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This thesis presents investigations into the design and synthesis of nanomaterials in supercritical carbon dioxide (sc-CO₂) as well as novel experimental design methodologies. First, the process-structure-property relationships are studied for the deposition of materials from organometallic precursors in sc-CO₂. The materials that were investigated in these studies were: (1) the semiconductor material copper zinc tin sulfide (Cu₂ZnSnS₄, or CZTS), which has application in solar energy capture; (2) zinc sulfide nanoparticles deposited onto carbon nanotubes, which have application in optoelectronics; and (3) silver nanoparticles deposited on silicon and glass wafer surfaces, which find application as biosensors via surface enhanced Raman spectroscopy. Next, two novel experimental design methodologies were implemented. The first is termed layers of experiment with adaptive combined design (LoE/ACD), which efficiently optimizes a process that is expensive and time consuming to study by zooming in on the process optimum through successive layers. The mean silver nanoparticle size was optimized as a function of temperature in the sc-CO₂ system using the LoE/ACD approach. The second experimental design methodology is called initial experimental design (IED). The IED methodology was developed to choose the first round of experiments for a system that is expensive to study (in terms of time and money), poorly understood, and possesses a related, non-identical system that is well-studied. The IED approach was used to optimize the mean iridium nanoparticle size as a function of temperature given expert opinion, prior data, and an engineering model for silver nanoparticles synthesized in sc-CO₂.

Suspended titanium dioxide (TiO2) nanoparticles produce hydroxyl radicals (•OH) that synergistically aid in disinfection when irradiated with UV light. To exploit the benefits of TiO2 photocatalysis without having to remove them, TiO2 was deposited onto 3M Company’s nanostructured thin film (NSTF). •OH production by suspended and TiO2-NSTF was determined by para-chlorobenzoic acid (pCBA), a •OH probe compound. Both techniques of introducing TiO2 to the samples produced equivalent •OH without forming bromate, a regulated byproduct in drinking water at all UV and TiO2 levels. Formation of bromate by ozone in brackish water and seawater were used to compare the disinfection byproduct (DBP) formation between the disinfection methods. Additionally, monitoring bromate, typically performed by ion chromatography, is complicated by chloride and other anions present in brackish water or seawater. Thus, a spectrophotometric method to measure bromate in saline systems is introduced.

This thesis presents the development of novel methodologies in the template mediated chemical synthesis of lariat and branched nucleic acids. The synthetic branched DNA and RNA may be applicable as probes in the elucidation of the splicing mechanism or as potential therapeutic agents. Furthermore, this body of work describes the novel synthesis of Ru(II) branched DNA as building blocks in the supramolecular assembly of nano-motifs. In general, insight into the utilization of nucleic acids as biological molecules and as nanomaterials is presented at the interface of chemistry and biology. / Chapter 2 delineates the regioselective template directed synthesis of Y-RNA via chemical ligation at the branch point of a 5'-phosphate to a 2'-hydroxyl. The branched molecules resemble lariats as they possess the analogous branched architecture. The oligonucleotide components are synthesized from commercially available phosphoramidite building blocks through automated solid-phase synthesis. A unique template directed method in the synthesis of DNA and RNA lariats is proposed in Chapter 3. The regioselective chemical ligation affords wild-type DNA and RNA formed through assembly of a single oligonucleotide strand. A parallel DNA:RNA hybrid association was observed in the preorganized assembly and extensively characterized. Characterization of the Y-RNA and lariat nucleic acids were carried out through techniques such as thermal denaturation analysis, polyacrylamide gel electrophoresis, enzymatic degradation with the RNA lariat debranching enzyme, alkaline treatment as well as MALDI-TOF mass spectrometry. / The second part of the thesis exploits DNA as a nanomaterial in the convergent solid-phase synthesis of Ru(II)-DNA conjugates as branched building blocks in the assembly of nanostructures. Chapter 4 describes the synthesis of Ru branched DNA, utilizing cis-[(bpy)2Ru(imidazole) 2]2+ moiety as the vertex tethered to parallel DNA covalently through flexible hexamethylene linkers. Complete physical characterization and preliminary hybridization studies are conducted. The Ru-DNA conjugates presented were found to be unstable to the protocols required for synthesis of mixed sequence derivatives. The stability and scope of synthesis of these molecules are further discussed. / As an alternative, Ru-DNA branched complexes of mixed sequences, exhibiting greater stability, were synthesized. The transition metal building blocks of Chapter 5 employ a more rigid branch point, linking two parallel DNA strands through a one methylene spacer to the cis-[Ru(bpy)2 (4,4'-bis(hydroxymethyl)-2,2'-bipyridine)][PF6]2 vertex. Physical characterization and the intrinsic luminescent properties of the transition metal complex were confirmed in both the Ru-branched DNA and hybrized forms. A comparative study of the self-assembly behavior of the Ru-DNA conjugates to that of unmetallated branched DNA was also conducted. Interestingly, results indicate a metal-mediated assembly of almost exclusive formation of one discrete Ru-DNA dimeric cyclic nanostructure, where as unmetallated DNA building blocks produced an array of products. Complete confirmation of these products is presented through PAGE and enzymatic digestions. Finally the synthesis of novel Delta and Λ Ru-branched DNA diastereomers is presented as potential building blocks in the creation of chiral metallo-supramolecular constructs.

<p>The main aim of this study was to develop a novel strategy for harnessing the properties of electroconductive polymers in sensor technology by using polymeric nanostructured blends in the preparation of high performance sensor devices.</p>

Silver nanoparticles (AgNP), the most popular nano-compounds, possess unique chemical, physical and biological properties. Albizia adianthifolia (AA) – rich in saponins – is a plant of the Fabaceae family, found abundantly on the East coast of Africa. This plant is well known for its medicinal properties, and although the exact phytochemistry of AA is unknown, recent research suggests that AA can be used for the treatment of certain pathologies. The biological properties of a novel silver nanoparticle (AAAgNP) synthesised from an aqueous leaf extract of AA, were investigated on A549 lung carcinoma cells. Cell viability was determined by the 3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assay. Cellular oxidative status (lipid peroxidation and glutathione (GSH) levels) were determined by the TBARS and GSH-Glo™ Glutatione assays respectively. ATP concentration was measured using the CellTitre-Glo™ assay. Caspase-3/-7, -8 and -9 activities were determined by Caspase-Glo® assays. Flow cytometry was used to measure apoptosis, mitochondrial (mt) membrane depolarisation, expression of CD95 receptors and intracellular smac/DIABLO levels. DNA fragmentation was assessed with the comet assay. The expression of p53, bax, PARP-1 and smac/DIABLO was evaluated by western blotting. Quantitative polymerase chain reaction was used to determine mRNA levels of bax and p53. AAAgNP caused a dose-dependent decrease in cell viability with a significant increase in lipid peroxidation (5-fold vs. control; p=0.0098) and decreased intracellular GSH (p=0.1184). A significant 2.5-fold decrease in cellular ATP was observed upon AAAgNP exposure (p=0.0040) with a highly significant elevation in mt membrane depolarisation (3.3-fold vs. control; p<0.0001). Apoptosis was also significantly higher (1.5-fold) in AAAgNP treated cells (p<0.0001) with a significant decline in expression of CD95 receptors (p=0.0416). AAAgNP caused a significant 2.5-fold reduction in caspase-8 activity (p=0.0024) with contrasting increases in caspase-3/-7 (1.7-fold vs. control; p=0.0180) and -9 activity (1.4-fold vs. control; p=0.0117). Western blots showed increased expression of smac/DIABLO (4.1-fold) in treated cells (p=0.0033). Furthermore, AAAgNP significantly increased the expression of p53, bax cleaved PARP-1 (1.2-fold; p=0.0498, 1.6-fold; p=0.0083 and 1.1-fold; p=0.0359 respectively). The expression of mRNA for both p53 and bax was also elevated post AAAgNP treatment, with 6-fold (p=0.0036) and 5-fold (p=0.0080) changes respectively compared to untreated cells. Data suggests that AAAgNP induces cell death in the A549 lung cells via the mt-mediated intrinsic apoptotic program. Further investigations are required to assess the potential use of AAAgNP in cancer treatment. / Thesis (M.Med.)-University of KwaZulu-Natal, Durban, 2012.

The development of electronics has been growing at a fast rate in recent years. More and more ideas have been searched and are increasing at a faster rate. However, there is more detail work in the nanolevel or nanostructure yet to be understood. Thus, more and more semiconductor physicists have move to the new field of study in nanostructures. Nanostructures are the future of electronic devices. By understanding nanostructure electronic devices, electronics is the key for the progress of any modern equipment and advancement. This comes about when electronic transport of a nanostructure is thoroughly understood. Thus, future electronic devices can utilize the development of conductance through components having dimensions on the nanometer scale.The objective of the proposed research project is to study electronic transport in a ring with an infinite potential barrier at the center and a modulated external potential in one of the arms. The relative phase between the two paths in this structure can be controlled by applying electrostatic potential in one of the arms. One can compare these types of systems with optical interferometers, where the phase difference between the two arms is controlled by changing the refractive index of one arm through the electro-optic effect. By modulating the potential in one arm of the ring, we will study the interference effect on conductance. The method of finding the conductance of a nanostructure will be using the recursive Green's function method. This includes finding transverse eigenvalues, eigenfunctions, and hopping integrals to determine Green's propagators. A FORTRAN 77 computer program is used for numerical calculations.These remarkable ultra-small and ultra-clean quantum systems are currently achieved due to significant technological advancement in fabrication. For ultra-small quantum devices, the theoretical understanding of device performance must be based on quantum carrier transport of confined electrons and holes in the channel. This theoretical research will lead to the understanding of the effects of geometry and impurities on transport of the carriers in the nanochannels. / Department of Physics and Astronomy

The synthesis, structure and physical properties of a series of Mnx(Co, Mg)₁ˍxFe₂O₄, (Mg, Sr)₀.₂ Mn₀.₁Co₀.₇Fe₂O₄ and Mg₀.₅Mn₀.₅(RE)₀.₁Fe₁.₉O₄ (where RE are rare earth elements) nanoferrites have been studied. These compounds were synthesized at low reaction temperature of about 200 ⁰C using the glycol-thermal method. The starting materials were high-purity metal chlorides or nitrates which were precipitated by NH₄OH and KOH respectively. In addition, MnxCo₁₋xFe₂O₄ (x = 0, 0.5 and 1) samples were produced directly from high-purity metal oxides by high-energy ball milling technique. Single-phase cubic spinel structure and nanoparticle structure of the synthesized samples were confirmed by X-ray diffraction (XRD) and transmission electron microscope (TEM). The results show that the produced powders of the asprepared samples have average grain sizes ranging from 7 to 16 nm. Filtering the precipitates by Whatman glass microfiber filters (GF/F) appears to be important in obtaining the small particle sizes. We suspect higher stability of the MnxCo₁₋xFe₂O₄ at x = 0 and 0.5 where complete symmetry in the proportion of the atoms on tetrahedral (A) and octahedral (B) sites would tend to favour larger nanoparticles. The evolutions of the magnetic properties as a function of composition, annealing temperature under air and argon atmospheres or measuring temperature have been investigated by ⁵⁷Fe Mössbauer spectroscopy, vibration sample magnetometer (VSM) and superconducting quantum interference device (SQUID). Significant changes in magnetic properties are observed across the composition ranges studied. The Mössbauer spectra indicate ferrimagnetic, superparamagnetic and paramagnetic behaviours of the compounds. The results show evidence of transformation from single-domain to multi-domain structure with thermal annealing in our samples. Temperature dependence of magnetization shows differences between field cooling (FC) and zero field cooling (ZFC) which we attribute to spin-freezing and thermal relaxation for typical nanoparticles. Significant increase in coercive field with reduction in measuring temperature is obtained in Co- based compounds. Mn₀.₅Co₀.₅Fe₂O₄, Sr₀.₂Mn₀.₁Co₀.₇Fe₂O₄ and Mg₀.₂Mn₀.₁Co₀.₇Fe₂O₄ have large coercive fields of 1.45, 3.02 and 10.70 kOe at 4 K compared to 0.17, 0.05 and 0.05 kOe at room temperature respectively. Variation of coercive fields (Hc) with measuri ing temperature for MnxCo₁₋xFe₂O₄ (x = 0.1 and 0.05), (Mg, Sr)₀.₂Mn₀.₁Co₀.₇Fe₂O₄ nanoferrites follow the Kneller's law for uniaxial non-interacting single domain particles of the form Hc(T) = Hc(0)[1-( T/Tβ)α]. The observed temperature dependences are consistent with α = 1/2. We also find evidence of the departure from this law at lower temperature. The temperature dependence of the saturation magnetizations were observed to vary with temperature according to the modified Bloch's law Ms(T) = Ms(0)[1 - ( T/T₀)ᵝ] where β is at least 1.5. This is attributed to the confinement effects of the spin-wave spectrum for magnetic clusters. The equation appears to fit the saturation magnetization data over the entire temperature range with values of β from 2.1 to 2.4 for the samples studied. These results are consistent with the nanoparticle nature of the compounds. In Mg₀.₅Mn₀.₅(RE)₀.₁Fe₁.₉O₄ nanoferrites, the grain sizes, lattice parameters and saturation magnetizations increase with RE substitution which we attribute to larger RE ions substituting smaller Fe ions. The results show evidence of superparamagnetic behaviour of the nanoparticles. The highest grain size and magnetizations are obtained for the Gd substituted sample. We find strong correlation between the saturation magnetizations, grain sizes and microstrains with de Gennes factor G. The correlation with grain sizes and microstrains appear to be unique and characteristic of the nanoparticle nature of the compounds. Bulk samples in the form of pellets were also produced from the as-prepared samples of MnxCo₁₋xFe₂O₄ for resistivity measurements. The temperature dependence of the electrical resistivity for samples sintered from 600 - 1100 ⁰C under argon atmosphere were studied using the four-probe method from room temperature to about 110 ⁰C. Two possible mechanisms for resistivity involving Tˉ¹ and Tˉ¹/² dependences were investigated which we associated with semiconducting and inter-grain conductivity respectively. The Tˉ¹/² dependence is found to fit the data better and predicts higher activation energies. The resistivity was observed to be sensitive to the surface of the pellet being probed and the annealing temperature. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2012.

A novel way of producing nanostructures in the past decade has been through the use of an anodized alumina template. This template has dense, self-ordered nanometric pores that grow in the oxide as the aluminum is being anodized. This technique is a fairly new method of processing nanostructures, and much study and research is presently being done to understand the formation mechanisms of the highly ordered pores. Ultra-pure aluminum foil and pure aluminium single crystal plates were anodized to create porous anodized alumina, and using it as a template to electro-deposit Nickel nanostructures. The effects different anodizing parameters have on oxide creation were studied, and the results obtained from studying the effects of substrate purity and texture of the anodized aluminum substrate on the morphology of the alumina template, through the use of X-ray diffraction and scanning electron microscopy. / Nickel nanowires were prepared by DC electrodeposition inside the porous alumina template with a gold-palladium coating serving a conductive base. The nanowires have a diameter of 65 nm, and their length depends on the deposition time. The nanowires can uphold a position perpendicular to the substrate by partially dissolving the alumina template. They also have a tendency to gather together once the template is partially removed.

A very interesting class of nanoparticles extensively used for bio-applications is that of hydrogel particles, also called nanogels. There is an increasing interest in the design of hydrogel nanoparticles that have biofunctionality for applications in cell targeting, drug delivery, and biomedicine. The dissertation focuses on developing synthetic strategies for making diverse hydrogel nanoparticles customized to have desirable properties for various bio-applications. We have also investigated the potential of such nanoparticles as coatings for biomedical implants. Chapter 1 gives a brief introduction to hydrogel nanoparticles and the properties that make them attractive for various applications. The details of the syntheses of well defined, stable nanoparticles, commonly used in literature, are described in Chapter 2. Chapter 3 describes our synthesis of hollow sub-50 nm nanogels, which are otherwise difficult to synthesize based on the strategy discussed in Chapter 2. Chapter 4 also demonstrates how simple strategies borrowed from organic chemistry help in producing nanogels with multiple functionalities that are otherwise difficult to obtain, which also is an important advance over the synthetic methods discussed in Chapter 2. Chapter 5 describes how a general strategy based on photoaffinity labeling can yield materials with many applications ranging from optical materials, drug delivery, to biosensing. The latter part of the dissertation describes applications of various nanogels in biology especially as coatings that can control inflammation caused by biomaterials. Chapter 6 describes a method to functionalize flexible biomaterials with the nanogels, thus enabling in vivo investigations of the nanogels as potential coatings for controlling inflammation. Chapter 7 describes the biological studies performed (in collaboration with Garcia Group in the School of Mechanical Engineering at Georgia Tech) on various nanogels, aimed towards obtaining the most functional and efficient materials for implant applications. Chapter 8 describes application of hollow nanogels for covalently immobilizing biomolecules. This chapter also demonstrates how simple non-functional materials can be made unique and functional by means of traditional organic reactions. Finally, in order to broaden the applications of nanogel based materials.