Made available in DSpace on 2014-06-12T23:14:32Z (GMT). No. of bitstreams: 2 arquivo7642_1.pdf: 1977405 bytes, checksum: 9ee0b0f45dde924aa155dc2b1018f9f8 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2011 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Os organofosforados caracterizam-se como uma classe importante de pesticidas, atuando como inibidores da atividade enzimática da acetil colinesterase (AChE). Dentre os organofosforados de uso permitido no Brasil, destacamos o clorpirifós (CPF). Neste trabalho, desenvolveu-se novas metodologias para a obtenção de Qds de CdTe, em meio aquoso, utilizando-se ultrassom de alta potência para acelerar o processo de obtenção dos NCs. Em seguida, os Qds obtidos foram incorporados em hidrogéis de agarose, para avaliação do comportamento de suas propriedades espectroscópicas em diferentes concentração do polissacarídeo desta matriz. Por fim, avaliou-se a capacidade de detecção dos Qds de CdTe incorporados em hidrogéis de agarose a 0,50 %(m/v), na presença de diferentes concentrações de CPF (0.1, 0.5 e 1.0 ppm), complexados nas cavidades de moléculas de β-CD. As amostras de Qds sintetizadas foram caracterizadas estruturalmente e espectroscopicamente pelas técnicas de MET e DRX (estrutural) e Absorbância UV-vis e espectroscopia de fluorescência e excitação. As amostras incorporadas nos hidrogéis de agarose e os experimentos de detecção dos pesticidas foram caracterizados por espectroscopia de fluorescência. Os resultados obtidos mostraram a viabilidade das metodologias desenvolvidas, tanto para a obtenção dos Qds com tamanho médio abaixo de 5 nm e com boa fluorescência e fotoestabilidade, quanto para a detecção dos pesticidas em meio aquoso, comprovando que é possível o desenvolvimento de sensores baseados em Qds e ciclodextrinas, sem a necessidade de processos complicados de conjugação covalente entre estes compostos, para a aplicação na detecção de CPF em concentrações abaixo de 1 ppm, em meio aquoso

Ce travail est consacré à l’élaboration et à la caractérisation d’un nouveau matériau hybride présentant des propriétés de transfert d’énergie, à base de la protéine photochromique bactériorhodopsine (bR) acceptrice d’énergie et de boites quantiques (QDs) de CdSe/ZnS fluorescentes donneuses d’énergie. Le but est d’essayer d’améliorer et d’utiliser les propriétés photochromiques et photochimiques de la bR en utilisant un transfert d’énergie par résonancede Förster (FRET) qui peut exister avec des QDs semiconductrices. Ce nouveau matériau hybride pourrait servir dans divers domaines, tels que des commutateurs optiques ou lescellules photovoltaïques.Les propriétés physiques d’un tel composé et son efficacité dépendant fortement de sa structure, ce travail à consister à élaborer le complexe bR/QD et à le caractériser par microscopie à force atomique (AFM) et par spectrométries optiques (fluorescence,absorption) afin de mettre en évidence un éventuel effet FRET entre bR/QDs. Nous avons montré qu’en modifiant la charge de surface des QDs nous pouvions optimiser l’efficacité duFRET. Cet effet provient d’une modification des forces électrostatiques entraînant un arrangement des QDs différent à la surface des membranes en fonction de leur charge de surface. En renforçant la liaison bR/QD à l’aide de biotine et de streptavidine, nous avons atteint une efficacité maximale de FRET de 80 %.Lors de nombreuses expériences que nous avons menées, nous avons montré parAFM et dichroïsme circulaire que la présence de QDs accélère fortement le processus de monomérisation de la bR par du détergent ce qui pourrait avoir des applications en biologie. / In this work, we built and characterized a new hybrid material with energy transfer properties made from photochromic protein Bacteriorhodopsin (bR) which is the energy acceptor and CdSe/ZnS fluorescent quantum dots (QDs) which are the energy donor. Our aim was to improve the photochromic and photo-physical bR properties by using a Förster resonance energy transfer (FRET) which should exist in presence of semiconductor QDs. This new hybrid material should have applications in many fields such as optical switching or photovoltaics.Since optical properties and efficiency of such a material are highly dependent of its structure, our work was to develop and characterize bR/QD complex by atomic force microscopy (AFM) and optical spectrometries (fluorescence, absorption) in order to demonstrate FRET between bR and QDs. By tuning QDs surface charges, we proved that we were able to optimize FRET, by optimization of the electrostatic interactions between bR and QDs. This effect was due to a better organization of QDs on the membrane surface when interactions were optimized. We also showed that when QD and bR are linked by biotin streptavidin link they revealed the maximum FRET efficiency of 80 %.During all these experiments, we showed that QDs could induce a quicker detergent monomerization of bR. This is supported by AFM images and circular dichroïsm measurements. This effect should find applications in biology.

Philosophiae Doctor - PhD / The human epidermal growth factor receptor (HER)-family of receptor tyrosine kinases; human epidermal growth factor receptor 1, human epidermal growth factor receptor 2, human epidermal growth factor receptor 3 and human epidermal growth factor receptor 4 (EGFR/HER1, ErbB2/HER2, ErbB3/HER3, and ErbB4/HER4) plays a major role in the pathogenesis of many solid tumours, in approximately 25 - 30% of breast cancers. Breast cancer is the second most common type of cancer and affects around 3000 women annually in South Africa alone. While the benefits of treatment and cancer progress to enhance therapeutic effectiveness for the patient are well documented, it is also important to employ or fabricate methods in which cancer can be screened at an early stage. A number of gene and protein based biomarkers have shown potential in the early screening of cancer. One specific biomarker that is over-expressed in 20 - 30% of human breast cancers is the human epidermal growth factor receptor 2 (Her2/neu). Several methods have been developed for detection of Her2/neu oncogene including immunohistochemistry (IHC), enzyme-linked immunosorbent assay (ELISA), fluorescent in situ hybridisation (FISH) and polymerase chain reaction(PCR). However, these methods are subjected to interference problem. For these reasons an ultrasensitive, cheap and easy to use genosensor has been developed for early detection of the Her2/neu oncogene using electrochemical and spectroscopic methods. Due to their high surface-to-volume ratio, electro-catalytic activity as well as good biocompatibility and novel electron transport properties quantum dots are highly attractive materials for ultra-sensitive detection of biological macromolecules via bio-electronic or bio-optic devices. In this study a quantum dots (QDs)-based genosensor was developed in which Ga2Te3-based quantum dots were synthesised using a novel aqueous solution approach by mixing 3-mercaptopropionic acid (3MPA)-capped gallium metal precursor with reduced tellurium metal. The morphological, compositional and structural characterisation of the QDs was investigated prior to their utilization in DNA sensor construction.

The use of colloidal quantum dots (QDs) for photovoltaic energy conversion is a nascent field that has been dominated for well over a decade by the use of 3-mercaptopropionic acid (3-MPA) capped PbS QDs. These QDs are routinely deposited via an in situ solid state ligand exchange process that displaces the native oleate ligand on the PbS QD surface. This ligand exchange procedure is wasteful of material and has been demonstrated to leave numerous impurities that limit electronic performance of the as-deposited QD devices. Until the last few years there was very little understanding in chemical literature as to many important aspects of QD chemistry for this material pairing outside the framework of a QD solid. In this work, a colloidal suspension of 3-MPA capped PbS QDs in DMSO was formulated and investigated to probe ligand dynamics and optical properties of the suspended colloid. QD bound 3-MPA was found to be in dynamic exchange with "free" ligand in solution by 1H-NMR spectroscopy. Optical properties and colloidal stability were found to be heavily dependent on the presence of a significant excess of free ligand. PbS QDs were also found to be highly photo-catalytic towards oxidative dimerization of 3-MPA to its dimer, dithiodipropionic acid (dTdPA). After an initial colloidal suspension was achieved, attempts were made to directly deposit the colloid as a QD "ink" to form optoelectronic devices. While photo-switchable devices were obtained, ultimately it was determined that DMSO was a largely incompatible solvent choice for solution processing methodologies. Subsequently, 3-MPA capped PbS QD colloids were obtained in volatile organic solvents amenable to solution processing by the addition of a stabilizing ammonium salt. These QD colloids maintained excellently resolved optical properties and were able to form conformal coatings from simple evaporative deposition. The ligand chemistry of this colloid was extensively investigated via NMR and optical spectroscopy. These QDs were also found to be highly photo-catalytic towards conversion of monomer 3-MPA to dTdPA.

There is currently interest in developing control over the spin of a single Manganese (Mn) ion, the atomic limit of magnetic memory, in semiconductor quantum dots (QDs). In this work we present theoretical results showing how one can manipulate the spin of Mn ion with light in a QD by engineering Mn-multi-exciton interactions through quantum interference, design of exciton and bi-exciton states and application of the magnetic field. We develop a fully microscopic model of correlated exciton and bi-exciton interacting with the Mn ion. The electrons and heavy holes, confined in the QD, approximated as a two-dimensional harmonic oscillator (HO), interact via direct and short- and long-range exchange Coulomb interactions. The matrix elements of the exchange interaction are computed for the first time in the harmonic oscillator basis and for arbitrary magnetic fields. The exciton and bi-exciton energies and states are computed using the configuration interaction method. The interaction between carriers and the Mn spin is accounted for by the Heisenberg electron-Mn and Ising hole-Mn exchange interactions. For a single exciton confined in a magnetic dot, a novel quantum interference (QI) effect between the electron-hole Coulomb scattering and the scattering by Mn ion is obtained. The QI significantly affects the exciton-Mn coupling, modifying the splitting of the emission/absorption lines from the exciton-Mn complex depending on the degree of electronic correlations in the exciton state. The second signature of the QI are the nonuniform energy gaps between the consecutive emission peaks due to the scattering of carriers by Mn among single-particle orbitals. Magneto-photoluminescence experiments show that the coupling between the exciton and Mn ion does not change in the magnetic field. We report that electron-hole correlations counteract the magnetic squeezing of the single-particle wave functions strengthening the carrier-Mn interactions. As a result, the rate of change of the magneto-photoluminescence spectra with magnetic field is reduced as observed in the experiment. We develop here for the first time a microscopic theory of bi-exciton-Mn complex, and report the presence of the fine structure of bi-exciton-Mn complex, even though as a spin-singlet it is expected to decouple from the localized spin. Theoretical results are compared with experiments in Grenoble and Warsaw.

The environmental, microbiological and technological aspects of selenium is explored with the aim of assessing and identifying microorganisms capable of interacting with Se in the environment and forming functional 'bionanomaterials'. To determine the natural microbial response to high selenium concentrations, and to understand the role soil microorganisms play in transforming Se, a field site in Co. Meath, Ireland, was identified and sampled to determine the Se contents. Detailed examination of the soil profile showed toxic levels of Se up to 156ppm. The highest Se concentrations correlated with elevated concentrations of higher plant matter, inferring a phytoconcentration mechanism for Se within a post glacial fen, and Se was identified as a reduced organic species. Microcosm experiments were established to test whether the soil microbial community displayed increased resistance to Se. These revealed the Se present in the soil was recalcitrant to microbial degradation and Se(VI) enriched experiments were noted to cause drastic alterations in community structure, indicating elevated Se resistance was not widespread throughout the community. Despite this, amended Se(VI) was rapidly reduced to Se(0), as determined by XAS. Selenium, and the group 16 element tellurium, also display physico-chemical properties that make them ideal for a range of industrial, chemical and technological applications, including sequestration of hazardous wastes and as metal chalcogenide semiconducting 'quantum dots'. Se(0) and Te(0) bionanomaterials formed by 'resting cell' cultures of the model environmental isolate Geobacter sulfurreducens, despite low MIC values, were characterised and subsequently applied to the sequestration of Hg(0)v derived from Hg historically used to preserve herbarium specimens. This showed that the Hg can be sequestered by the Se(0) bionanoparticles in the form of HgSe and demonstrated increased stability over abiotic counterparts. Finally, the bacteria G. sulfurreducens, Shewanella oneidensis and Veillonella atypica were compared for Se(IV) reducing capabilities, and V. atypica was shown to be adept at the production of significant quantities of Se(II-) utilising the electron shuttle AQDS. Biogenic Se(II-) compared favourably with abiotic Se(II-) solutions in the formation of metal selenide quantum dots, displaying increased particle growth control as shown via a novel, time resolved XAS technique. Bacterial polymeric substances are inferred in controlling Se(II-) precursor stability. This research shows that bacteria represent an alternative, facile, 'green' synthetic method for the production of next-generation technological nanomaterials.

In this thesis time-resolved photoluminescence spectroscopyis presented as a powerful tool to study the carrier dynamicsin various self-assembled quantum dot (QD) structures, whichare potentially attractive for device applications. The experiments reveal the impact of proton irradiation onInGaAs QDs and comparable quantum wells. Nonradiativerecombination at defects–an important material parameterand“measure”of the structure optical quality–is found to play a much less important role for the QD samples.The superior radiation hardness can be explained as a result ofthe three-dimensional carrier confinement in QDs. Comparisonsbetween the structures show a decrease of photoluminescenceintensity for quantum wells but a slight increase for QDsirradiated at low to intermediate doses. This somewhatunexpected characteristic is described by an enhanced carriertransfer into the dots via the defects introduced in thematerial by the protons. In a different structure carrier dynamics in spatiallyaligned of InAs QDs are investigated. Alignment along lines isachieved by misfit dislocations deliberately introduced in thesubstrate. Photoluminescence spectra of the dots exhibit muchsmaller inhomogeneous broadening than for the reference sampleas a result of an improved QD uniformity. Samples with varyingbuffer layer thicknesses were grown to study the influence ofdislocation related traps on the observed fastphotoluminescence decay. It is found that the fast carriertrapping is predominantly caused by point defects close to theQDs or at the QD/barrier interfaces. Additional numerical simulations confirm the roles of thetwo independently acting traps in nonradiativerecombination.

Doctor Scientiae - DSc / Semiconductor nanocrystals or quantum dots (QDs) are fluorescent nanometer-sized particles which have physical dimensions that are smaller than the excitonic Bohr radius, large surface area-to-volume ratios, broad absorption spectra and very large molar extinction coefficients. Biomedical applications of QDs are mainly based on II-VI QDs containing cadmium, such as CdSe/ZnS. These cadmium-based systems are associated with high toxicity due to cadmium. As a result, potential replacements of cadmium-based QDs in biological applications are needed. In this study, InP/ZnSe QDs were synthesized for the first time using a one-pot hot injection method. Furthermore, a growth-doping method was used for silver, cobalt and iron incorporation into the InP core. Water compatibility was achieved through ligand exchange with 3- mercaptopropionic acid. In vitro cytotoxicity and imaging/internalization of the as-prepared MP A-InP/ZnSe and MP A-capped CdTe/ZnS QDs were evaluated. InP/ZnSe QDs were successfully synthesized with ZnSe shell causing a 1.4 times reduction in trap-related emission.

Studie- och yrkesvägledning i skolan framställs på flera olika sätt. Ibland verkar det vara en engångsföreteelse, vägledning innan ett viktigt val, såsom gymnasievalet. Andra gånger pratas det om vägledning som en kontinuerlig process som pågår under flera år. Med nya bestämmelser om obligatorisk prao i årskurs åtta och nio är det intressant att undersöka effekten den har på elevers karriärkompetens och karriärlärande. Utifrån tesen att vägledning, på det ena eller andra sättet leder till karriärlärande undersöks studie och yrkesvägledares perspektiv på huruvida prao eller andra jämförbara aktiviteter i skolans värld leder till karriärlärande.Syftet med uppsatsen är att undersöka huruvida elever får till sig karriärlärandegenom prao samt jämförbara aktiviteter i den svenska skolan. Uppsatsens empiriska data utgår ifrån studie - och yrkesvägledares perspektiv. Frågeställningarna som besvaras är följande:Hur skulle ungdomar genom prao samt övriga arbetslivsorienterande aktiviteter kunna få till sig karriärlärande utifrån DOTS modellen? När bör ett arbete med karriärlärande starta?I resultatet och diskussionen framkommer att prao bör integreras mer iundervisningen. I dagsläget finns det, enligt svaren från informanterna, få tydliga riktlinjer för ett sådant arbete. Genom att reflektera samt utvärdera upplevelser på arbetslivsorienterandeaktiviteter tillåts elever att dra paralleller mellan det akademiska innehållet och praktikens arbetsuppgifter. De tre främsta kunskaperna eleverna får till sig genom arbetslivsorienterande aktiviteter är en ökad självkännedom, kunskap kring arbetslivet, ett ansvarstagande samt den generella erfarenheten av att komma ut på arbetsplatser. Aktiviteter direkt kopplade till arbetslivet underlättar övergången mellan skola och arbetsliv och ett arbete med karriärlärande bör starta som ett komplement i utbildningen i god tid och inte enbart strax inpå ett val.

Magister Scientiae (Medical Bioscience) - MSc(MBS) / Nanotechnology is a rapidly expanding field with a multitude of practical uses namely textiles, cosmetics, agriculture, and health sciences. The focus, for the purposes of this thesis, will be on carbon dots. The small size and low surface-to-volume ratio result in different physico-chemical behaviour of these particles in comparison to its significantly larger bulk-produced counterparts.