Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-03-28T13:13:15Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Cabral Filho, PE Tese - PPGCB.pdf: 40667296 bytes, checksum: 0fe805957d5ab95d53bed853da61deb5 (MD5) / Made available in DSpace on 2017-03-28T13:13:15Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Cabral Filho, PE Tese - PPGCB.pdf: 40667296 bytes, checksum: 0fe805957d5ab95d53bed853da61deb5 (MD5) Previous issue date: 2016-07-15 / CAPES / Os pontos quânticos ou quantum dots (QDs) são nanocristais fluorescentes de semicondutores com propriedades ópticas únicas, tendo como principais vantagens: (1) alta resistência à fotodegradação, possibilitando o acompanhamento de eventos biológicos em tempo real e, (2) superfície ativa, permitindo a conjugação a biomoléculas que vão propiciar especificidade às marcações, além de possibilitar também sua ligação a outras nanopartículas. Com isso, é possível quantificar uma variedade de biomoléculas em células e tecidos e desenvolver nanossondas bimodais (magnético-fluorescentes) baseadas em QDs. O desenvolvimento de nanopartículas bimodais pode aliar as vantagens das técnicas baseadas em fluorescência com as de imagem por ressonância magnética (IRM). Entretanto, a obtenção de sondas bimodais é ainda um desafio, pois durante a conjugação devem ser mantidas as propriedades fluorescentes e magnéticas das nanopartículas, e com isso ainda há poucos trabalhos que façam aplicações em sistemas biológicos. O objetivo desta tese se caracteriza pelo desenvolvimento de sondas com propriedades multimodais baseadas em QDs de Telureto de Cádmio (CdTe) associadas a nanopartículas magnéticas de óxido de ferro como marcadores sítio-específicos em células cancerígenas. Inicialmente os QDs foram conjugados covalentemente à transferrina (Tf) [QDs-Tf] para a quantificação específica de seus receptores (TfRs) em células HeLa e em duas linhagens de glioblastoma (U87 e DBTRG). Através de ensaios de saturação do TfR, foi possível inferir sobre a taxa de renovação deste receptor nessas células. Os resultados mostraram que as células HeLa e as DBTRG possuem uma maior quantidade do TfR quando comparadas às U87. As DBTRG apresentaram maior taxa de renovação do TfR, quando comparadas aos outros dois tipos, demonstrando que os conjugados QDs-Tf são potenciais ferramentas para o estudo da biologia celular do câncer. Posteriormente, nanossondas bimodais (QDsMNPs), baseadas em QDs associados a nanopartículas magnéticas de óxido de ferro, foram obtidas por conjugação covalente. De acordo com as caracterizações, QDs-MNPs mantiveram suas propriedades ópticas e magnéticas e apresentaram-se como potenciais sondas inespecíficas para fluorescência e para aquisição de imagens por RM ponderadas em T2 (tempo de relaxação nuclear transversal). A conjugação prévia dos QDs a Tf, além de fornecer informações sobre a biologia do câncer, auxiliou também na padronização da marcação específica do TfR em células cancerígenas e no estabelecimento de protocolos de conjugação das sondas bimodais a Tf. Por fim, as QDs-MNPs foram conjugadas covalentemente a Tf e essa nova sonda multimodal [(QDs-MNPs)-Tf] reconheceu especificamente os TfR em células HeLa. As caracterizações indicaram que o sistema multimodal não apresentou alteração significativa nas propriedades ópticas e exibiu uma maior relaxividade transversal (r2), se mostrando igualmente potencial sonda para análise por fluorescência e IRM ponderada em T2. Neste trabalho foram obtidas nanossondas promissoras para serem aplicadas na compreensão da biologia celular do câncer, além de auxiliar em métodos diagnósticos e terapêuticos para essa doença. / Quantum dots (QDs) are fluorescent semiconductor nanocrystals with unique optical properties, which have as major advantages: (1) the high resistance to photobleaching, making possible to monitor biological events in real-time and, (2) active surface, allowing the conjugation not only with biomolecules for specific labeling, but also to other nanoparticles. Thus, it would be possible to quantify a variety of biomolecules in cells and tissues, as well as to develop bimodal nanoprobes (fluorescent-magnetic) [BNPs] based on QDs. The development of BNPs can help to combine the advantages of the fluorescence with the resonance magnetic imaging techniques. However, the preparation of bimodal probes can still be considered a challenge, since the fluorescent and magnetic nanoparticles’ properties need to be preserved after conjugation. Therefore, there are still few works applying BNPs in biological studies. The aim of this thesis was to develop nanoprobes, with multimodal properties, based on cadmium telluride (CdTe) QDs conjugated with iron oxide magnetic nanoparticles (MNPs), for site-specific labeling in cancer cells. For this, initially, QDs were covalently coupling to transferrin (Tf) [QDs-Tf] and used to quantify the transferrin receptor (TfRs) in HeLa cells as well as in two glioblastoma lines (U87 and DBTRG). Furthermore, by a TfR saturation assay, it was possible to study the recycling rate of this receptor in cells studied. The results showed that HeLa and DBTRG cells present a higher amount of TfRs when compared to U87. DBTGR showed a higher TfR recycling rate, when compared to the other two lineages, demonstrating that QDs-Tf conjugates are potential tools to study the cancer cell biology. BNPs, based on the conjugation of QDs with MNPs (QDs-MNPs), were obtained by covalent coupling. According to characterizations, the BNPs remained with their optical and magnetic properties preserved and showed to be potential unspecific probes for fluorescence analysis and for T2-weighted magnetic resonance imaging (MRI) acquisition. The conjugation of QDs to Tf, performed previously, was a valuable step not only to provide us information about the biology of cancer cells, but also for the standardization of TfR specific labeling and the establishment of protocol to conjugate the BNPs with Tf. Therefore, QDs-MNPs were also covalently coupling to Tf and this new multimodal nanotool [(QDs-MNPs)Tf] was also able to recognize specifically TfRs in HeLa cells. The multimodal nanosystems presented their fluorescent properties practically unchanged and also exhibited a higher transversal relaxivity (r2), when compared to bare BNPs, showing likewise potential to be used for fluorescence and T2-weighted MRI analyses. In this work, it was developed promising nanoprobes, able to be applied for the cancer cell biology comprehension, and with potential for helping in the improvement of diagnostic and therapeutic methods for this disease.

Les propriétés des quantum dots (QDs) en font des sondes adaptées à la reconnaissance moléculaire. Leur pic d’émission en fluorescence est très étroit et ajustable, tandis que la section efficace de leur spectre d’absorption est très large. En outre, ils sont très brillants et résistent mieux au photoblanchiment que les colorants organiques conventionnels.Notre objectif a été de concevoir un nouveau type de sondes fluorescentes pour une détection rapide à l’échelle de la molécule unique. L’utilisation d’agrégats contenant plusieurs milliers de QDs, plutôt que celle de QDs individuels, permet d’accroître le signal de fluorescence et de simplifier les modalités de détection. La morphologie et la chimie de surface des premiers agrégats préparés n’ont pas pu être contrôlées en les recouvrant avec des molécules de surfactants courts ou une couche de polymère en solution aqueuse. La stratégie centrale de ce manuscrit a permis d’assembler les QDs en nanobilles (NBs) monodisperses de quelques centaines de nanomètres de diamètre, encapsulées dans une couche de silice Stöber. Leur stabilité colloïdale et leur photostabilité ont ainsi été conservées. Un nouveau type d’hybride polymère-silane a été greffé sur la silice. Il présente des chaînes zwittérioniques, garantissant la solubilité en milieu aqueux et une adsorption non spécifique minimale, ainsi que des fonctions réactives pour la bioconjugaison. La réactivité de NBs fonctionnalisées par de la streptavidine avec des billes commerciales biotinylées a été démontrée. Nos résultats préliminaires ont également montré que les NBs peuvent être intégrées dans un dispositif microfluidique pour être comptées individuellement. / Using nanotechnology for molecular diagnostics holds many advantages e.g. an improvement in the simplicity and the sensitivity of analysis. Semi-conductor nanocrystals or quantum dots (QDs) demonstrate several unique properties that make them suitable probes for biomolecular recognition. These QDs present narrow size-tunable emission spectra and a broad excitation spectrum; in addition, they offer higher photostability and brightness than conventional organic dyes. Our aim was to design a new diagnostic probe based on fluorescent nanobeads containing QDs, envi-sioned as a tool for fast and single-molecule detection. An even brighter fluorescence and easily detectable analytical signals could indeed be achieved by aggregating several thousand of QDs together, as compared to single QDs. Coating QD clusters with small surfactants or a polymer layer didn’t provide morphological control or a suitable surface chemistry for bioconjugation. The strategy that we developed consists in self-assembling QDs into monodisperse nanobeads of a few hundreds of nanometers in diameter, on top of which a silica shell was grown by a Stöber-inspired process. This allowed us to protect their colloidal and photo-stability. A new type of multidentate polymer-silane hybrid was subsequently grafted onto the silica shell, presenting a zwitterionic chain for water solubility and antifouling, as well as reactive functions for conjugation with biomolecules. We succeeded in reacting streptavidin-conjugated nanobeads with commercial biotinylated beads. Preliminary results have also shown that we can integrate the nanobeads into a microfluidic system for an efficient single-particle counting.

Les nitrures d’éléments III sont des matériaux clés du fait de leurs excellentes propriétésoptoélectroniques. Ces semi-conducteurs possèdent trois polymorphes de structure et desbandes interdites allant de l’ultraviolet (GaN, AlN) à l’infrarouge (InN).Dans un premier temps, ces travaux se concentrent sur l’élaboration en continu denitrure de gallium (GaN) à partir d’un précurseur unique : le tris(diméthylamido) gallaneemployé dans un solvant anhydre (nitrurant ou non-nitrurant) en conditions supercritiquesdans un réacteur microfluidique. Les particules obtenues présentent des tailles nanométriques(~3 nm) et une structure cristalline complexe. Des luminescences intenses dans l’UV, décaléesvers de plus hautes énergies comparées aux matériaux massifs sont mesurées pour cesmatériaux, en accord avec des phénomènes de confinement quantique. L’absence d’émissiondans le visible permet de démontrer la quasi-absence de défauts dans les nitrures élaborés.Dans un second temps, l’étude porte ensuite sur la préparation de la solution solide InxGa1-xN(0 ≤ x ≤ 1). L’approche choisie est différente : la mise en contact d’une source d’azote et d’unesource métallique est ici privilégiée. Le travail de chimie exploratoire effectué sur les différentstypes de précurseurs envisagés met en avant l’intérêt des cupferronates combinés avec leHMDS pour l’élaboration de nanoparticules d’(InGa)N. Un mélange intime et une répartitionhomogène des deux atomes métalliques sont démontrés pour toutes les compositions et sontconfirmés par l’étude des propriétés optiques. Un décalage de l’énergie maximale d’émissionavec l’augmentation du taux d’indium (jusqu’à 40 %) en adéquation avec les valeurs attenduesest mesuré, permettant d’enregistrer des signaux de l’UV jusqu’au rouge. / LII-nitrides are key materials thanks to their excellent optoelectronic properties. Thesesemiconductors have three structural polymorphs and a wide range of bandgaps can beaccessed varying the composition from ultraviolet (GaN, AlN) to infrared (InN).First, this study focuses on the synthesis of gallium nitride from a single source precursor– the tris(dimethylamido) gallane – employed in an anhydrous solvent in supercriticalconditions in a microfluidic reactor. The as-prepared particles present nanometric size (~3 nm)and have a complex crystalline structure. High intensities UV photoluminescence, shiftedtowards higher energies compared to bulk GaN, are recorded for these materials, in agreementwith quantum confinement effect. The lack of visible emission demonstrate the preparation ofdefect-free material. Then, the focus is brought to the preparation of the solid solution InxGa1-xN (0 ≤ x≤ 1) with a different approach. The reaction of a metal source with a nitrogen sourceis studied. Reactions between metal cupferronates and HMDS are deeply investigated after abrief exploratory chemistry work. An intimate mixing of both metals with a homogeneousdistribution is demonstrated for the entire solid solution and is validated with the opticalproperties. A continuous decrease of the energy maximum with increasing indium content (upto 40 % in indium) is in agreement with the theoretical values, yielding to luminescence fromUV to red.

Quantum dots exhibit strongly size-dependent optical and electrical properties. The ability to join the dots into complex assemblies creates many opportunities for scientific discovery. This motivated our present research work on QDIPs, DWELLs, and graphene like QDs. The intention of this research was to study the size dependent achievements of QDIPs, DWELLs, and graphene like QDs with those of competitive technologies, with the emphasis on the material properties, device structure, and their impact on the device performance. In this dissertation four research studies pertaining to optical properties of quantum dot and dot-in-a-well infrared photodetectors, I-V characteristics of graphene quantum dots, and energy and spin texture of germanene quantum dots are presented. Improving self-assembled QD is a key issue in the increasing the absorption and improving the performance. In the present research work, an ideal self-assembled QD structure is analyzed theoretically with twenty-hole levels (Intraband optical transitions within the valence band) and twenty-electron energy levels (DWELL). Continuing the efforts to study self-assembled QDs we extended our work to graphene like quantum dots (graphene and germanene) to study the electronic transport properties. We study numerically the intraband optical transitions within the valence band of InxGa1-xAs/GaAs pyramidal quantum dots. We analyze the possibility of tuning of corresponding absorption spectra by varying the size and composition of the dots. Both ‘x ’ and the size of the quantum dot base are varied. We have found that the absorption spectra of such quantum dots are more sensitive to the in-plane incident light. We present numerically obtained absorption optical spectra of n-doped InAs/In0.15Ga0.85As/GaAs quantum dot-in-a-well systems. The absorption spectra are mainly determined by the size of the quantum dot and have weak dependence on the thickness of the quantum well and position of the dot in a well. The dot-in-a-well system is sensitive to both in-plane and out-of-plane polarizations of the incident light with much stronger absorption intensities for the in-plane-polarized light. We also present theoretically obtained I-V characteristics of graphene quantum dots, which are realized as a small piece of monolayer graphene. We describe graphene within the nearest-neighbor tight-binding model. The current versus the bias voltage has typical step-like shape, which is due to discrete energy spectrum of the quantum dot. The current through the dot system also depends on the position of the electrodes relative to the quantum dot. In relation to graphene quantum dots, we present our study of buckled graphene-like materials, like germanene and silicene. We consider theoretically germanene quantum dot, consisting of 13, 27, and 35 germanium atoms. Due to strong spin-orbit interaction and buckled structure of the germanene layer, the direction of the spin of an electron in the quantum dot depends on both the electron energy and external perpendicular electric field. With variation of energy, the direction of spin changes by approximately 4.50. Application of external electric field results in rotation of electron spin by approximately 0.50, where the direction of rotation depends on the electron energy.

Experimental investigations of the optical properties of InGaN/GaN quantum dots are presented. A pulsed laser is used to perform time-integrated and time-resolved microphotoluminescence, photoluminescence excitation, and polarisation-resolved spectroscopy of single InGaN quantum dots under a non-linear excitation regime. The first micro-photoluminescence results from InGaN/GaN quantum dots grown on a non-polar crystal plane (11^-<sub style='position: relative;left: -.4em;'>2</sub>0) are presented. Time-resolved studies reveal an order of magnitude increase in the oscillator strength of the exciton transition when compared to InGaN quantum dots grown on the polar (0001) plane, suggesting a significantly reduced internal electric field in non-polar InGaN quantum dots. Polarisation resolved spectroscopy of non-polar InGaN quantum dots reveals 100% linearly polarised emission for many quantum dots. For quantum dot emissions with a polarisation degree less than unity, a fine structure splitting between two orthogonal polarisation axes can be resolved in an optical setup with a simple top-down excitation geometry. A statistical investigation into the origins of spectral diffusion in polar InGaN quantum dots is presented, and spectral diffusion is attributed to charge carriers trapped at threading dislocations, and itinerant and trapped carriers in the underlying quantum well layer which forms during the growth procedure. Incorporating quantum dots into the intrinsic region of a p-i-n diode structure and applying a reverse bias is suggested as a method to reduce spectral diffusion. Coherent control of the excited state exciton in a non-polar InGaN quantum dot is experimentally demonstrated by observation of Rabi rotation between the excited state exciton and the crystal ground state. The exciton ground state photoluminescence is used as an indirect measurement of the excited state population.

Three non-peripherally substituted liquid crystalline bisphthalocyanine (Pc) compounds have been studied to examine the role of central metal ions lutetium (Lu), and gadolinium (Gd) and substituent chain lengths, i.e. octyl (C8H17) and hexyl (C6H13), in determining the physical properties. For the octyl substituted Pc molecules, the head-to-tail or Jaggregates within the as-deposited spun films produced a redshift of the optical absorption Q bands in relation to their 0.01 mgml-1 solutions. Annealing at 80˚C produced a well-ordered discotic liquid crystalline (LC) mesophase causing additional redshifts irrespective of the metal ion in case of C8LuPc2 and C8GdPc2. Formation of face-to-face or H-aggregated monomers led to blueshifts of the Q bands with respect to solution spectra for C6GdPc2, both as-deposited and annealed films. Stretching and bending vibrations of pyrrole, isoindole, and metal-nitrogen bonds in Pc rings showed Raman bands at higher energy for smaller metal ion. However, no change was observed for the difference in chain lengths. As-deposited C8LuPc2 and C6GdPc2 produced comparable Ohmic conductivity, of the value 67.55 Scm-1 and 42.31 Scm-1, respectively. C8GdPc2 exhibited two orders of magnitude less conductivity than the other two due to the size effect of the central ion and side chain length. On annealing, an increase of Ohmic conductivity was noticed in the isostructural octyl substituted phthalocyanines on contrary to a reduced conductivity in hexyl substituted one. An optical band shift of the C8LuPc2 and C8GdPc2 thin films occurred on oxidation by bromine vapour. Oxidations of Pc-coated ITO were also achieved by applying potential at 0.88 V and 0.96 V electrochemically for the C8LuPc2 and C8GdPc2 compounds, respectively. To explore the applications of these compounds in biosensing, in situ interaction studies between bromine oxidised compounds and biological cofactors nicotinamide adenine dinucleotide (NADH) and L-ascorbic acid (vitamin C) were carried out using optical absorption spectroscopy. Thin films of a non-peripherally octyl substituted LC lead phthalocyanine was exposed to 99.9 % pure hydrogen sulfide gas to produce hybrid nanocomposites consisting of lead sulphide quantum dots embedded in the analogous metal free phthalocyanine matrix. Trapping of charge carriers caused hysteresis in the current-voltage characteristics of the film on interdigitated gold electrodes. The charge hopping distance was found to be 9.05 nm, more than the percolation limit and responsible for forming two well-defined conducting states with potential application as a memristor.

Molecular beam epitaxy (MBE) grown metal has been a renewed area of interest recently in order to achieve high quality metal films or nanostructures for plasmonics. Recently MBE grown silver films have been shown to possess optical constants closer to that of intrinsic silver leading to lower losses and thus allowing for higher quality plasmonics. MBE has also been used to grow silver nanocrystals and indium droplets, or islands, for plasmonics. These self-assembled nanostructures can be grown in close proximity to quantum confined structures such as InAs/GaAs quantum dots or InGaAs/GaAs quantum wells in a single process, without post-processing and fabrication, allowing for increased plasmonic enhancement due to the improved interface between the semiconductor and plasmonic structures.In this dissertation, widely tunable plasmonic resonances of indium islands will be discussed and plasmonic enhancement results will be presented and compared to those of nanoantennas constructed from standard fabrication processes. The coupling between near-surface quantum confined structures, both fabricated and self-assembled, will be compared to the coupling in typical dielectric cavities, such as photonic crystal nanobeams. Beyond the plasmonic possibilities of indium islands, indium becomes superconducting at 3.4 K. With the proximity effect allowing for electrons in materials in contact with a superconductor to occupy a superconducting like state, allowing for the possibility for a hybrid superconductor/semiconductor optical source. The observation of superconductivity in indium islands will be presented and considerations for a superconductor/semiconductor source will be discussed.

Semiconductor quantum dots (QDs), particles several nanometers in diameter, exhibit a range of interesting properties that arise as a result of quantum confinement. Among these characteristics is photoluminescence, and unlike traditional fluorophores, the fluorescence emission of QDs is characterized by broad absorption and narrow emission that is a function of the particle diameter. This allows high spatial resolution to be achieved using spectral discrimination of closely spaced QDs.We propose applying QD fluorescence as a tool to sense the local environment of the QD to achieve wide-field sensing at high-resolution. Many factors influence QD fluorescence from the growth parameters and choice of ligand to the local environment of the QD post-fabrication. Nano-materials in the local QD environment influence the spectral or temporal characteristics of the QD fluorescence and detecting these changes enables identification of the location and motion of these nanoparticles with resolution on the order of a few nanometers.We have fabricated aqueous colloidal cadmium telluride QDs, experimenting with the choice of thiol-based ligand to influence the chemistry in post-processing and application. A wide range of tools have been used to characterize the spectral and physical properties of the QDs. We have successfully immobilized QDs on a variety of substrates including glass coverslips, silicon and indium tin oxide coated glass. Immobilization is achieved with even and consistent distributions of QDs on the substrate by using self-assembly of the colloidal particles onto substrates functionalized with N1-(3-Trimethoxysilylpropyl)diethylenetriamine (DETA) silane.Using fluorescence microscopy we have successfully demonstrated the detection of interactions between QDs and other nano-materials including green fluorescent protein and gold seed particles, demonstrating that QDs may, in principle, be used in a wide field microscopy technique to sense nano-materials with high resolution.

In this thesis investigations into chemically modified graphene structures are presented. Chemical functionalization of graphene is the chemical attachment of molecules or atoms to the graphene surface via covalent or Van der Waals bonds, this process offers a unique way to tailor the properties of graphene to make it useful for a wide range of device applications. One type of chemical functionalization presented in this thesis is fluorination of graphene which is the covalent attachment of fluorine to the carbon atoms of graphene and the resultant material is fluorographene which is a wide band-gap semiconductor. For low fluorine coverage the low temperature electron transport is through localized states due to the presence of disorder induced sub-gap states. For high fluorine coverage the electron transport can be explained by a lightly doped semiconductor model where transport is through thermal activation across an energy gap between an impurity and conduction bands. On the other hand, at low temperatures the disorder induced sub-gap density of states dominates the electrical properties, and the conduction takes place via hopping through these localized states. In this thesis it is also shown that electron beam irradiation can be used to tune the coverage of fluorine adatoms and therefore control energy gap between the impurity and conduction bands. Futhermore, electron beam irradiation also offers a valuable way to pattern conductive structures in fluorinated graphene \textit{via} the irradiation-induced dissociation of fluorine from the fluorinated graphene. This technique can be extended to the patterning of semiconducting nano-ribbons in fluorinated graphene where the spatial localization of electrons is just a few nm. The second type of chemical functionalization presented in this thesis is the intercalation of few layer graphene with ferric chloride which greatly enhances the electrical conductivity of few layer graphene materials making them the best known transparent conductors.

This thesis is an investigation of infrared electro-absorption at room temperature in electrochemically self assembled Cadmium Sulfide quantum dots produced by electrodepositing the semiconductor in 50nm pores of an anodic alumina film. Infrared absorption in these systems is associated with real space transitions of electrons between electronic states in the Cadmium Sulfide quantum dots and trap states in the surrounding alumina. When an electric field is applied on a quantum dot, it modulates the absorption by altering the overlap between the wavefunctions of dot states and the trap states in the alumina. This results in a change in the matrix element for absorption. Such a phenomenon is reminiscent of the quantum confined Stark effect. The ability to electrically modulate absorption in these structures can result in inexpensive infrared signal processing devices operating at room temperature.