IV Resumo Título: Nanoestruturas de Dissulfeto de Molibdênio: Síntese e caracterização para produção de Hidrogênio Mestrando: André Luís Silveira Fraga Orientador: Prof. Marcos José Leite Santos Palavras Chave: nanoestruturas de MoS2, nanopartículas de ouro, semicondutores, produção de hidrogênio. Neste trabalho é apresentada a síntese e caracterização de nanoestruturas de MoS2 e nanoestruturas de MoS2 decoradas com nanopartículas de ouro. O MoS2 foi obtido através de rota hidrotermal a 200 °C durante períodos de síntese de 2, 6, 12 e 24 horas. Como precursores foram utilizados molibdato de sódio, ácido 3-mercaptopropiônico, cisteamina e L-cisteína. Para avaliar o efeito da presença dos ligantes nas estruturas, as amostras de MoS2 foram tratadas térmicamente a temperaturas de 250, 550 e 750 °C, em atmosfera de argônio. Com o objetivo de avaliar o efeito da presença de nanopartículas de ouro nas propriedades fotocatalíticas do material, foi realizada a síntese in situ de nanopartículas de ouro aderidas às estruturas de MoS2. Os materiais foram caracterizados através das técnicas de difração de raios X (DRX), microscopia eletrônica de transmissão (MET), microscopia eletrônica de varredura (MEV) e espectroscopia do ultravioleta e visível (UV-Vis). As áreas superficiais e quantidade de poros foram avaliadas através das técnicas de BET (Brunauer, Emmett and Teller) e DFT (density functional theory). O precursor ácido 3-mercaptopropiônico resultou na formação de aglomerados de nanofolhas com cerca de 500 nm de diâmetro na sua maior dimensão. Ao usar cisteamina e L-cisteína foram obtidas nanoestruturas com formato de nanoflores com cerca de 300 nm de diâmetro formadas por pétalas com cerca de 30 nm. Um resultado interessante foi a rápida formação das nanoflores na presença de L-cisteína. As estruturas de nanoflores apresentaram produção de hidrogênio de até 9,6 mmol/gh. / In this work the synthesis and characterization of MoS2 nanostructures and MoS2 nanostructures decorated with gold nanoparticles is presented. The materials were obtained by hydrothermal route at 200 °C during synthesis periods of 2, 6, 12 and 24 hours. Sodium molybdate was used as Molybdenium precursor and 3-mercaptopropionic acid, cysteamine and L-cysteine as sulfur precursors. To evaluate the effect of ligands on the structures, the MoS2 samples were thermally treated at 250, 550 and 750 °C under argon atmosphere. The effect of gold nanoparticles on the photocatalytic properties of the material was evaluated by obtaining and materials with gold nanoparticle adhered to the MoS2 structures. The materials were characterized by X-ray diffraction (XRD) techniques, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and ultraviolet and visible spectroscopy (UV-Vis). The surface areas and amount of pores were evaluated using BET (Brunauer, Emmett and Teller) and DFT (density functional theory) techniques. The precursor 3-mercaptopropionic acid resulted in the formation of nano-foil agglomerates of about 500 nm in diameter. On the other hand, when using cysteamine and L-cysteine, flower-shaped nanostructures of about 300 nm in diameter formed by petals of about 30 nm were obtained. An interesting result was the rapid formation of nanoflores in the presence of L-cysteine. Nanoflower structures showed hydrogen production up to 9.6 mmol / gh.

O objetivo deste estudo foi sintetizar nanopartículas de ouro (AuNPs) em meio aquoso, transferí-las para diferentes meios orgânicos, e avaliar sua estabilidade (não-agregação) nesses meios, com o intuito de otimizar a exploração de suas propriedades ópticas. Foi utilizado o ácido tetracloroáurico (HAuCl4) como precursor de ouro metálico em meio aquoso e fez-se a transferência para clorofórmio (CHCl3) e diclorometano (CH2Cl2). Como agente de transferência, utilizou-se o polietilenoglicol tiolado (PEGSH) junto com o dodecanotiol (DDT). O PEG-SH foi adicionado na fase aquosa para evitar a agregação das AuNPs, assim como em fase orgânica, o DDT foi adicionado como agente estabilizador, pois sua cadeia alifática promove interações hidrofóbicas entre as partículas. Avaliou-se dois diâmetros médios de nanopartículas. A eficiência de transferência e a distribuição de tamanho das AuNPs foram estudadas utilizando a espectroscopia UV-Vis, espalhamento dinâmica de luz e microscopia eletrônica de transmissão. As nanopartículas denominadas AuNPs1 apresentaram AbsRPLS média de 0,8314 em ʎmédio = 521 nm e as AuNPs2 AbsRPLS média de 1,2643 em ʎmédio = 526 nm. Quando as AuNPs foram transferidas para solventes orgânicos, os espectros de absorção obtidos por UV-Vis apresentaram deslocamento da banda RPLS para o vermelho, em CHCl3, ʎAuNPs1 = 531 nm e ʎAuNPs2 = 534 nm; em CH2Cl2, ambas as soluções apresentaram ʎ = 530 nm. Este deslocamento é um dos fatores que indicaram a não-agregação das AuNPs. Em DLS, foi confirmada a nãoagregação. Em CHCl3, as AuNPs1 apresentaram eficiência de transferência de 97,27% e as AuNPs 98,88%, enquanto, em diclorometano, apenas 80,21% das AuNPs foram transferidas. As AuNPs apresentaram ao longo do tempo maior estabilidade em CHCl3 do que em CH2Cl2. Após a transferência para o CHCl3, as AuNPs foram separadas deste solvente e redissolvidas em outros solventes orgânicos com diferentes índices de refração: álcool benzílico, etanol e dimetilsulfóxido (DMSO). As AuNPS permaneceram visivelmente estáveis somente em álcool benzílico, pois nos outros solventes foi observado que a solução coloidal apresentou perda da coloração e por UV-Vis foi verificada a diminuição da banda da RPLS em DMSO e a ausência em etanol. / The objective of this study was to synthesize gold nanoparticles (AuNPs) in aqueous media, transfer them to different organic media, and evaluate their stability (non-aggregation) in these media, in order to optimize the exploration of their optical properties. Tetrachlorouric acid was used as the gold precursor in aqueous medium and transferred to chloroform (CHCl3) and dichloromethane (CH2Cl2). As the transfer agent, thiolated polyethylene glycol (PEG-SH) was used along with dodecanethiol (DDT). PEG-SH was added in the aqueous phase to prevent AuNPs from aggregating, as well as in the organic phase, DDT was added as a stabilizing agent because its aliphatic chain promotes hydrophobic interactions between the particles. Two average nanoparticle diameters were evaluated. The transfer efficiency and size distribution of the AuNPs were studied using UV-Vis spectroscopy, dynamic light scattering and transmission electron microscopy. The nanoparticles named AuNPs1 presented mean AbsRPLS of 0,8314 in ʎmedium = 521 nm and the AuNPs2 AbsLSPR mean of 1,2643 in ʎmedium = 526 nm. When the AuNPs were transferred to organic solvents, the absorption spectra obtained by UV-Vis showed red band shift in CHCl3, ʎAuNPs1 = 531 nm and ʎAuNPs2 = 534 nm; in CH2Cl2, both solutions showed ʎ = 530 nm. This displacement is one of the factors that indicated the non-aggregation of AuNPs. In DLS, non-aggregation was confirmed. In CHCl3, AuNPs1 showed transfer efficiency of 97,27% and AuNPs 98.88%, while in dichloromethane only 80,21% of AuNPs were transferred. AuNPs showed greater stability over time in CHCl3 than in CH2Cl2. After transfer to CHCl3, the AuNPs were separated from this solvent and redissolved in other organic solvents with different refractive indexes: benzyl alcohol, ethanol and dimethylsulfoxide (DMSO). The AuNPS remained visibly stable only in benzyl alcohol, because in the other solvents it was observed that the colloidal solution showed a loss of coloration and, by UV-Vis, the reduction of the LSPR band in DMSO and absence in ethanol was verified.

abstract: Solar energy is leading in renewable energy sources and the aspects surrounding the efforts to harvest light are gaining importance. One such aspect is increasing the light absorption, where heliotropism comes into play. Heliotropism, the ability to track the sun across the sky, can be integrated with solar cells for more efficient photon collection and other optoelectronic systems. Inspired by plants, which optimize incident sunlight in nature, several researchers have made artificial heliotropic and phototropic systems. This project aims to design, synthesize and characterize a material system and evaluate its application in a phototropic system. A gold nanoparticle (Au NP) incorporated poly(N-isopropylacrylamide) (PNIPAAm) hydrogel was synthesized as a photo-thermo-responsive material in our phototropic system. The Au NPs generate heat from the incident via plasmonic resonance to induce a volume phase change of the thermo-responsive hydrogel PNIPAAm. PNIPAAm shrinks or swells at temperature above or below 32°C. Upon irradiation, the Au NP-PNIPAAm micropillar actuates, specifically bending toward the incident light and precisely following the varying incident angle. Swelling ratio tests, bending angle tests with a static incident light and bending tests with varying angles were carried out on hydrogel samples with varying Au NP concentrations. Swelling ratios ranging from 1.45 to 2.9 were recorded for pure hydrogel samples and samples with very low Au NP concentrations. Swelling ratios of 2.41 and 3.37 were calculated for samples with low and high concentrations of Au NPs, respectively. A bending of up to 88° was observed in Au NP-hydrogel pillars with a low Au NP concentration with a 90° incident angle. The light tracking performance was assessed by the slope of the pillar Bending angle (response angle) vs. Incident light angle plot. A slope of 1 indicates ideal tracking with top of the pillar being normal to the incident light, maximizing the photon absorption. Slopes of 0.82 and 0.56 were observed for the low and high Au NP concentration samples. The rapid and precise incident light tracking of our system has shown the promise in phototropic applications. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2016

abstract: Proton beam therapy (PBT) is a state-of-the-art radiotherapy treatment approach that uses focused proton beams for tumor ablation. A key advantage of this approach over conventional photon radiotherapy (XRT) is the unique dose deposition characteristics of protons, resulting in superior healthy tissue sparing. This results in fewer unwanted side effects and improved outcomes for patients. Current available dosimeters are intrinsic, complex and expensive; hence cannot be used to determine the dose delivered to the tumor routinely. Here, we report a hydrogel based plasmonic nanosensor for measurements of clinical doses in ranges between 2-4 GyRBE. In this nanosensor, gold ions, encapsulated in a hydrogel, are reduced to gold nanoparticles following irradiation with proton beams. Formation of gold nanoparticles renders a color change to the originally colorless hydrogel. The intensity of the color can be used to calibrate the hydrogel nanosensor in order to quantify different radiation doses employed during treatment. The potential of this nanosensor for clinical translation was demonstrated using an anthropomorphic phantom mimicking a clinical radiotherapy session. The simplicity of fabrication, detection range in the fractionated radiotherapy regime and ease of detection with translational potential makes this a first-in-kind plasmonic colorimetric nanosensor for applications in clinical proton beam therapy. / Dissertation/Thesis / Masters Thesis Chemical Engineering 2017

IV Resumo Título: Nanoestruturas de Dissulfeto de Molibdênio: Síntese e caracterização para produção de Hidrogênio Mestrando: André Luís Silveira Fraga Orientador: Prof. Marcos José Leite Santos Palavras Chave: nanoestruturas de MoS2, nanopartículas de ouro, semicondutores, produção de hidrogênio. Neste trabalho é apresentada a síntese e caracterização de nanoestruturas de MoS2 e nanoestruturas de MoS2 decoradas com nanopartículas de ouro. O MoS2 foi obtido através de rota hidrotermal a 200 °C durante períodos de síntese de 2, 6, 12 e 24 horas. Como precursores foram utilizados molibdato de sódio, ácido 3-mercaptopropiônico, cisteamina e L-cisteína. Para avaliar o efeito da presença dos ligantes nas estruturas, as amostras de MoS2 foram tratadas térmicamente a temperaturas de 250, 550 e 750 °C, em atmosfera de argônio. Com o objetivo de avaliar o efeito da presença de nanopartículas de ouro nas propriedades fotocatalíticas do material, foi realizada a síntese in situ de nanopartículas de ouro aderidas às estruturas de MoS2. Os materiais foram caracterizados através das técnicas de difração de raios X (DRX), microscopia eletrônica de transmissão (MET), microscopia eletrônica de varredura (MEV) e espectroscopia do ultravioleta e visível (UV-Vis). As áreas superficiais e quantidade de poros foram avaliadas através das técnicas de BET (Brunauer, Emmett and Teller) e DFT (density functional theory). O precursor ácido 3-mercaptopropiônico resultou na formação de aglomerados de nanofolhas com cerca de 500 nm de diâmetro na sua maior dimensão. Ao usar cisteamina e L-cisteína foram obtidas nanoestruturas com formato de nanoflores com cerca de 300 nm de diâmetro formadas por pétalas com cerca de 30 nm. Um resultado interessante foi a rápida formação das nanoflores na presença de L-cisteína. As estruturas de nanoflores apresentaram produção de hidrogênio de até 9,6 mmol/gh. / In this work the synthesis and characterization of MoS2 nanostructures and MoS2 nanostructures decorated with gold nanoparticles is presented. The materials were obtained by hydrothermal route at 200 °C during synthesis periods of 2, 6, 12 and 24 hours. Sodium molybdate was used as Molybdenium precursor and 3-mercaptopropionic acid, cysteamine and L-cysteine as sulfur precursors. To evaluate the effect of ligands on the structures, the MoS2 samples were thermally treated at 250, 550 and 750 °C under argon atmosphere. The effect of gold nanoparticles on the photocatalytic properties of the material was evaluated by obtaining and materials with gold nanoparticle adhered to the MoS2 structures. The materials were characterized by X-ray diffraction (XRD) techniques, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and ultraviolet and visible spectroscopy (UV-Vis). The surface areas and amount of pores were evaluated using BET (Brunauer, Emmett and Teller) and DFT (density functional theory) techniques. The precursor 3-mercaptopropionic acid resulted in the formation of nano-foil agglomerates of about 500 nm in diameter. On the other hand, when using cysteamine and L-cysteine, flower-shaped nanostructures of about 300 nm in diameter formed by petals of about 30 nm were obtained. An interesting result was the rapid formation of nanoflores in the presence of L-cysteine. Nanoflower structures showed hydrogen production up to 9.6 mmol / gh.

A convergência entre a biotecnologia e a nanotecnologia tem levado ao desenvolvimento de novos nanobiocompósitos híbridos com funções sinérgicas que incorporam as propriedades de reconhecimento dos biomateriais com as propriedades eletrônicas, ópticas e catalíticas únicas das nanopartículas. Apesar do recente desenvolvimento na síntese de nanobiocompósitos, a aplicação biomédica destes materiais ainda apresenta muitos desafios, já que não apenas uma conjugação apropriada é requerida, mas também outros importantes aspectos relacionados à biocompatibilidade. O presente trabalho tem como objetivo expandir o campo da síntese e caracterização de nanoparticulas funcionalizadas com biomoléculas. Em especial, visamos o entendimento e caracterização das interações entre nanopartículas de ouro (AuNPs) e proteínas, por meio do estudo de dois sistemas distintos: AuNPs funcionalizadas com Jacalina, e AuNPs funcionalizadas com a proteína BeCen1. No primeiro sistema, o interesse advém da capacidade da lectina Jacalina de reconhecer o dissacarídeo (Galβ1-3GalNAc) associado a tumores. Neste caso, AuNPs formadas na presença do dendrímero poli(amidoamina) geração 4.0 (PAMAM G4) foram conjugadas com a Jacalina marcada com o fluóroforo Isotiocianato de fluoresceína (FITC). A formação do complexo AuNP-PAMAM G4/Jacalina foi confirmada por Microscopia Eletrônica de Transmissão (TEM), Espalhamento de Luz Dinâmico (DLS), Espectroscopia de Absorção no UV-VIS e vibracional (FTIR). A interação entre as AuNP-PAMAM G4 e a Jacalina parece ser um processo dirigido por entropia com afinidade moderada e formação de complexo, segundo os resultados de Calorimetria de Titulação Isotérmica (ITC) e supressão da fluorescência. Os resultados de Dicroísmo Circular (CD) mostraram que a conjugação da Jacalina com as AuNP-PAMAM G4 não alterou sua estrutura secundária. Testes realizados em cultura de células revelaram que o complexo apresenta maior afinidade e citotoxicidade pelas células de carcinoma do colo de útero humano (HeLa) se comparadas com fibroblastos saudáveis de adipócitos de camundongo (L929). Estes resultados são relevantes uma vez que demonstram o potencial do complexo AuNP-PAMAM G4/Jacalina-FTIR para aplicações biomédicas incluindo diagnóstico e tratamento de câncer. O segundo sistema é interessante devido a habilidade da proteína BeCen1 em formar filamentos nanométricos em função da temperatura. As AuNPs foram formadas na presença da proteína utilizando ácido fórmico diluído como agente redutor e o excesso de proteína foi separado por Cromatografia de Exclusão Molecular. Análises de CD revelaram uma pequena diminuição no conteúdo de α-hélices, confirmado por FTIR, o que pode estar relacionado à interação das AuNPs com os grupamentos amida desta proteína. Medidas de espalhamento de luz revelaram um aumento da turbidez da suspensão do complexo AuNP-BeCen1 com o aumento da temperatura e imagens de TEM, com e sem aquecimento, confirmaram uma mudança de padrão no arranjo das AuNPs. Estes resultados revelam a possibilidade de fabricação de nanobiocompósitos termorresponsivos, o que pode ser muito importante para aplicações em nanodispositivos. / The convergence between biotechnology and nanotechnology has led to the development of new hybrid nanocomposites that conjugate the bio-recognization properties of biomaterials and the unique electronic, optic and catalytic properties of the nanoparticles. Despite the recent advances in the development of nanobiocomposites, the biomedical applications of these materials are still limited, among other factors, by the low efficiency of functionalization and biocompatibility. The present study was aimed at developing proteinconjugated nanoparticles for application in nanomedicine. Our main focus were the understanding and characterization of the interactions between proteins and gold nanoparticles (AuNPs), which was accomplished using two distinct systems, viz.: Jacalin-functionalized AuNPs, and Becen1-functionalized AuNPs. In the former, the interest is due the capability of the protein Jacalin of recognize the disaccharide (Galβ1-3GalNAc), largely expressed in some tumors cells. AuNPs were synthesized in the presence of the polyamido amine generation 4.0 (PAMAM G4) and conjugated with a Jacalin target with the fluorescein isothiocyanate (FITC). The excess of protein was removed by centrifugation and the complex formation was confirmed by Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS), UV-VIS Absorption and Vibrational Spectroscopy (FTIR). The interactions between AuNP-PAMAM G4 and Jacalin seemed to be driven by an entropic process with moderate affinity and complex formation, as revealed by Isothermal Titration Calorimetry (ITC) and quenching fluorescence measurements. Furthermore, Circular Dichroism (CD) analyses revealed that protein maintained its secondary structure upon conjugation with the nanoparticles. In vitro tests revealed that the AuNPs/Jacalin complexes presented higher affinity and cytotoxicity against human cervical cancer cell (HeLa) compared to healthy mouse fibroblasts (L929). These results are relevant, since the AuNP-PAMAM G4/Jacalin-FITC complex may be used for biomedical applications including cancer treatment and diagnostics. The second nanocomplex, comprising AuNPs and BeCen1, was chosen due to the ability of BeCen 1 to polymerize in the form of nanometric filaments as a function of temperature. The AuNPs were formed in the presence of the protein using diluted formic acid as reducing agent and the excess of protein was removed by Molecular Exclusion Chromatography. CD analysis showed a decrease in the -helix structures confirmed by FTIR, which may be related to the interaction between the AuNPs and the amide groups of the protein. Light scattering measurements revealed an increase in the turbidity of the dispersions upon increasing the temperature, indicating a change in the arrangement of the AuNPs. Such BeCen-1 induced alignment was confirmed by TEM images. The latter results point to the possibility of fabrication of novel thermoresponsive nanobiocomposites, which are of great relevance for nanodevices applications.

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.

Philosophiae Doctor - PhD / Ovarian cancer is called the “Silent Killer” as it is often diagnosed in advanced stages of the disease or misdiagnosed which ends with a poor prognostic outcome for the patient. A high rate of disease relapse, a high incidence-to-mortality ratio as well as acquired multidrug resistance makes it necessary to find alternative diagnostic- and therapeutic tools for ovarian cancer. Nanotechnology describes molecular devices with at least one dimension in the sub- 1μm scale and has been suggested as a possible solution for overcoming challenges in cancer multidrug resistance as well as early diagnosis of the disease. One-pot synthesized gold nanoparticles were used to demonstrate in vitro drug delivery of doxorubicin in a manner which overcame the cytoprotective mechanisms of a multidrug resistant ovarian carcinoma cell line (A2780cis) by inducing apoptosis mediated by caspase-3 within 3h of treatment. The gold nanoparticles were further functionalized with nitrilotriacetic acid and displayed specific interaction with a 6xHis-tagged cancer targeting peptide, chlorotoxin. Proprietary indium based quantum dots were functionalized with the same surface chemistry used for gold nanoparticles and bioconjugated with chlorotoxin. Wide field fluorescence studies showed the peptide-quantum dot construct specifically targeted enhanced green fluorescent tagged matrix metalloproteinase-2 transfected A2780cis cells in a specific manner. The cytoprotective multidrug resistant mechanisms of the ovarian carcinoma was overcome successfully with a single dose of doxorubicin loaded gold nanoparticles and tumour specific targeting was demonstrated using quantum dots with a similar surface chemistry used for the gold nanoparticles.

Botrytis species affect over 300 host plants in all climate areas of the world, at both pre and post-harvest stages, leading to significant losses in agricultural produce. Therefore, the development of a rapid, sensitive and reliable method to assess the pathogen load of infected crops can help to prescribe an effective curing regime. Growers would then have the ability to predict and manage the full storage potential of their crops and thus provide an effective disease control and reduce post-harvest losses. A highly sensitive electrochemical immunosensor based on a screen-printed gold electrode (SPGE) with onboard carbon counter and silver / silver chloride (Ag/AgCl) pseudo-reference electrode was developed in this work for the detection and quantification of Botrytis species. The sensor utilised a direct sandwich enzyme-linked immunosorbent assay (ELISA) format with a monoclonal antibody against Botrytis immobilised on the gold working electrode. Two immobilisation strategies were investigated for the capture antibody, and these included adsorption and covalent immobilisation after self-assembled monolayer formation with 3-dithiodipropionic acid (DTDPA). A polyclonal antibody conjugated to the electroactive enzyme horseradish peroxidase (HRP) was then applied for signal generation. Electrochemical measurements were conducted using 3,3’, 5,5’-tetramethylbenzidine dihydrochloride / hydrogen peroxide (TMB/H2O2) as the enzyme substrate system at a potential of -200 mV. The developed biosensor was capable of detecting latent Botrytis infections 24 h post inoculation with a linear range from 150 to 0.05 μg fungal mycelium ml-1 and a limit of detection (LOD) as low as 16 ng ml-1 for covalent immobilisation and 58 ng ml-1 for adsorption, respectively. Benchmarked against the commercially available Botrytis ELISA kits, the optimised immuno-electrochemical biosensor showed strong correlation of the quantified samples (R2=0.998) ... [cont.].

Philosophiae Doctor - PhD / Obesity is a complex metabolic disease of excessive fat accumulation. It is a worldwide epidemic affecting billions of people and its pharmacological management is hampered by drug toxicity and undesirable side effects. Therefore, a need still exists for the development of safe medication for treatment of obesity. Nanotechnology involves the use of small particles at atomic and molecular scale. It has application in medical diagnostics, drug delivery and molecular imaging. Various nanoparticles (NPs) functionalized with different biomolecules have been successfully used in many therapeutic and research applications due to their versatility, ease of chemical synthesis, low toxicity and unique properties. Examples of NPs used in this study are Gold nanoparticles (GNPs) and Quantum dots (QDs). GNPs and QDs are extensively used as drug delivery, labelling and imaging tools in biomedical research. Nanotechnology offers a new potential useful avenue for solving the problem of toxicity of anti-obesity drugs. This could be achieved through targeted drug delivery. In this study, rats were fed a high fed diet (HFD) to induce obesity. The streptavidin conjugated GNPs and QDs were functionalized with biotinylated adipose-homingpeptide (AHP) and/or anti-obesity drug (Gallic acid). Functionalization was characterized using agarose gel electrophoresis, UV-vis spectroscopy and transmission electron microscopy. The binding-specificity and targeting ability of AHP was evaluated in vitro and in vivo. The apoptotic effect of AHP functionalized-drug loaded GNPs (AHP-GA-GNPs) was tested in vitro using APOPercentage TM and Caspase-3 activation assays. The in vitro data indicated that the binding was specific to prohibitin (PHB) expressing cells (MCF-7 and Caco-2), and that the binding was temperature dependent. PHB was confirmed as a target for AHP after overlaying AHP-FITC and anti-prohibitin antibody staining. Cellular uptake was detected on the cells treated with AHP-functionalized NPs as compared to unfunctionalized NPs. The GA and AHP-GA-GNPs reduced cellular viability and induced apoptosis through activation of Caspase-3. The Ex-vivo studies using primary endothelial cells (ECs) isolated from the WAT of lean and obese Wistar rats showed that the binding of AHP was receptor mediated, and specific to receptors differentially expressed in ECs from obese WAT. The in vivo studies showed that, treatment of obese rats with AHP-functionalized NPs resulted in targeted delivery of the NPs to the WAT as compared to those treated with unfunctionalized NPs. Qualitative analysis using fluorescence microscopy and IVIS Luminar XR, live-imaging system showed that the unfunctionalized NPs accumulated mostly in the organs of the reticuloendothelial system, namely: liver, spleen, lungs and kidneys. In contrast, AHP-functionalized NPs accumulated mostly in the WATs as compared to the rest of the organs of the obese rats. Uptake and binding of the NPs to the tissues was quantitatively confirmed by the inductive coupled plasma-optical emission spectroscopy (ICP-OES). In conclusion, this study reports the 1) successful functionalization of GNPs and QDs with AHP, 2) use of AHP-functionalized GNPs and QDs as delivery and imaging agents to the WAT, and 3) potential use of AHP-functionalized drug-loaded GNPs in the treatment of obesity.