No description available.

A low cost compact diagnostic has many implications in today’s society. Smart phone technology has exponentially grown and with it the imaging capabilities associated with smart phones. The goals of this research are i) to determine the feasibility of combining in the field smart phone images with color dependent assay results, ii) to develop a MatLab® image analysis code to analyze these results, and iii) compare limits of detection between the un-aided eye and MatLab® image analysis software. Orange G dye is used to create a stock solution and subsequent titers for analysis. Autocad is used to design an assay platform of 10x10 wells that are printed via a Xerox® Phaser printer with wax ink onto nitrocellulose paper. Dilutions are performed and pipetted into the wells. The image analysis code is used to determine hue, saturation, and value (HSV) values of wells. A limit of detection study using the dye is performed. HSV values are used to form calibration curves. The resulting curve fit equations are then integrated into the image analysis code to determine dye concentration. Finally, the complete capability is demonstrated by using an analogous 10x10 well experimental nitrocellulose sheet, which included a follow-up experiment via a spot check analysis. This study illustrates the feasibility of a low cost image analysis as a tool for lateral flow assay diagnostic versus the unaided eye. Future work includes using this protocol in conjunction with a lateral flow immunoassay and developing an application for the analysis.

Cancer is one of the leading causes of death worldwide, and affects roughly 1.5 million new people in the United States every year. One of the leading tools in the detection and treatment of cancer is radiation. Tumors can be detected and identified using CT or PET scans, and can then be treated with external beam radiotherapy or brachytherapy. By taking advantage of the physical properties of gold and the biological properties of nanoparticles, gold nanoparticles (GNPs) can be used to improve both cancer radiotherapy and imaging. By infusing a tumor with GNPs, either using passive extravasation of nanoparticles by the tumor vasculature or active targeting of an antibody-conjugated nanoparticle to a specific tumor marker, the higher photon cross-section of gold will cause more radiation dose to be deposited in the tumor during photon-based radiotherapy. In principle, this would allow escalation of dose to the tumor while not increasing the dose to normal healthy tissue. Additionally, if a tumor infused with GNPs was irradiated by an external kilo-voltage source, the fluorescence emitted by the gold atoms would allow one to localize and quantify the GNP concentration. This work has two main aims: to quantify the GNP-mediated dose enhancement during GNRT on a nanometer scale, and to develop a refined imaging modality capable of quantifying GNP location and concentration within a small-animal-sized object. In order to quantify the GNP-mediated dose enhancement on a nanometer scale, a computational model was developed. This model combines both large-scale and small-scale calculations in order to accurately determine the heterogeneous dose distribution of GNPs. The secondary electron spectra were calculated using condensed history Monte Carlo, which is able to accurately take into account changes in beam quality throughout the tumor and calculate the average energy spectrum of the secondary charged particles created. Then, the dose distributions of these electron spectra were calculated on a nanometer scale using event-by-event Monte Carlo. The second aim is to develop an imaging system capable of reconstructing a tomographic image of GNP location and concentration in a small animal-sized object by capturing gold fluorescence photons emitted during irradiation of the object by an external beam. This would not only allow for localization of GNPs during gold nanoparticle-aided radiation therapy (GNRT), but also facilitate the use of GNPs as imaging agents for drug-delivery or other similar studies. The purpose of this study is to develop a cone-beam implementation of XFCT that meets realistic constrains on image resolution, detection limit, scan time, and dose. A Monte Carlo model of this imaging geometry was developed and used to test the methods of data acquisition and image reconstruction. The results of this study were then used to drive the production of a functioning benchtop, polychromatic cone-beam XFCT system.

The path towards mitigation of anthropogenic greenhouse gas emissions lies in the transition from conventional to sustainable energy resources. The Hydrogen Economy, a cyclic economy based on hydrogen as a fuel, is suggested as a tool in the necessary energy transition. Photocatalysis makes use of sunlight to promote thermodynamically non-favoured reactions such as water splitting, allowing for sustainable hydrogen production. Harvesting thermal energy along with photonic energy is an interesting concept to decrease the activation energy of water splitting (i.e. ΔG = + 237.2 kJ∙mol−1). This work aims to confront this hypothesis in a gas phase photo-thermal reactor designed specifically for this study. The photocatalyst chosen is graphitic carbon nitride (g-C3N4), an organic semiconductor possessing a narrow band gap (i.e. 2.7 eV) as well as a band structure which theoretically permits water splitting. The photocatalytic performance of Pt/g-C3N4 for hydrogen evolution was tuned by altering its synthetic temperature. Electron paramagnetic resonance was used to gain insight on the evolution of the photocatalyst activity with synthesis temperature. Then, gold nanoparticles were deposited on g-C3N4 surface. Localized surface plasmon resonance properties of gold nanoparticles are reported in the literature to be influenced by temperature. Therefore Au/g-C3N4 appeared as a promising candidate for photo-thermal water splitting. X-ray spectroscopy unveiled interesting observations on the gold oxidation state. Moreover, under specific reduction conditions, gold nanoparticles with a wide variety of shapes characterized by sharp edges were formed. Finally, the development of the photo-thermal reactor is presented. The design process and the implementation of this innovative reactor are discussed. The reactor was successfully utilized to probe photoreactions. Then, the highly energy-demanding photocatalytic water splitting was proven not to be activated by temperature in the photo-thermal apparatus.

The increasing demands for biopharmaceuticals to treat different diseases have raised concerns about controlling the quality and efficacy of such pharmaceuticals. The design and formulation of a stable protein or peptide based biopharmaceutical runs into the limitation that at high concentrations (> 100 mg/ml) or during long storage process the drug undergoes aggregation. During synthesis, purification, storage or packaging of these drugs different kinds of stresses like chemical, oxidative, thermal, shear, etc. are encountered. These stresses promote the non-native aggregation of protein and peptide based drugs. Injection or administration of such drugs if contaminated with aggregates causes patient discomfort or development of an antibody which can adversely affect patient’s conditions. This brings out the necessity of finding a way so that such aggregation is avoided. Nanoparticles have been used as vehicles for drug delivery and diagnostic agents in biology for a while. The surface of the nanoparticles is known to adsorb small as well as large molecules with different kinetics and energetics of interaction. I have used nanoparticles to adsorb proteins to protect them against aggregation when they are subjected to denaturing conditions. The effectiveness of the nanoparticles in stopping protein aggregation, recovery of the proteins and reversibility of the adsorption process, the catalytic activity of the proteins before and after adsorption on the surface have all been studied in details. The work described here has been divided in 8 chapters and the contents of each chapter are described below. In Chapter 1 I have provided a brief introduction to the protein aggregation problem. The motivation and scope of the current work has been presented in this chapter. Materials and methods have been described in Chapter 2. Synthesis of gold and silica nanoparticles, their characterization and stability under experimental conditions have been illustrated in this chapter. The spectroscopic assays and techniques which I have used to study the effect of gold and silica nanoparticles on protein aggregation have been discussed at lengths in this chapter. In Chapter 3 I have demonstrated the effect of gold nanoparticles on thermal aggregation of alcohol dehydrogenase (ADH). The size of the nanoparticle was varied in the range of 15-60 nm and the effect was measured by various spectroscopic assays and techniques. I have observed that gold nanoparticles prevent thermal aggregation of ADH and the efficiency is high. Gold nanoparticles in nanomolar or even picomolar concentrations are capable of preventing the aggregation of ADH at micromolar concentrations. In Chapter 4 the role of gold nanoparticles as suppressor of protein aggregation was extended to another protein, insulin. Chemically induced aggregation of insulin using dithiothreitol (DTT) in the presence of gold nanoparticles was studied in the same manner as was done for ADH. Similar prevention property of gold nanoparticles was established by making the observation independent of the method of denaturation or the type of protein used in the prevention experiments. In Chapter 5 huge second harmonic light scattering (SHS) signal from pure gold nanoparticles has been used to measure the free energy of interaction of ADH and insulin with nanoparticles in solution, for the first time. The change in the second harmonic scattered signal was monitored which decreased steadily as a function of added protein concentration to the aqueous solution of gold nanoparticles. The fitting of the second harmonic signal decay was done with a modified Langmuir adsorption isotherm to extract the free energy change in the interaction and the number of protein molecules adsorbed on the surface. In Chapter 6 I have demonstrated a way to recover the adsorbed ADH and insulin from the gold nanoparticle surface and tested the activity of ADH by an assay. The structure of the proteins in the adsorbed state has been probed by CD spectroscopy and described in this chapter. It is found that ADH retains its activity in the adsorbed state. Both the proteins retain the native secondary structures in their adsorbed state. However, the structures change drastically under denaturing conditions. In Chapter 7 the effect silica nanoparticles which are known to have hydrophilic surface has been examined on the aggregation of ADH and insulin in pretty much the same way as was done with gold nanoparticles. The efficiency of silica nanoparticle was found to be lower compared to gold nanoparticles. In addition, the size dependency of prevention efficiency of silica and gold nanoparticles was found to be completely opposite to each other. In Chapter 8 I have presented the overall summary and possible future directions of this work

CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas Gerais / Na presente tese foram desenvolvidas três plataformas para a construção de biossensores visando o diagnóstico molecular da hepatite C, hepatite B e artrite reumatoide, por técnicas eletroquímicas, ópticas e microscópicas, usando amostras reais. Os genossensores para hepatites C e B foram desenvolvidos sobre a superfície de um eletrodo de ouro modificado com nanomateriais, sendo esses o óxido de grafeno e o óxido de grafeno reduzido, respectivamente. Em todos os biossensores propostos a interação da sonda com o alvo foi efetivamente verificada pelas diferentes técnicas. No caso do genossensor para hepatite C, o óxido de grafeno foi modificado quimicamente com etilenodiamina e apresentou limites de detecção e quantificação de 1:483 (v/v) e 1:145 (v/v), respectivamente, usando amostras de soro de pacientes positivos. A interação da sonda específica do HCV: gRNA causou uma redução na amplitude de resposta de corrente de cerca de 2,9 vezes quando comparada ao controle negativo, usando a VPD. O genossensor para a hepatite B a sonda foi imobilizada sobre eletrodo de ouro contendo óxido de grafeno reduzido, ouro descoberto e nanoparticulas de ouro. A análise usando VPD indica que a adição de DNA genômico de HBV provocou um aumento de cerca de 1,4 vezes na amplitude de corrente de pico quando comparado ao controle negativo. Em adição, análises de SPR mostraram que as amostras positivas de HBV resultaram em uma alteração de cerca de 15 vezes em comparação com as amostras negativas. No biossensor desenvolvido para o diagnóstico da artrite reumatoide foi utilizado um eletrodo de grafite modificado com um filme poli(3-hidroxibenzóico), no qual foi imobilizado um peptídeo mimético que reconhece o anticorpo anti-CAIII. O sensor mimético desenvolvido permitiu a distinção entre amostras positivas e negativas para a artrite reumatóide, uma vez que apresentou uma diminuição expressiva no sinal de corrente de cerca de 2,2 vezes, quando comparado ao soro negativo. Assim, foi possível desenvolver plataformas analíticas, seletivas e específicas fornecendo novas abordagens para o diagnóstico clínico e aplicações point-of-care para o monitoramento de doenças inflamatórias e infecciosas. / In the present thesis, three biosensing platforms aiming the molecular diagnosis of hepatitis C, hepatitis B and rheumatoid arthritis were developed by electrochemical, optical and microscopic techniques using real samples. The genosensors for the diagnosis of hepatitis C and B were developed on a gold electrode modified with nanomaterials, being these graphene oxide and reduced graphene oxide, respectively. In all proposed biosensors the interaction of the probe with the target was effectively verified by the different techniques. In the case of the genossensor for hepatitis C, graphene oxide was chemically modified with ethylenediamine and showed limits of detection and quantification of 1:483 (v/v) and 1:145 (v/v), respectively, using serum samples from positive patients. The interaction of the HCV probe and the gRNA caused a reduction in current response amplitude of about 2.9 fold as compared to the negative control, using the DPV. The genossensor for hepatitis B probe was immobilized on a gold electrode containing reduced graphene oxide, gold disks and gold nanoparticles. Analysis using DPV indicates that the addition of HBV gDNA caused an increase of about 1.4 times in peak current amplitude, when compared to the negative control. In addition, SPR analyzes showed that positive samples of HBV resulted in a change of about 15- fold compared to negative samples. In the biosensor developed for the diagnosis of rheumatoid arthritis, a graphite electrode modified with a poly (3-hydroxybenzoic) film was used, in which a mimetic peptide that recognizes the anti-CAIII antibody was immobilized. The developed mimetic sensor allowed the distinction between positive and negative samples for rheumatoid arthritis, since it presented an decrease in the current signal of about 2.2 times, when compared to the negative serum. Thus, it was possible to develop analytical, selective and specific platforms, providing new approaches for clinical diagnosis and point-of-care applications, for the monitoring of inflammatory and infectious diseases. / Tese (Doutorado)

The emergence of novel electronic, optical and magnetic properties in ordered two-dimensional (2D) nanoparticle ensembles, due to collective dipolar interactions of surface plasmons or excitons or magnetic moments have motivated intense research efforts into fabricating functional nanostructure assemblies. Such functional assemblies (i.e., highly-integrated and addressable) have great potential in terms of device performance and cost benefits. Presently, there is a paradigm shift from lithography based top-down approaches to bottom-up approaches that use self-assembly to engineer addressable architectures from nanoscale building blocks. The objective of this dissertation was to develop appropriate processing tools that can overcome the common challenges faced in fabricating floating gate memory devices using self-assembled 2D metal nanoparticle arrays as charge storage nodes. The salient challenges being to synthesize monodisperse nanoparticles, develop large scale guided self-assembly processes and to integrate with Complementary Metal Oxide Semiconductor (CMOS) memory device fabrication processes, thereby, meeting the targets of International Technology Roadmap for Semiconductors (ITRS) – 2017, for non-volatile memory devices. In the first part of the thesis, a simple and robust process for the formation of wafer-scale, ordered arrays using dodecanethiol capped gold nanoparticles is reported. Next, the results of ellipsometric measurements to analyze the effect of excess ligand on the self-assembly of dodecanethiol coated gold nanoparticles at the air-water interface are discussed. In a similar vein, the technique of drop-casting colloidal solution is extended for tuning the interparticle spacing in the sub-20 nm regime, by altering the ligand length, through thiol-functionalized polystyrene molecules of different molecular weights. The results of characterization, using the complementary techniques of Atomic Force Microscopy (AFM) and Field-Emission Scanning Electron Microscopy (FESEM), of nanoparticle arrays formed by polystyrene thiol (average molecular weight 20,000 g/mol) grafted gold nanoparticles (7 nm diameter) on three different substrates and also using different solvents is then reported. The substrate interactions were found to affect the interparticle spacing in arrays, changing from 20 nm on silicon to 10 nm on a water surface; whereas, the height of the resultant thin film was found to be independent of substrate used and to correlate only with the hydrodynamic diameter of the polymer grafted nanoparticle in solution. Also, the mechanical properties of the nanoparticle thin films were found to be significantly altered by such compression of the polymer ligands. Based on the experimental data, the interparticle spacing and packing structure in these 2D arrays, were found to be controlled by the substrate, through modulation of the disjoining pressure in the evaporating thin film (van der Waals interaction); and by the solvent used for drop casting, through modulation of the hydrodynamic diameter. This is the first report on the ability to vary interparticle spacing of metal nanoparticle arrays by tuning substrate interactions alone, while maintaining the same ligand structure. A process to fabricate arrays with square packing based on convective shearing at a liquid surface induced by miscibility of colloidal solution with the substrate is proposed. This obviates the need for complex ligands with spatially directed molecular binding properties. Fabrication of 3D aggregates of polymer-nanoparticle composite by manipulating solvent-ligand interactions is also presented. In flash memory devices, charges are stored in a floating gate separated by a tunneling oxide layer from the channel, and the tunneling oxide thickness is scaled down to minimize power consumption. However, reduction in tunneling oxide thickness has reached a stage where data loss can occur due to random defects in the oxide. Using metal nanoparticles as charge-trapping nodes will minimize the data loss and enhance reliability by compartmentalizing the charge storage. In the second part of the thesis, a scalable and CMOS compatible process for fabricating next-generation, non-volatile, flash memory devices using the self-assembled 2D arrays of gold nanoparticles as charge storage nodes were developed. The salient features of the fabricated devices include: (a) reproducible threshold voltage shifts measured from devices spread over cm2 area, (b) excellent retention (>10 years) and endurance characteristics (>10000 Program/Erase cycles). The removal of ligands coating the metal nanoparticles using mild RF plasma etching was found, based on FESEM characterization as well as electrical measurements, to be critical in maintaining both the ordering of the nanoparticles and charge storage capacity. Results of Electrostatic Force Microscope (EFM) measurements are presented, corroborating the need for ligand removal in obtaining reproducible memory characteristics and reducing vertical charge leakage. The effect of interparticle spacing on the memory characteristics of the devices was also studied. Interestingly, the arrays with interparticle spacing of the order of nanoparticle diameter (7 nm) gave rise to the largest memory window, in comparison with arrays with smaller (2 nm) or larger interparticle spacing (20 nm). The effect of interparticle spacing and ligand removal on memory characteristics was found to be independent of different top-oxide deposition processes employed in device fabrication, namely, Radio-frequency magnetron sputtering (RF sputtering), Atomic Layer Deposition (ALD) and electron-beam evaporation. In the final part of the thesis, a facile method for transforming polydisperse citrate capped gold nanoparticles into monodisperse gold nanoparticles through the addition of excess polyethylene glycol (PEG) molecules is presented. A systematic study was conducted in order to understand the role of excess ligand (PEG) in enabling size focusing. The size focusing behavior due to PEG coating of nanoparticles was found to be different for different metals. Unlike the digestive ripening process, the presence of PEG was found to be critical, while the thiol functionalization was not needed. Remarkably, the amount of adsorbed carboxylate-PEG mixture was found to play a key role in this process. The stability of the ordered nanoparticle films under vacuum was also reported. The experimental results of particle ripening draw an analogy with the well-established Pechini process for synthesizing metal oxide nanostructures. The ability to directly self-assemble nanoparticles from the aqueous phase in conjunction with the ability to transfer these arrays to any desired substrate using microcontact printing can foster the development of applications ranging from flexible electronics to sensors. Also, this approach in conjunction with roll-to-roll processing approaches such as doctor-blade casting or convective assembly can aid in realizing the goal of large scale nanostructure fabrication without the utilization of organic solvents.

La photothérapie dynamique (PTD) est un traitement alternatif du cancer qui nécessite l’utilisation de chromophores (photosensibilisateurs) capables d’induire la mort cellulaire suite à une irradiation lumineuse. Les nanoparticles d’or (AuNP), grâce à leur phénomène de résonance plasmon localisée, peuvent exalter les propriétés photophysiques des chromophores localisés à leur surface. L’utilisation d’une excitation biphotonique, dans le proche infrarouge, peut être utilisée pour améliorer l’action thérapeutique (PTD) ou diagnostique (imagerie de fluorescence) des chromophores en augmentant la profondeur de pénétration dans les tissus et la résolution tridimensionnelle de la microscopie biphotonique.Lors de ce travail, l’élaboration de nouvelles nanoparticules hybrides est proposée, présentant des applications potentielles en bioimagerie (sondes brillantes) et comme photosensibilisateurs pour la PTD. Ces nanoparticules sont composées d’un cœur d’or sur lequel sont greffés des conjugués polymère-chromophores biphotoniques. La stratégie de synthèse a consisté à : i) synthétiser des conjugués polymère-chromophores biphotoniques solubles dans l’eau ; ii) les greffer de manière orientée à la surface des AuNP. La synthèse des conjugués polymère-chromophores hydrosolubles on été synthétisés via le couplage efficace de chromophores hydrophobes en position latérale des copolymères P(NAM-co-NAS) bien-définis, obtenus par la techniques de polymérisation radicalaire contrôlée RAFT. Cette stratégie permet le contrôle à la fois de la longueur des chaînes polymère formées (2 000 g.mol-1 < Mn plus < 37 000 g.mol-1) et du nombre de chromophores couplés par chaîne (de 1 à 21). Le greffage orienté de ces conjugués à la surface des AuNP a été mis en évidence (TEM, ATG) et les densités de greffage se sont avérées élevées (~0.5chaîne/nm²). Un des rôles de la chaîne polymère étant de contrôler la distance entre les chromophores et la surface des AuNP. Il a été mis en évidence que l’augmentation de la longueur de chaine des conjugués induisait, outre une augmentation de la couronne greffée (par MET) sur les AuNP, une augmentation de l’émission de fluorescence de ces conjugués polymère-chromophores. Enfin, les propriétés biologiques des conjugués avant et après greffage sur les AuNP ont été évaluées in cellulo, mettant en valeur leur potentiel pour des applications thérapeutiques et diagnostiques. / Photodynamic therapy (PDT) is an alternative treatment of cancer requiring the use of chromophore molecules (photosensitizers), which can induce cell death after light excitation. Gold nanoparticles (AuNP), exhibiting localized Surface Plasmon Resonance, can enhance the photophysical response of chromophores located in their vicinity, and thus improve their therapeutic action. Moreover, the use of highly localized two-photon chromophores (photosensitizers and fluorophores), capable to undergo a localized excitation by light in the Near InfraRed region, should increase the penetration depth into tissues, thus improve the treatment efficiency (by PDT) and the imaging (by fluorescence microscopy) of cancer tissues.In this work, we describe the elaboration of water-soluble hybrid nano-objects for PDT and fluorescence bioimaging applications, composed of two-photon chromophore-polymer conjugates grafted onto gold nanoparticles. In order to obtain these nano-objects we follow a multistep strategy: i) the synthesis of a well-defined water-soluble chromophore-polymer conjugates; ii) the end-group oriented grafting of chromophore-polymer conjugates onto 20 nm AuNP. The coupling of hydrophobic two-photon chromophores on linear water-soluble copolymer chains (poly(N-acryloylmorpholine-co-N-acryloxysuccinimide)), obtained by controlled/living RAFT polymerization, resulted in well-defined water-soluble chromophore-polymer conjugates, with different polymer lengths (2 000 g.mol-1 < Mn < 37 000 g.mol-1) and architectures (random or block), and a controlled number of chromophores per chain (varying between 1 and 21). Their grafting onto 20 nm AuNP gave water-soluble hybrid nano-objects with high grafting densities (~0.5 chains/nm²). The role of the polymer chain being to tune the distance between chromophores and AuNP surface, we have evidenced the increase in the polymer corona thickness of grafted AuNP (estimated by TEM) with the increasing polymer Mn, corroborating with the corresponding distance-dependent fluorescence properties of those. Finally, the in cellulo biological properties of two-photon chromophore-polymer conjugates, before and after grafting onto AuNP, have been investigated, highlighting their potential for two-photon bioimaging and PDT applications.

[pt] O controle de parâmetros físicos e químicos das nanopartículas, tais quais, forma, composição e tamanho, além da interação entre metal e suporte, são fatores determinantes no desenvolvimento de um nanocatalisador com uma boa performance. Desse modo, nanopartículas de ouro foram incorporadas em nanofios de céria e utilizados como nanocatalisador para a oxidação seletiva do tioanisol. Sendo a sua morfologia 1D, com grande área superficial específica, diâmetros finos, alta concentração de vacância de oxigênio e pequenas NPs de Au uniformemente distribuídas na superfície do CeO2, além de espécies oxidadas de ouro, temos em nosso material características que o torna favorável a reação de oxidação. Os nanofios de CeO2-Au demonstraram uma melhora na performance da oxidação seletiva do tioanisol quando comparados aos nanofios de céria puros, e ao material comercial com e sem a deposição de NPs de Au. Os nanofios de céria obtiveram uma seletividade de 100 porcento para o metil fenil sulfóxido, e uma conversão de 53 porcento em 2 h de reação. O impacto da temperatura também foi observado, demonstrando que esse é, também, um fator importante na análise da atividade de um catalisador. / [en] The control over physical and chemical parameters of nanoparticles, such as shape, composition and size as well as the interactions between metal and support, are important factors in the development of a nanocatalyst with high activity. In this context, gold nanoparticles were incorporated the surface of ceria nanowire for application as nanocatalysts towards the selective oxidation of thioanisole. Considerin their one-dimensional morphology, high specific surface area, thin diameters, significant concentration of oxygen vacancies, and small Au NPs uniformly deposited at the CeO2 nanowires surface, our material displayed characteristics that makes them favorable for oxidations reactions. The CeO2-Au nanowires showed improved catalytic performances in the selective oxidation of thioanisol relative to pure CeO2 nanowires and commercial CeO2 with and without Au NPs deposited. CeO2-Au nanowires catalyzed the desired product with 100 percent of selectivity and 53 percent of conversion. The impact of temperature, such as the solvent, were also observed revealing that these factors also influences in the activity of these nanocatalyst.

Goldnanopartikel werden in der kolloidalen Katalyse als Modellsystem genutzt, um den Einfluss des Partikelgröße, der Partikelform und der Zusammensetzung in bimetallischen Systemen sowie der Ligandensphäre auf die katalytische Reduktion von 4-Nitrophenol zu 4-Aminophenol zu untersuchen. Goldnanopartikel eignen sich vor allem deshalb als Modellsystem, da sie in kurzer Zeit, in hohen Ausbeuten und mit definierten Eigenschaften hergestellt werden können. Es konnte erstmals nachgewiesen werden, dass Goldnanopartikel mit einem Durchmesser von 13 nm die höchste katalytische Umsetzungsrate bei der Reduktion von 4-Nitrophenolzu 4-Aminophenol besitzen. Im Zuge dieser Arbeit wird dieses Aktivitätsmaximum der Nanopartikel näher untersucht. Dazu werden drei Aspekte vorgestellt: die Abhängigkeit von der Goldnanopartikelform, die Abhängigkeit der Substratgröße und der Einfluss der Ligandensphäre auf die Katalyse. Überraschenderweise ist CTAB als oberflächenaktiver Ligand ein Co-Katalysator bei der Reduktion, während die Anwesenheit von Natriumcitrat die Reaktion verlangsamt. Es wurden Aspekte wie die Konzentration und die Größe der Goldnanopartikel in dem komplexen Wechselspiel der Aktivitäten des Katalysators und Co-Katalysators untersucht. Dies führte zu der beispielgebenden Erkenntnis, dass oberflächenaktive Liganden mit positiver Ladung und Stickstofffunktionen die Katalyse positiv beeinflussen. In einer weiteren Studie wurde der Reaktionsmechanismus der 6-Elektronenreduktion von 4-Nitrophenol zu 4-Aminophenol erforscht. Es konnte zum ersten Mal gezeigt werden, dass die Reduktion in zwei Teilschritten abläuft. N-Arylhydroxylamin ist als wichtiges Intermediat in der Lösung der Reduktion erstmals nachgewiesen worden. Drei kinetische Regime werden für die Reduktion von 4-Nitrophenol gefunden und geben einen Einblick in die Oberflächenreaktion von Nitroaromaten an Goldnanopartikeln. / Gold nanoparticles as model systems in colloidal catalysis are used to gain insights into the decisive parameters of the catalytic model reduction. Size, shape, composition of bimetallic systems, and ligand sphere are factors influencing the reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride in the presence of gold nanoparticles. The increasing interest in gold nanoparticle catalysis is mainly due to their stability, their fast and high yield synthesis as well as their extraordinary diversity of the modes of preparation. This thesis is assigned to unravel the important parameters of gold nanoparticle catalysis. In the first part of the thesis, CTAB-stabilized gold nanoparticles were synthesized by applying the seeding-growth approach in order to gain information about the size dependence of the catalytic reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride. Unexpectedly, CTAB-stabilized gold nanoparticles with a diameter of 13nm were most efficient in this complex system. In this context, molecular aspects such as shape, size of the substrate and ligand sphere were discussed as possible reasons for the enhanced activity for medium sized gold nanoparticles. Here, it was shown for the first time that the ligand sphere plays a crucial role in colloidal catalysis. Micellar catalysis with colloidal gold nanoparticles was performed by means of ligand exchange procedures. In addition, this thesis shows for the first time that intermediates can be unambiguously identified in the reaction solution with colloidal gold nanoparticles as catalysts. 4-N-hydroxylaminophenol was found to be the key intermediate in this system. In this context, three kinetic regimes which were crucial for the aromatic nitro reduction are found to cover the reaction kinetics. Thus, this thesis provides new insight into the catalytic process itself and leads to a better understanding of the catalytic activity of gold nanoparticles.