocytes involved in viral pathogenesis. For my doctoral thesis, I was interested in further characterizing the role of macrophages in HIV-1 pathogenesis, and during co-infection with Mycobacterium tuberculosis (Mtb), the etiological agent for tuberculosis (TB). I first participated in a study that provided evidence that HIV-1 infection reprograms the migration of macrophages, particularly by triggering the protease-dependent migration mode. This effect was mediated by the interaction of the viral protein Nef with the host proteins Hck and WASP, which leads to modification in the organization and proteolytic activity of podosomes, important structures for protease-dependent migration. The higher migration capacity of HIV-1-infected macrophages translated in vivo by an increase in the recruitment of macrophages in several tissues of Nef-transgenic mice. This work revealed a novel mechanistic understanding of how HIV-1 infection drives macrophages into tissues, contributing to viral dissemination and possibly creating a hidden cellular reservoir of virus. Worsening this public health issue posed by the HIV-1 epidemic is the frequent association of the virus with Mtb. Indeed, Mtb aggravates HIV-1 pathogenesis in co-infected individuals. Yet, the mechanisms involved in this process are still poorly understood, including the contribution of macrophages. To investigate how Mtb exacerbates the HIV-1 infection in human macrophages was the main focus of my thesis. First, I revealed that Mtb-infected macrophages generate a microenvironment that drives bystander macrophages towards phenotypic and functional features of the so-called M(IL-10) anti-inflammatory program. I found that these M(IL-10) macrophages are highly efficient for HIV-1 production. I demonstrated that the TB-associated microenvironment induces the formation of macrophage-to-macrophage connecting tunneling nanotubes (TNTs) through the IL- 10/STAT3 axis, a phenomenon that is responsible for the dramatic increase of HIV-1 production in M(IL-10) macrophages. Moreover, I provided evidence that M(IL-10) cells are expanded in the peripheral blood of co-infected patients and accumulate in the lungs of co-infected non-human primates. Altogether, this central part of my PhD thesis sheds light to TNTs as key players in the aggravation of HIV-1 pathogenesis in human macrophages during co-infection with Mtb. Thus, this cellular mechanism (together with the IL- 10/STAT3 axis) could represent an unexpected target to develop novel therapeutics against AIDS/TB co-morbidity. Collectively, the results obtained during my thesis contribute to a better understanding of the role of macrophages during HIV-1 pathogenesis and their ability to disseminate the virus in a mono-infection context, or during co-infection with Mtb.

VERÇOSA, Daniel Gomes. Torção natural em nanotubos de carbono de parede simples. 2012. 80 f. Dissertação (Mestrado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2012. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-10-16T21:41:19Z No. of bitstreams: 1 2012_dis_dgvercosa.pdf: 3436247 bytes, checksum: 0a1188195cc191e1fbc8767d711104c7 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-10-21T20:37:48Z (GMT) No. of bitstreams: 1 2012_dis_dgvercosa.pdf: 3436247 bytes, checksum: 0a1188195cc191e1fbc8767d711104c7 (MD5) / Made available in DSpace on 2015-10-21T20:37:48Z (GMT). No. of bitstreams: 1 2012_dis_dgvercosa.pdf: 3436247 bytes, checksum: 0a1188195cc191e1fbc8767d711104c7 (MD5) Previous issue date: 2012 / A mais recente revolução tecnológica vem surgindo através de avanços na área da nanotecnologia, onde se destacam materiais nanométricos como os nanotubos de carbono de parede simples (SWNTs). Esse novo material, descoberto em 1993, têm gerado grande interesse acadêmico e industrial devido às suas propriedades físicas únicas. Trabalhos recentes indicam que essas propriedades são extremamente sensíveis a diversos tipos de deformação estruturais, como aquelas de natureza axial, radial e torcional. Neste trabalho estudamos teoricamente como a estrutura eletrônica dos SWNTs, e consequentemente suas propriedades, reagem à presença de torção. Utilizamos o modelo Tight-Biding estendido (ETB) para calcular a estrutura de bandas dos tubos. A simulação de torção é feita a partir de vínculos específicos que altera a componente angular dos vetores primitivos da rede do grafeno. Para obtermos a configuração mais estável dos SWNTs, utilizamos um método denominado gradiente simples modificado de modo a minimizarmos sua energia total. Foi observado que nanotubos quirais apresentam um valor de torção diferente de zero, denominada torção natural, no seu estado fundamental. Essa torção decresce, de forma universal, com o inverso do cubo do diâmetro. Por sua vez, a dependência da torção natural com o ângulo quiral varia de acordo com a metalicidade do SWNT. As energias de transição ótica para o tubo naturalmente torcionado e não torcionado são comparadas, sendo observado variações de até 50% no minigap de tubos metálicos. Por fim, discutimos quais as possíveis implicações da presença da torção natural na ciência por trás dessa nanoestrutura de carbono.

Made available in DSpace on 2015-05-14T12:14:13Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 10643873 bytes, checksum: 81e90e644eae7a4b72cfe4d225c4e791 (MD5) Previous issue date: 2013-09-20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this work, we have performed first-principles calculations studie the energetic and stability and electronic structure of BxCyNz nanotubes and nanoribbons through the use of calculations based on Density Functional Theory implemented in the SIESTA code. Firstly we have considered zigzag and armchair carbon nanotubes. Then, we have substituted carbon atoms by boron and nitrogen atoms; therefore it is generated island of BN in carbon nanotube. It is found that BN island induces modifications on the electronic structure of such nanotubes, which can induced an opening or closing in the energy gap, depending on chirality, number of rings and diameter of these nanotubes. In addition, it is shown that the spin polarization of BC2N nanoribbons depends on both widths and configurations of such nanostructures. It is also seen that zigzag and armchair BC2N nanoribbons present a gap energy that strongly depends on width of nanoribbons. In addition, a magnetic behavior is observed for the zigzag structures for all widths considered as the armchair show no magnetization. / Neste trabalho realizamos um estudo ab-initio da estabilidade energética e da estrutura eletrônica de nanotubos e nanofitas BxCyNz através do uso de cálculos baseados na Teoria do Funcional da Densidade implementado no código SIESTA. Primeiramente consideramos o nanotubo de carbono zigzag e armchair puro, e fomos adicionando um anel de BN até a quantidade de dez anéis. Em seguida, partimos do nanotubo de carbono com um anel de BN, e fizemos um estudo em função do diâmetro. Encontramos que a presença do anel de BN pode interferir nas propriedades eletrônicas dos nanotubos, podendo provocar abertura ou o fechamento do gap, de acordo com a quiralidade, o número de anéis e o diâmetro do nanotubo. Além da estabilidade e da estrutura eletrônica, também estudamos as propriedades magnéticas de fitas BC2N saturadas com hidrogênio, com diferentes larguras e configurações. Em particular, para BC2N compostas por ilhas de nitreto de boro rodeadas por átomos de carbono com bordas zigzag e armchair. Foi visto que fitas BC2N zigzag e armchair podem ter um pequeno gap semicondutor ou ser metálica dependendo da largura da fita. Além disso, um comportamento magnético é observado para as estruturas zigzag, para todas as larguras consideradas, enquanto as armchair não mostram qualquer magnetização.