Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

There is significant interest in applying nanoparticle (NP) science to subsurface reservoirs to facilitate oil and gas recovery, image subsurface reservoirs, aid sequestration of CO2 and benefit environmental remediation. Imaging nanoparticles have been designed with long-term dispersion stability in brine and minimal retention in reservoir rock and with preferential adsorption at oil-water interfaces. Polymer-stabilized nanoparticles provide sufficient electrostatic repulsion for high colloidal stability, as characterized by the zeta potential. The small size of the clusters, superparamagnetic properties, and high salt tolerance are highly beneficial in various applications including magnetomotive and electromagnetic imaging and mapping of petroleum reservoirs. Superparamagnetic nanoclusters may be used in imaging in biomedicine and in mapping of petroleum reservoirs, by generating either ultrasonic or acoustic signals with oscillating magnetic motion. For a given magnetization per weight of iron oxide, nanoclusters with sub ~100 nm diameters experience a much larger magnetic force than that of the primary sub- 10 nm primary particles. Aqueous dispersions of 0.1-0.2 wt% superparamagnetic iron oxide nanoclusters were stabilized with citric acid, poly(acrylic acid) (PAA), or poly(styrene sulfonate-alt-maleic acid) (PSS-alt-MA) on the particle surface, with a high loading of ~90% iron oxide. For nanoclusters with only 12% (w/w) PSS-alt-MA electrosteric stabilization was sufficient even in 8 wt% NaCl. Both PAA and PSS-alt-MA were used to stabilize nanoclusters with controlled size during synthesis in aqueous media. To obtain a permanent coating on the surface of clusters cross-linking of the polymer for different cross-linking densities was applied. In this general and highly flexible approach, iron oxide nanoparticles may be formed with an adsorbed polymer stabilizer, which is then permanently bound to the surface via cross-linking. To investigate interfacial activity of nanoparticles, oil-in-water emulsions were stabilized with iron oxide nanoclusters or graphene oxide platelets. In each case, the stabilization was achieved by designing the hydrophilic/hydrophobic nature of surface coating. For oil/water emulsions, the droplet size was as low as ~1 micron diameter, and strongly shear-thinning rheology was observed. A series of sub-100 nm superparamagnetic iron oxide nanoparticles with amphiphilic poly(acrylic acid-b-butylacrylate), (PAA-b-PBA) copolymer shells was synthesized to investigate the effect of the polymer structure on the interfacial tension for nanoparticles adsorbed at the dodecane-water interface. Large reductions in interfacial tension of up to 27.6 mN/m were obtained for a 0.27 wt% nanoparticle concentration indicating significant nanoparticle adsorption and interaction with the oil and water molecules at the interface. The adsorption energy of the polymer-coated nanoparticles at the dodecane/water interface was determined from the interfacial tension and nanoparticle radius, and analyzed in terms of the structure of the polymer stabilizer. Furthermore, oil-in-water emulsions stabilized with graphene oxide nanoplatelets were found to remain stable for several months even at high salinity (up to 5 wt% NaCl, for pH = 2 to 10). The droplet sizes were as small as ~1 μm with a low nanoplatelet concentration of 0.2 wt%. / text

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Organic solar cells (OSCs) have shown great promise in becoming the next generation of renewable energy due to its low cost, simple manufacturing process and flexibility. A method of efficiency improvement in OSCs is by incorporating metallic nanoparticles (NPs). While various reports have reported that incorporation of NPs improve OSC efficiencies due to the Localized Surface Plasmon Resonance (LSPR) effect, the investigations have lacked depth and a detailed investigation is necessary to fully understand the device mechanisms of these OSCs. In this thesis, we first investigate OSCs incorporating Au NPs into the hole collection Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) layer. Our theoretical and experimental results show that the very strong near field around Au NPs due to LSPR mainly distributes laterally along the PEDOT:PSS rather than vertically into the adjacent active layer, leading to minimal enhancement of light absorption in the active layer. With optical effects proven to be minor contributors to device performance improvements, we investigate the electrical properties of the OSCs and obtain insights into the detailed device mechanisms. Improvements in power conversion efficiency (PCE) of solar cells are found to originate from the enlarged active layer/PEDOT:PSS interfacial area and improved PEDOT:PSS conductivity. At high NP concentrations, reduced exciton quenching at donor/acceptor junctions is found to cause PCE deterioration. Next, the effects of Au NPs incorporated into the active layer of OSCs with a newly synthesized donor polymer are investigated in detail. Our experimental and theoretical results both show that LSPR introduced by the NPs can enhance the light absorption in the active layer of OSCs because the strong LSPR near field mainly distributes laterally along the active layer. Combined with our previous study, our results strongly suggest that NPs have to be incorporated in the active layer in order to harvest light by the LSPR effect. Meanwhile, our results show that the electrical properties of NPs improve at low concentration of NPs. When NP concentration is increased, the electrical properties deteriorates and counter-diminish the optical enhancement from LSPR and reduces the overall performance improvement. Finally, we demonstrate efficiency improvement in OSCs by ~22% through incorporating Au NPs into all polymer layers. Au NPs are found to have distinct mechanisms in improving device performance when incorporated in different polymer layers. Our results indicate that the efficiency improvement is the accumulated effects of incorporating NPs in the individual layers and that coupling is not observed in this device configuration. On the whole, our findings highlight the importance that both optical and electrical properties need to be studied and optimized simultaneously for achieving enhancement in PCE of OSCs. We have carried out a detailed study on incorporating NP in various layers and our results are highly useful for the design of high efficiency OSCs incorporating metallic NPs. / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Malaria is an infectious disease caused by eukaryotic protists in the genus Plasmodium. Approximately half of the world's population is at risk of malaria. The burden of Plasmodium falciparum malaria has increased in recent years due to the emergence of resistant strains, which have even been documented in regions previously reported as malaria-free. Although malaria vaccine research has been conducted and has showed recent positive results, there still remains no effective vaccine to prevent malaria in clinical practice. According to the World Health Organization, prompt confirmation of malaria infection by microscopy and/or rapid diagnostic test (RDT) is critical to control the spreading of malaria and to prevent the evolution of drug resistant Plasmodia strains. However, malaria diagnosis remains a significant challenge as many malaria endemic regions have inadequate access to microscopy, and antibody-based RDTs are restricted by their stability under tropical temperatures and by their cost. The objective of this study was to develop a new approach to malaria diagnosis using DNA aptamers to recognise proteins encoded by Plasmodium. The research is divided into two parts. Firstly, DNA aptamers against the diagnostic markers, P. falciparum histidine-rich protein 2 (HRP2) and P. falciparum lactate dehydrogenase (PfLDH), were selected by Systematic Evolution of Ligands by Exponential Enrichment (SELEX). Secondly, a selected PfLDH aptamer was incorporated into a gold nanoparticle detection system to develop an aptamer-nanoparticle conjugate as a new approach towards malaria diagnosis. The identified HRP2 and PfLDH aptamers were characterised by isothermal titration calorimetry (ITC) for their affinity to targets and were observed to bind with nanomolar affinity. As PfLDH aptamers were observed to have a higher affinity to their target, PfLDH, their specificities were further characterised by ITC using human lactate dehydrogenases, hLDHA1 and hLDHB. The PfLDH aptamers were shown to be highly specific to PfLDH with no observed affinity to human LDHs. After further characterisation, PfLDH aptamer 2008s was chosen for the next stage of the research to be combined with a nanoparticle as a route towards diagnostic application. In the second part of this study, PfLDH aptamer 2008s was conjugated to gold nanoparticles (AuNPs) to create aptamer-AuNP conjugates (2008s-AuNP). The aptamer-AuNP conjugates were characterised by their tolerance in different pH and salt concentration and in their sensitivity to PfLDH. This new approach of malaria diagnosis was further validated by incubating the aptamer-AuNP conjugates with various proteins and colour changes were observed specifically upon incubation with PfLDH but not with other proteins. Hence, a Plasmodium specific aptamer-AuNP conjugate to the malaria diagnostic marker, pLDH, has been developed in this research. This work lays the foundation for further development of novel rapid diagnostic tests based on nucleic acid aptamers and nanotechnology for robust and cost-effective malaria diagnosis with potential benefit not only for malaria but in a plethora of diagnostic applications. / published_or_final_version / Biochemistry / Doctoral / Doctor of Philosophy

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