<p>I. Gallium-hemoglobin Coated Silver Nanoparticles for Antimicrobial Photodynamic Therapy Against Bacterial Pathogens One of the mechanisms for bacterial pathogens’ hemin acquisition is through cell-surface hemin receptors (CSHRs), which are responsible for rapid hemin recognition. GaPpIX, as a hemin analog, can be rapidly taken up by CSHR-expressing bacteria, such as <i>Staphylococcus aureus</i> (<i>S.aureus)</i>. Previous works shown that GaPpIX has aPDI activity at micromolar level of concentration following 10 seconds of 405-nm light exposure using LED array. The photosensitizing ability of GaPpIX can be further enhanced by incorporating with hemoglobin (GaHb) and 10 nm silver nanoparticles (AgNP). The results suggested a higher aPDI activity of GaHb-AgNP than any of its components against MRSA strains and neglectable cytotoxicity against keratinocytes. GaHb-AgNPs were also found having aPDI activity against intracellular MRSA and <i>Mycobacterium abscessus </i>but not effective against <i>S. aureus</i> biofilm. GaHb-AgNPs have no significant toxicity toward macrophages with concentrations lower than 22.64 μg/mL.</p> <p> </p> <p>II. Synthesis and Properties of Magnetic Gold Nanoparticles</p> <p> Superparamagnetic gold nanoparticles support hybrid magnetic and plasmonic properties that can be exploited for a variety of applications. In this paper we present new insights on the synthesis of magnetic gold nanoparticles (MGNPs) with an emphasis on efficiency, scalability, and waste reduction, supported by a comprehensive analysis of their physical and materials properties. Aqueous suspensions of colloidal Fe₃O₄ are conditioned with 5-kDa polyethylene glycol and L-histidine to mediate the nucleation and growth of gold by a mild reducing agent. Isotropic MGNPs on the order of 100 nm can be synthesized using scalable reaction conditions with Au:Fe mole ratios as low as 1:2 and cleansed with generally regarded as safe (GRAS) chemicals for the removal of residual iron oxide. High-resolution energy-dispersive x-ray imaging of individual MGNCs revealed these to be ultrafine composites of gold and SPIO rather than core–shell structures. The attenuated total reflectance infrared (ATR-IR) spectroscopy and Raman spectroscopy indicated that the cleansing step does change the optical properties of the synthesized MGNPs. Magnetometry of MGNCs in bulk powder form confirmed their superparamagnetic nature, with bulk moments between 6 to 7 emu/g.</p>

Esse trabalho teve como objetivo a produção e a caracterização elétrica de filmes finos de telureto com nanopartículas de ouro, depositados pela técnica sputtering, para aplicação em dispositivos de memória. Os filmes finos foram produzidos a partir de alvos cerâmicos de telureto (TeO2-ZnO) e foram nucleadas nanopartículas de ouro para observar sua influência no comportamento de memória. Foi desenvolvida metodologia adequada para a nucleação das nanopartículas por meio de tratamento térmico. Foram produzidos filmes com diferentes concentrações e tamanhos de nanopartículas e diferentes fluxos de oxigênio durante a deposição. Os filmes foram caracterizados por técnicas como Microscopia Eletrônica de Transmissão (TEM), Perfilometria, Espectrometria por Retroespalhamento de Rutherford (RBS) e extração de curvas de Corrente x Tensão (I-V). Por meio das medidas I-V foi possível identificar as melhores condições para aplicações em memória e correlacioná-las com as variáveis de processo estudadas. Resultados obtidos mostraram que a melhor condição para aplicações em memória não volátil foi encontrada em filmes com 100 nm de espessura e depositados com fluxo de oxigênio de 1 sccm, abertura do shutter em 50 e tratados termicamente por 10 ou 20 horas à 325 ºC. Nesses casos, foi observado um abrupto aumento na corrente (4 ordens de grandeza) em aproximadamente 6,5 V para 10 horas de tratamento térmico e 3,5 V para 20 horas de tratamento térmico, indicando a transição do estado inicial de baixa condutividade para outro de alta condutividade. As nanopartículas de ouro proporcionam maior capacidade de armazenamento de elétrons e não favorecem o transporte de corrente através do isolante; elas atuam como armadilhas para as cargas elétricas, o que reduz a corrente de fuga para níveis mais baixos. Foi estudada a influência do diâmetro e da concentração volumétrica das nanopartículas de ouro no valor da tensão elétrica associada à transição abrupta da corrente. Este parâmetro desempenha um papel importante no efeito de memória, pois determina a facilidade/dificuldade em se preencher e saturar as armadilhas (nanopartículas de ouro) com elétrons. Os materiais estudados neste trabalho mostraram-se promissores para aplicações em dispositivos de memória não volátil e possuem características semelhantes aos materiais orgânicos usados para o referido fim. / This work has the objective to fabricate and characterize electrically tellurite thin films containing gold nanoparticles, deposited by the sputtering technique, for application in memory devices. Thin films were produced from ceramic tellurite targets and gold nanoparticles were nucleated in order to observe their influence on memory behavior. An appropriate method was developed for the nucleation of the nanoparticles by means of heat treatment. Films with different nanoparticles sizes and concentration and different oxygen fluxes during the deposition, were produced. The films were characterized by techniques such as Transmission Electron Microscopy (TEM), Profilometry, Rutherford Backscatter Spectrometry (RBS) and current x voltage (I-V) curves. Using I-V measurements, it was possible to identify the best conditions for memory applications and correlate them with the process variables studied. The results showed that the best condition for memory applications was found in films with 100 nm thickness and deposited with oxygen flow of 1 sccm, opening shutter in 50 and heat treated for 10 or 20 hours at 325 ºC. In these cases, current abrupt increase (4 orders of magnitude) was observed at about 6.5 V for 10 hours of heat treatment and 3.5 V for 20 hours of heat treatment, indicating the transition from high impedance state to low impedance state. Gold nanoparticles provide a larger electron storage capability, and do not favor the electric transport through the insulator; they act as traps for electrical charges, which reduces the leak current to lower levels. It was studied the influence of the gold nanoparticles diameter and volumetric concentration on the voltage associated to the abrupt current. These parameters played an important role in the memory effect, as they determined the facility/difficulty to fill and saturate the traps (Au nanoparticles) with electrons. The materials studied in the present work, based on TeO2-ZnO thin films with Au nanoparticles, are promising for applications in nonvolatile memory device with similar characteristics to organic materials used for the same purpose.

Nanofibras poliméricas obtidas por eletrofiação possuem alta relação superfície-volume, e podem ser recobertas com nanomateriais que interajam com os grupos funcionais dos polímeros. Neste trabalho, nanofibras de poliamida 6/polialilamina hidroclorada (PA6/PAH) com diâmetro da ordem de 100 nm e sem defeitos foram recobertas com nanotubos de carbono (CNTs) e nanopartículas de ouro (AuNps) para produzir sensores e biossensores. A versatilidade da plataforma com as nanofibras foi demonstrada com três aplicações distintas. A adsorção de CNTs sobre as nanofibras permitiu a detecção do neurotransmissor dopamina com medidas de voltametria de pulso diferencial com sensibilidade na faixa de 1 a 70 &mu;mol.L-1 e limite de detecção de 0,15 &mu;mol.L-1, sem interferência do ácido úrico e ácido ascórbico. Nos imunossensores para detectar o antígeno CA 19-9, biomarcador para câncer de pâncreas, as nanofibras de PA6/PAH recobertas com CNTs ou AuNPs receberam camada adicional do anticorpo anti-CA 19-9. Usando medidas de espectroscopia de impedância eletroquímica, esses imunossensores puderam detectar CA 19-9 em tampão e em soro de sangue de pacientes de câncer com diferentes probabilidades de desenvolver câncer de pâncreas. A seletividade dos imunossensores também foi testada com possíveis interferentes no sangue. Na terceira aplicação, obteve-se sinergia com a codeposição de CNTs e AuNPs sobre as nanofibras para a formação de um biossensor contendo uma camada da enzima tirosinase. Imagens de microscopia eletrônica mostraram uma estrutura 3D interconectada, formada pelas nanofibras de PA6/PAH, AuNPS e CNTs. O biossensor foi usado para detectar bisfenol A com cronoamperometria na faixa de 0,05 a 1,1 &mu;mol.L-1 e limite de detecção de 8 nmol.L-1. Conclui-se que nanofibras poliméricas constituem excelente plataforma para sensores e biossensores pela possibilidade de incorporação de outros nanomateriais para aplicações específicas. / Electrospun polymer nanofibers have a high surface-volume ratio, and can be coated with nanomaterials that interact with the functional groups of the polymers. In this work, defect-free nanofibers of polyamide 6/polyallylamine hydrochloride (PA6/PAH) with a diameter of ca. 100 nm were coated with carbon nanotubes (CNTs) and gold nanoparticles (AuNps) to produce sensors and biosensors. The versatility of the platform with nanofibers has been demonstrated with three distinct applications. The adsorption of CNTs on the nanofibers allowed the detection of the neurotransmitter dopamine with differential pulse voltammetry measurements with sensitivity in the range of 1 to 70 &mu;mol.L-1 and detection limit of 0.15 &mu;mol.L-1, without interference of uric acid and ascorbic acid. In the immunosensors to detect CA 19-9 antigen, biomarker for pancreatic cancer, PA6/PAH nanofibers coated with CNTs or gold nanoparticles (AuNPs) received an additional layer of anti-CA 19-9 antibody. Using electrochemical impedance spectroscopy measurements, these immunosensors were able to detect CA 19-9 in buffer and in blood serum from cancer patients with different probabilities of developing pancreatic cancer. The selectivity of the immunosensors was also tested with possible interferents in the blood. In the third application, synergy was obtained with co-deposition of CNTs and AuNPs on the nanofibers for the formation of a biosensor containing a layer of the enzyme tyrosinase. Electron microscopy images showed an interconnected 3D structure, formed by PA6/PAH nanofibers, AuNPS and CNTs. The biosensor was used to detect bisphenol A with chronoamperometry in the range of 0.05 to 1.1 &mu;mol.L-1 and detection limit of 8 nmol.L-1. It is concluded that polymer nanofibers are an excellent platform for sensors and biosensors because of the possible incorporation of other nanomaterials for specific applications.

Ligand-stabilized metal nanoparticles (LSNPs) have garnered significant attention for use in applications including sensing, catalysis, and thin film fabrication. Many uses rely on the size-dependent properties of the metal nanoparticle core. Therefore, preservation of nanoparticle core size is of paramount importance. In other uses, the low processing temperatures afforded by metal LSNPs make them attractive as precursors for conductive thin films. In these distinctly different applications, understanding nanoparticle thermal stability is crucial. A key finding of this research is that nanoparticle sintering is dependent upon both core size and ligand functionality. Multi-technique analysis of four types of gold nanoparticles (AuNPs) with different ligand compositions and core sizes illustrates that more volatile ligands reduce the onset temperature for sintering. Also, AuNPs of larger core size with the same ligand composition exhibit lower sintering onset temperatures. Correlation between measurements reveals that only a small amount of ligand loss is necessary to trigger rapid sintering and that ligands are excluded to the surface of the porous gold films. AuNPs with ligand shells composed of two alkanethiols of different chain length and volatility indicate that the onset temperature of sintering can be tuned further through incorporation of a small amount of more volatile alkanethiol into a ligand shell of lower volatility. Mixed LSNPs further reveal that AuNP thermal stability depends upon the ligand shell composition and its intermolecular interactions, which can result in markedly different sintering behavior for different ligand compositions. Long-chain alkanethiol AuNPs sinter after only a small amount of ligand loss, whereas short-chain alkanethiol AuNPs sinter following complete ligand loss and the formation of metastable bare AuNPs. Heated AuNP films prepared with mixed-ligand AuNPs exhibit ligand-dependent differences in film morphology. To probe AuNP thermal stability in 2D-assemblies, self-assembly using larger ‘marker’ nanoparticles enables the study of small 1.5 nm AuNP arrays with successive TEM monitoring throughout ex situ heating. Monitoring images of the same area shows short-range (1-2 nm) nanoparticle migration/coalescence. In contrast to 3D assemblies, AuNP growth occurs at temperatures as low as 60 °C. This dissertation includes previously published and unpublished co-authored material. / 10000-01-01

Aplicações de nanomateriais em biossensores têm recebido muito interesse nos últimos anos. Entre os vários tipos de biossensores estudados, sensores de glicose têm recebido destaque devido a sua importância em diagnósticos clínicos. Apesar do grande avanço no monitoramento de glicose nas últimas décadas, ainda há muitos desafios para alcançar um monitoramento de glicemia continuo, clinicamente preciso, em conexão a um sistema fechado otimizado para a entrega de insulina no corpo. Esta dissertação descreve a fabricação de filmes layer-by-layer (LbL) obtidos a partir da enzima glicose oxidase (GOx) e dos polieletrólitos poli(amidoamina) de geração 4 (PG4) e o hibrido PG4 com as nanopartículas de ouro (PG4AuNp). As nanopartículas de ouro foram sintetizadas em meio aquoso usando o dendrímero PG4, o ácido cloroáurico (HAuCl&#8324;4) e ácido fórmico. As medidas de espectroscopia UV-Vis dos filmes automontados em substratos de quartzo mostraram um crescimento linear em função do número de bicamadas depositados apenas para o filme PG4-GOx. No filme PG4AuNp-GOx o crescimento não é linear. Em adição às caracterizações ópticas, estrutural e eletroquímica, os filmes LbL, depositados sobre substratos de vidro recoberto com óxido de índio (ITO) foram testados para a atuação em biossensores de peróxido de hidrogênio e de glicose. A biofuncionalidade da GOx e a viabilidade do método como biossensor foi demonstrada pelo aumento da corrente em função das sucessivas adições de alíquotas de glicose à solução. Os filmes sem nanopartículas não foram sensíveis a glicose. O biossensor com melhor desempenho foi o ITO-(PG4AuNp-GOx) com 5 bicamadas, que mostrou-se linear na faixa de 0 a 4,8 mM de glicose com sensibilidade 0,013 &mu;A/mM e limite de detecção 0,44 mmolL &sup1;. / Applications of nanomaterials for biosensors have been target of substantial research in the last years. Among a large number of biosensors, glucose biosensors have attracted attention due to their applications in clinical diagnostics. Despite the remarkable progress in glucose biosensors in the last decades, there are still many challenges in achieving clinically accurate continuous glycemic monitoring in connection to closed-loop systems aimed at optimal insulin delivery. This dissertation describes the fabrication of layer-by-layer (LbL) films obtained from the enzyme glucose oxidase (GOx) and the polyelectrolytes poli(amidoamine) generation 4 (PG4) and PG4 containing gold nanoparticles (PG4AuNp). Gold nanoparticles were synthesized in aqueous solution using formic acid, PG4 and HAuCl &#8324;. UV-vis spectroscopy showed a linear growth on quartz substrate only in the system PG4-GOx. In addition to the optical, structural and electrochemistry investigation, these LbL films deposited on ITO-coated glass were employed as electrochemical glucose biosensors. The biofunctionality of GOx and feasibility of the method as biosensor are demonstrated by the increase of reduction current upon additions of successive aliquots of glucose. The biosensor ITO-(PG4AuNp-GOx) &#8325; with the optimum performance had a detection limit of 0.44 mmolL&sup1; with a linear response in the range from 0 to 4.8 mmolL&sup1; and sensibility 0.013&mu;A/mmolL &sup1;.

O ranelato de estrôncio é uma droga encontrada nas farmácias com o nome de Protos&#174;, sendo bastante consumida na forma de chás para o tratamento da osteosporose, uma patologia do tecido ósseo ligada ao metabolismo de reabsorção óssea e a produção de osteoblastos (células precursoras da matriz óssea). Sua estrutura inusitada apresenta um anel tiofeno com quatro grupos carboxílicos e um grupo nitrila, lembrando o complexante clássico EDTA. Essa semelhança inspirou o desenvolvimento desta tese, visando entender a química do íon ranelato na presença do estrôncio e outros íons metálicos, e dessa forma, obter indícios de como pode atuar ao nível molecular no organismo. Com esse objetivo, a molécula foi criteriosamente estudada baseada em espectroscopia (RMN, FTIR, Raman, EDX e Vis-UV), difração de raiosX de pó, espectrometria de massa, e modelagem molecular (MM+, ZINDO/S, DFT, TD-DFT). Ao longo do trabalho, observou-se que em meio ácido, sob exposição direta ao sol ou irradiação UV, havia a formação de uma coloração azul intensa, chamando a atenção para uma nova espécie, ainda não reportada na literatura. Esse produto mostrou ser bastante estável, particularmente sob luz solar, contrastando com a maioria dos corantes orgânicos convencionais. Os espectros de RMN e de massa indicaram a formação de um novo corante bistiofeno, envolvendo o desprendimento fotoquímico de CO2 via descarboxilação do grupo ligado ao carbono 5 do anel, seguido pela dimerização. Por outro lado, na presença de íons de ouro(III), o ranelato reage rapidamente produzindo suspensões vermelhas de nanopartículas de ouro, que permanecem estáveis por longo tempo, especialmente no caso dos sais de sódio e lítio. As reações ocorrem espontaneamente à temperatura ambiente, e a cinética foi investigada espectrofotometricamente variando a proporção ouro/ranelato (em mol) de 8:1 a 1:8. As partículas formadas foram monitoradas por microscopia eletrônica de transmissão de alta resolução. Por analogia com o método de Turkevich, a reação parece envolver a oxidação do íon ranelato por AuIII, produzindo compostos com AuI e convertendo o grupo carboxilato em CO2. É possível que o AuI permaneça ligado covalentemente ao anel tiofeno, coordenando-se pelo átomo de carbono 5. Nessa forma, o composto pode iniciar a nucleação das nanopartículas por meio de reações redox sucessivas com as espécies AuIII existentes, e desproporcionamento de AuI em Au0 e AuIII. Em condições próximas da equimolar são formadas partículas esféricas, enquanto que com excesso de AuIII, partículas anisotrópicas foram observadas. No presente estágio, a química do íon ranelato ainda é muito incipiente, mas já é possível vislumbrar sua exploração em diversas áreas da química, indústria de corantes além de novas aplicações medicinais. / Strontium ranelate is a drug commercially available in Brazil as Protos&#174;. It is widely consumed as tea infusions for the treatment of osteosporosis, a disease of the bone tissues related to the bone resorption and osteoblast replication. Its peculiar structure is composed by a central thiophene ring, exhibiting four carboxylate groups and a nitrile moiety, resembling the classical metal chelating agent EDTA. Such analogy inspired the present thesis, aiming the understanding of its chemistry in the presence of metal ions such as lithium, sodium and strontium, and expecting to provide some clues for its action in the organism. In this way, the molecule was extensively studied based on spectroscopy (NMR, FTIR, Raman, EDX and VisUV), powder X-ray diffraction, mass spectrometry, and molecular modeling methods (MM+, ZINDO/S, DFT and TD-DFT). In acidic solution, under direct solar or UV irradiation, a deep blue color was observed, calling our attention for its conversion into a new species not yet reported in the literature. This product was remarkably stable, particularly to sun light, in contrast to most conventional dyes. Our research based on NMR and mass spectra indicated the formation of a new bisthiophene dye, by the photochemical release of the carboxylate group bound at the C5 atom of the ring, followed by dimerization. On the other hand, in the presence of gold(III) ions, ranelate reacts rapidly yielding red nanoparticle suspensions which remain stable in the case of its sodium and lithium salts, but turning into blue and precipitating in the case of the strontium species. The reactions proceed spontaneously at room temperature and the kinetics were investigated spectrophotometrically by varying the ranelate/gold molar ratio from 8:1 to 1:8, and monitoring the generated nanoparticles by HRTEM. By analogy with the citrate method developed by Turkevich, the reaction seems to involve the oxidation of the ranelate ion by AuIII, yielding AuI species and converting carboxylate group into CO2. Presumably, the AuI ion remains covalently attached to the thiophene ring by coordinating to the C5 atom. In this way it can act as a nucleation center for the formation of nanoparticles by means of successive redox and disproportionation reactions with the remaining AuIII species. Under nearly equimolar conditions, spherical nanoparticles are preferentially formed. At high AuIII concentrations, formation of anisotropic gold nanoparticles is observed. The chemistry of the ranelate ions is yet at very beginning, but exciting perspectives can already be seen in chemistry, medicine and in dyes industry.

Neste trabalho relata-se pela primeira vez a determinação de adenosina por um biossensor baseado em tirosinase. O biossensor foi desenvolvido mediante a modificação de um eletrodo de carbono impresso (SPE) com nanopartículas de ouro (AuNPs), tirosinase (Tyr) e Nafion, denominado biossensor Nafion/Tyr/AuNPs/SPE. As AuNPs sintetizadas possuem diâmetro médio de 15,0 ± 1,1 nm e sua função é melhorar a via de condução de elétrons entre a enzima e o eletrodo. Utilizou-se o aprisionamento com filme Nafion® para evitar a lixiviação enzimática da superfície do eletrodo. A tirosinase imobilizada apresentou boa atividade frente ao substrato catecol. Verificou-se que a adenosina atua como um inibidor do tipo não-competitivo. O biossensor é estável durante pelo menos 45 dias. Além disso, foi realizada a eletro-oxidação da adenosina para sua determinação. O biossensor apresenta sensibilidade superior em comparação com SPE, AuNPs/SPE e Nafion/AuNPs/SPE. As curvas de calibração revelaram duas faixas lineares para as concentrações de adenosina, de 1,0 × 10-5 mol L-1 até 5,0 × 10-5 mol L-1 e entre 6,0 × 10-5 mol L-1 e 1,2 × 10-4 mol L -1. O limite de detecção (3 × (desvio padrão + média dos brancos)/coeficiente angular da curva) foi de 7,0 × 10-7 mol L-1. / In this work we report for the first time the determination of adenosine by a biosensor based on tyrosinase. The biosensor was developed by modifying a screen-printed carbon electrode (SPE) with gold nanoparticles (AuNPs), tyrosinase (Tyr) and Nafion, denoted as Nafion/Tyr/AuNPs/SPE biosensor. The synthesized AuNPs have a mean diameter of 15.0 ± 1.1 nm and their function is to improve the electron conduction pathway between the enzyme and the electrode. The entrapment with Nafion® film was selected to prevent the enzyme lixiviation from the electrode surface. Immobilized tyrosinase showed good activity with the catechol substrate. It was found that adenosine acts as a non-competitive type inhibitor. The biosensor is stable for at least 45 days. In addition, the electro-oxidation of adenosine was performed for its determination. The biosensor has superior sensitivity compared to SPE, AuNPs/SPE and Nafion/AuNPs/SPE. Calibration curves revealed two linear ranges for adenosine concentrations of 1,010-5 mol L-1 up to 5,010-5 mol L-1 and from 6,010-5 mol L-1 to 1,210-4 mol L-1. The detection limit (3 × (standard deviation + mean of blanks)/slope of the curve) was 7,010-7 mol L-1.

The current project work aims to develop a simple and sensitive immunoassay for prostate specific antigen (PSA) by using changes of fluorescence of gold nanoparticles with varying coverage of proteins. In this work we attempted to investigate the changes in optical properties caused by coating the nanoparticles with antibody-antigen complex. We wanted to construct biosensor that utilizes these changes to monitor biological bindings without fluorescent marker.The underlying idea of the project has been to use label free immunoassay to monitor not only presence or absence of antigens in sample solution but also to quantify the antigen concentration, we have tried to develop a simple and time and labour saving method based on a non competitive heterogeneous but label free immunoassay.There are many instrumentation techniques for analysis of changes of optical properties of nanoparticles used in an immunoassay, like absorption spectroscopy, surface plasmon resonance spectroscopy, Raman spectroscopy, time resolved fluorescence and electrochemical techniques [1]. In present work we have investigated whether the adsorption of antibodies onto Au (gold) nanoparticles would change the optical properties of antibodies to an extent sufficient to differentiate them from the free antibodies. We have furthermore investigated whether the subsequent antigen binding to antibodies also induces changes of optical properties sufficient for quantitative analysis. We have chosen to monitor optical properties via measurement of fluorescence because of its sensitivity and selectivity.Our objective here has been not only to investigate spectral changes but also to develop a robust assay protocol, for example with respect to the antibody binding and nanoparticles separation techniques. Two critical steps of the experimental procedure developed here have been (i) the separation of excess prostate specific monoclonal antibodies (PSA10) from the solution containing nanoparticles with adsorbed PSA10 and free PSA10, and the stability of Au-PSA10 conjugates, and (ii) quantification of the binding of PSA to PSA10 covered nanoparticles.We have encountered problems with agglomeration of gold nanoparticles, both naked and with PSA10 conjugates. The naked nanoparticles were “sticky” and bound easily with other materials, for example with agarose beads from the separation columns. Fortunately the coated nanoparticles turned out to be much more inert. This allowed the separation and, simultaneously, acted as a test for antibody coverage. / Uppsatsnivå: D

Nanoparticles are increasingly incorporated into consumer products because of their unique, size-dependent properties. Although these properties are commercially appealing, data are lacking regarding the fate and reactivity of nanoparticles once incorporated into materials. This information gap prevents accurate assessment of hazards that these materials potentially present to consumers and the environment. To address this concern, new research is needed to investigate the reactivity and transformations of nanoparticles. This dissertation describes the use of an electron transparent characterization platform to observe nanoparticle transformations. Nanoparticles were tethered to the surface of an analysis platform, exposed to a variety of conditions, and evaluated for reactivity and response. The characterization of silver nanoparticles revealed the generation of new daughter nanoparticles on surfaces in ambient humid conditions. Our observations showed that the transport of material is highly dependent on relative humidity and that pH equilibria drives the deposition of new particles and degradation. We discovered, by applying these findings to macro-silver objects, that bulk silver generates new nanoparticles on surfaces. This illuminated the possibility of other, yet undiscovered, naturally occurring nanoparticles. In the second model system, 1.5 nm gold nanoparticles were tethered by a robust metal oxide bond from the terminal group of the stabilizing ligand. This strategy facilitated precise control over thiol ligand removal using a dilute ozone oxidation. Tracking particle oxidation over time allowed us to gain unprecedented control over core exposure, size maintenance, and surface tethering. This platform was also utilized as a proof-of-concept for direct observation of transformations in complex media. Ligand and core transformations were monitored in a variety of biologically relevant conditions using tethered nanoparticles. Morphological and chemical transformations were characterized and correlated to results from solution monitoring. The use of a platform based approach to evaluating the reactivity of nanoparticles in the environment holds promise for evaluations of nanoparticles and their transformation products. The demonstration of monitoring reactivity in systems equilibria, carefully controlled transformations, or complex media shows the versatility of this strategy. Only through the use of this analysis platform was the direct observation of nanoparticle transformations possible. This dissertation includes previously published, unpublished, and co-authored materials. / 10000-01-01

O ouro foi considerado um metal pouco interessante do ponto de vista catalítico por muito tempo, devido ao fato de não quimiossorver moléculas como hidrogênio e oxigênio. Entretanto, suas propriedades catalíticas são reveladas quando suas dimensões são reduzidas a poucos nanômetros, particularmente menores do que 10 nm. Assim, nanocatalisadores de ouro vêm recebendo atenção devido as suas excelentes propriedades catalíticas e alta seletividade em reações de oxidação e redução. O presente trabalho descreve a síntese e caracterização de nanopartículas de ouro suportadas e sua aplicação em reações de oxidação de alcoóis para produção de aldeídos, cetonas e ésteres. Para facilitar a separação do catalisador, um suporte magnético composto de magnetita revestida com sílica foi desenvolvido. A síntese das nanopartículas de ouro suportadas foi realizada de duas maneiras: (I) pela impregnação do suporte com espécies aniônicas de ouro seguido de redução e (II) pela impregnação de nanopartículas de ouro pré-sintetizadas. Em todos os casos nanopartículas de ouro na faixa de 5 nm foram obtidas. A etapa de redução do metal impregnado no suporte foi investigada em detalhe através de duas estratégias: a redução térmica e a redução por hidrogênio. Os testes catalíticos para as reações de oxidação de alcoóis mostraram que os catalisadores sintetizados apresentam altas taxas de conversão e seletividade, porém dependentes do método de preparação utilizado / Gold in the bulk form has been regarded to be an uninteresting metal from the point of view of catalysis, as it is chemically inert towards chemisorption of reactive molecules such as oxygen and hydrogen. However, the catalytic properties of gold are revealed when the size is reduced to few nanometers, particularly with dimension less than 10 nm. Therefore, gold nanocatalysts have received great attention due to the excellent catalytic properties and high selectivity in oxidation and reduction reactions. This master thesis describes the synthesis and characterization of supported gold nanoparticles and their application in alcohol oxidation reaction to produce aldehydes, ketones and esters. In order to improve the catalyst separation and recovery, a magnetic support comprised of magnetite coated by silica was developed. The supported gold nanoparticles were synthesized in two different ways: (I) by impregnation of anionic gold species on silica surface followed by metal reduction, and (II) by impregnation of pre-synthesized gold nanoparticles on the support. In all examples supported gold nanoparticles of about 5 nm were obtained. The reduction step (of the metal impreganted on the support) was investigated in detail by two different strategies: thermal reduction and reduction by hydrogen. The synthesized catalysts showed high conversion rates and selectivity in the catalytic reactions of alcohol oxidation, but those are dependent on the preparation method