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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
471

Control of structure and function of block copolymer nanoparticles manufactured in microfluidic reactors: towards drug delivery applications

Xu, Zheqi 26 April 2016 (has links)
This thesis includes three studies on related aspects of structure and function control for drug delivery block copolymer nanoparticles manufactured in segmented gas-liquid microfluidic reactors. First, the self-assembly of a series of photoresponsive poly(o-nitrobenzyl acrylate)-b-polydimethylacrylamide copolymers is conducted in the gas-liquid segmented microfluidic reactor at various flow rates. The resulting morphologies are found to be flow-variable and distinct from nanoparticles prepared off-chip by dropwise water addition. Photocleaving of the nanoparticles formed at different flow rates reveal flow-variable photodissociation kinetics. Next, we conduct a direct comparison between a commercially-available single-phase microfluidic mixer and the two-phase, gas-liquid segmented microfluidic reactor used in our group, with respect to nanoparticle formation from a typical block copolymer identified for drug delivery applications, polycaprolactone-b-poly(ethylene oxide). The two-phase chip yields morphologies and core crystallinities that vary with flow rate; however, the same parameters are found to be flow-independent using the single-phase mixer. This study provides the first direct evidence that flow-variable structure control is a unique feature of the two-phase chip design. Finally, we investigate structure and function control for paclitaxel (PAX)-loaded nanoparticles prepared from a series of poly(6-methyl caprolactone-co-ε-caprolactone)-block-poly(ethylene oxide) copolymers with variable 6-methyl caprolactone (MCL) content. For all MCL-containing copolymers, off-chip preparations form nanoparticles with no measurable crystallinity, although PAX loading levels are higher and release rates are slower compared to the copolymer without MCL. Both off-chip and on-chip preparations yield amorphous spheres of similar size from MCL-containing copolymers, although on-chip nanoparticles showed slower release rates, attributed to more homogeneous PAX distribution due to faster mixing. / Graduate
472

Core-Shell Nanoparticles: Synthesis, Design, and Characterization

Carroll, Kyler 12 July 2010 (has links)
The design of core/shell nanoparticles is of great interest for a wide range of applications. The primary focus of this dissertation is on the design and optimization of two synthetic routes. The first one is an aqueous reduction method using sodium borohydride and sodium citrate. This method was extended to design two types of core/shell nanoparticles, both of which have many applications in bio-sensing, magnetic resonance imaging, and magnetically guided SERS for the identification of environmental threats. The first, Fe/Ag core/shell nanoparticles were designed using a novel one-pot method by varying the AgNO3 addition time in the system. For example, if AgNO3 is added five minutes after the start of the reaction, the already formed Fe nanoparticles serve as seeds for heterogeneous nucleation and growth of Ag nanoparticles. The result of the synthesis was 50 nanometer spherical particles with a narrow size distribution. The second type, Fe/SiO2/Au core/shell nanoparticles were designed using a two-step method. First, 150 nanometer spherical Fe nanoparticles were synthesized followed by the addition of tetraethylorthosilicate (TEOS). This created a Fe/SiO2 core/shell nanoparticle to which HAuCl3 was added. In both cases, Fe/Ag and Fe/SiO2/Au, the formed nanoparticles were characterized and tested for the application as SERS active materials. The second part of this dissertation work was focused on using the polyol method to design bimetallic Cu/Ni, Fe/FeOx, and Co/C core/shell nanoparticles. In each case, the polyol method provided an easy one-pot reaction to synthesize these novel nanomaterials. The design of the Cu/Ni nanoparticles allowed for further insight into the polyol mechanism by independently investigating the factors that govern the formation of elemental Cu and Ni nanoparticles. By understanding the ability of the polyols to easily prepare metal and metal oxide nanoparticles, we were able to manipulate a one-pot reaction to design an aqueous ferrofluid consisting of Fe/FeOx nanoparticles. These spherical 15 nanometer particles were studied for their potential application as MRI contrast agents. In addition, the aqueous ferrofluid served as a precursor for the design of magnetic/luminescent core/shell nanoparticles. Finally, the polyol method was extended to create Co/C nanoparticles for permanent magnet applications.
473

Synthesis, Characterization, and Functionalization of Magnetic Iron Nanoparticles for Enhanced Biological Applications

Warren, Christopher 10 December 2013 (has links)
The transition metal ferrites of composition MFe2O4 where M is Fe, Co, or Ni are well established materials for various biological applications due to their interesting magnetic properties. Their elemental and stochiometric composition can be easily manipulated which allows further tuning of their ferrimagnetic properties. By changing the identity of M and by changing the crystallite size of the ferrites, nanocrystals with diverse magnetic properties can be systematically produced. Furthermore, ferrites are more stable in diverse chemical environments, as compared to metallic nanoparticles, which make ferrites particularly useful for a broad range of biomedical applications, especially in the field of magnetic resonance imaging and cell labeling. In this work, spinel ferrites of composition CoFe2O4, NiFe2O4, and Ni.5Co.5 Fe2O4 were synthesized by a polyol method utilizing ethylene glycol as the solvent, reducing agent, and surfactant. The nanoparticles produced were surface coated with 3-aminopropyltriethoxy silane to increase solubility as well as to serve as an anchor for further conjugation with targeting substrates such as peptides and antibodies. The first part of this dissertation was focused on using the polyol method to produce nanoparticles of various metallic compositions. In each case, the polyol method provided an easy one-pot method to produce metallic as well as metal oxide nanocrystals. Utilizing the polyol method, ferrites of CoFe2O4, NiFe2O4, and Ni.5Co.5 Fe2O4 were produced with size ranges between 20 nm and 50 nm depending on the reaction time in the polyol. The second part of this dissertation was concerned with the functionalization of the nanoparticles to serve as an anchor for further conjugation with targeting substrates in the immunoaffinity separation of food borne pathogens. These nanoparticles were functionalized using an anti-E. coli O157:H7 antibody, mixed with a food matrix, and then subsequently removed from the food matrix by an external magnet in order to be analyzed by Matrix Assisted Laser Desorption Ionization/Time of Flight (MALDI/TOF) Mass Spectrometry as a rapid identification method of bacterial pathogens. Furthermore, magnetic resonance imaging (MRI) was carried out on the polyol produced ferrites in order to measure the transverse relaxation time (T2) of the nanoparticles in order to investigate the size dependence and crystallite composition of the particles ability to affect the transverse relaxivity rarte (r2). Further understanding of how ferrite composition and crystallite size affect their magnetic properties and resulting MRI contrast abilities will provide insight into the best materials for the next generation of contrast agents. Lastly, the ability of nanoparticles to serve as a stationary phase material for reversed phase ultrahigh pressure liquid chromatography will be discussed as a novel separation technique.
474

Graphene-Supported Metal Nanoparticles For Applications in Heterogeneous Catalysis

ELAZAB, HANY 01 January 2013 (has links)
Due to its unique properties and high surface area, Graphene has become a good candidate as an effective solid support for metal catalysts. The Nobel Prize in Physics for 2010 was awarded to Andre Geim and Konstantin Novoselov "for groundbreaking experiments regarding the two-dimensional material graphene". Microwave-assisted synthesis of various metallic nanostructured materials was investigated for CO oxidation applications. These metallic nanostructured materials were used to convert CO to CO2 as an effective approach for carbon monoxide elimination due to its harmful effect on health and environment. In particular, this dissertation is focusing on palladium as a transition metal that has a unique ability to activate various organic compounds to form new bonds. The prepared graphene-supported metallic nanostructured materials were successfully used to investigate Suzuki cross-coupling reaction as an important reaction in the field of pharmaceutical applications. In this research, nanostructured materials were used as solid support catalysts which showed remarkable improvements in the aspects of size, surface structure, catalytic selectivity, shape and recyclability. The nano porous structure and superparamagnetic behavior of (Fe3O4) nano particles that were used as an effective ingredient in graphene-supported palladium catalyst improved the catalytic activity and the catalyst recyclability simply by using an external magnetic field. This research has been divided into two main categories; the first category is to investigate other metal oxides as a solid support for palladium to be used in CO oxidation catalysis. The second category will focus on improving of solid support systems of palladium – magnetite catalyst to increase recyclability. The final stage of this investigation will study the use of these solid supported metal catalysts in continuous heterogeneous processes under flow reaction conditions. The structural, morphological and physical properties of graphene-based nanocomposites described herein were studied using standard characterization tools such as TEM, SEM, X-ray diffraction, XPS and Raman spectroscopy.
475

Nanomateriály na bázi oxidu titaničitého / Titania-based nanomaterials

Zabloudil, Adam January 2015 (has links)
Titanium dioxide colloid with a size of particles between 20 - 40 nm was prepared. Subsequently, three substances were syntetized - methylen bis(phosphonic) acid H4L1 , 4-phosphono-butyric acid H3L2 and 4-hydroxy-4,4-diphosphono-butyric acid H5L3 . Surface of the colloidal nanoparticles was modified using these substances (H4L1 , H3L2 and H5L3 ). Then stability of these systems was studied using acid-base titration and addition of calcium ions. Keywords: TiO2, nanoparticles, surface modification
476

Nanomaterials Self-Assembly Driven by Beta-Amyloid Peptides

Tanase, Maria Elena 20 May 2005 (has links)
Nanomaterials such as gold nanowires and gold nanoparticles were self-assembled with several peptides derived from betaamyloid peptide. The peptides propensity to form fibrilar structures was exploited. The products obtained by aggregation of the peptides with the nano materials were studied using HPLC, UV-vis spectroscopy, TEM and optical light microscopy.
477

Spectroelectrochemical graphene-silver/zinc oxide nanoparticulate phenotype biosensors for ethambutol and pyrazinamide

Tshoko, Siphokazi January 2019 (has links)
>Magister Scientiae - MSc / Tuberculosis (TB), a deadly disease second to HIV/AIDS, is a global health problem. Diagnosis of active tuberculosis is tedious and requires expensive procedures since there is no recognizable method for sole detection of active TB. Although this is a deadly disease, treatment drug toxicity is also an issue that also causes fatalities in diagnosed patients. Therefore, a rapid sensitive and specific diagnostic method is imperative for TB drug management. In this study spectroscopic and/or electrochemical biosensors were developed for the detection and quantification of TB treatment drugs. The biosensors were constructed with electroactive layers of graphene oxide coupled to silver nanoparticles and/or zinc oxide nanoparticles. These nanoparticles coupled with graphene oxide sheets were covalently attached onto the enzymes such as Cytochrome P450-2D6 to achieve the electrochemical detection of the TB treatment drugs and obtain the required electron transfer between the electrode surface and enzyme. The surface morphology of graphene oxide, nanoparticles as well as the green synthesized nanocomposites were achieved using High-Resolution Transmission Electron Microscopy (HRTEM), Atomic Force Microscopy (AFM), and High- Resolution Scanning Electron Microscopy (HRSEM) while the elemental analysis were obtained using Fourier Transform Infrared Spectroscopy (FTIR), Energy Dispersive X-Ray (EDX), Raman spectroscopy and X-Ray diffraction (XRD). Additionally, the optical properties of the developed nanocomposites where further characterised using Small Angle X-ray Scattering (SAXS), Photoluminescence Spectroscopy (PL) and Ultraviolet Spectroscopy (UV-vis). The electrochemical studies were obtained using cyclic voltammetry (CV) and showed an increase in electron conductivity for the green synthesized zinc oxide nanoparticles coupled with graphene oxide (ZnONPs/GO) and silver nanoparticles coupled with graphene oxide (AgNPs/GO) nanocomposite which was an indication that they were suitable as platforms towards biosensor development. Furthermore, amperometric technique was also used for biotransformation of the TB treatment drugs (Ethambutol and Pyrazinamide) in standard solutions of 0.1 M phosphate buffer (pH 7.0). Furthermore, the sensitivity value of 0.0748 μA/μM was determined for the ethambutol biosensor while a value of 0.1715 μA/μM was determined for the pyrazinamide biosensors. Very good detection limits were obtained for the standard solutions of ethambutol and pyrazinamide where a value of 0.02057 nM was determined for ethambutol at concentration linear range of 50 μM – 400 μM. Additionally, a value of 0.8975 x 10-2 nM was determined for pyrazinamide at the concentration linear range of 100 μM – 300 μM. The determined limit of detections have provided a clear indication that these biosensors have potential of being used in human samples since these values are below the peak serum concentrations of these drugs in TB diagnosed patients as reported in literature. This was further confirmed by the limit of quantification values determined for each biosensor where a value of 0.8975 x 10-2 nM was determined for pyrazinamide and a value of 0.02057 nM was determined for ethambutol.
478

Palladium-based Catalyst for Heterogeneous Photocatalysis

Elhage, Ayda 09 July 2019 (has links)
Over the past decade, heterogeneous photocatalysis have gained lots of interest and attention among the organic chemistry community due to its applicability as an alternative to its homogeneous counterpart. Heterogeneous catalysis offers the advantages of easy separation and reusability of the catalyst. Several studies showed that under optimized conditions, efficient and highly selective catalytic systems could be developed using supported metal/metal oxide nanoparticles. In this dissertation, we summarize the progress in the development of supported palladium nanoparticles for different types of organic reactions. Palladium-decorated TiO2 is a moisture, air-tolerant, and versatile catalyst. The direct excitation of Pd nanoparticles selectively isomerized the benzyl-substituted alkenes to phenyl-substituted alkenes (E-isomer) with complete conversion over Pd@TiO2 under H2-free conditions. Likewise, light excited Pd nanoparticles catalyzed Sonogashira coupling, a C-C coupling reaction between different aryl iodides and acetylenes under very mild conditions in short reaction times. On the other hand, UV irradiation of Pd@TiO2 in alcoholic solutions promotes alkenes hydrogenation at room temperature under Argon. Thus, The photocatalytic activity of Pd@TiO2 can be easily tuned by changing the irradiation wavelength. Nevertheless, some of these systems suffer from catalyst deactivation, one of the main challenges faced in heterogeneous catalysis that decreases the reusability potential of the materials. In order to overcome this problem, we developed an innovative method called “Catalytic Farming”. Our reactivation strategy is based on the crop rotation system used in agriculture. Thus, alternating different catalytic reactions using the same catalyst can reactivate the catalyst surface by restoring its oxidation states and extend the catalyst lifetime along with its selectivity and efficiency. In this work, the rotation strategy is illustrated by Sonogashira coupling –problem reaction that depletes the catalyst– and Ullmann homocoupling –plausible recovery reaction that restores the oxidation state of the catalyst (Pd@TiO2). The selection of the reactions in this approach is based on mechanistic studies that include the role of the solvent and evaluation of the palladium oxidation state after each reaction. In a more exploratory analysis, we successfully demonstrated that Pd nanoparticles could be supported in a wide range of materials, including inert ones such as nanodiamonds or glass fibers. The study of the action spectrum shows that direct excitation of the Pd nanoparticles is a requisite for Sonogashira coupling reactions. The main advantages of heterogeneous catalysis compared to its homogeneous counterpart are easy separation and reusability of the catalyst. Finally in order to facilitate catalyst separation from batch reaction and develop a suitable catalytic system for continuous flow chemistry, we employed glass fibers as catalyst support for a wide variety of thermal and photochemical organic reactions including C-C coupling, dehalogenation and cycloaddition. Different metal/metal oxide nanoparticles, namely Pd, Co, Cu, Au, and Ru were deposited on glass wool and fully characterized. As a proof of concept, Pd decorated glass fibers were employed in heterogeneous flow photocatalysis for Sonogashira coupling and reductive de-halogenation of aryl iodides.
479

NANOBOTS Smart Systems to Improve Therapeutics Delivery

alsaiari, shahad 10 1900 (has links)
With the remarkable advancement in the nanoparticles (NPs)-based drug delivery systems (DDS) over the past several decades, the pharmacological properties associated with conventional free drugs delivery are improved. In this thesis, we report potential candidates for the next-generation NP-based DDS. While natural DDS are promising as they possess exceptional delivery mechanisms and selective targeting, synthetic DDS are more favorable for their low immunogenicity. Our developed natural DDS called magnetotactic bacterial cages (MBC), which is based on magnetotactic bacteria (MTB) as a guidable delivery vehicle for DNA functionalized gold nanoparticles (AuNPs). Loading DNA functionalized AuNPs in MTB aided in increasing the maximum-tolerated dose of DNA functionalized AuNPs and tackled issues related to DNA functionalized AuNPs stability and systemic delivery. Natural DDS hold great advantages; however, it is difficult to make complete prediction about their immunogenicity and toxicity on the basis of preclinical trials. Thus, we assessed the efficacy of synthetic NP-based DDS. Using inorganic platforms, we were able to develop the first visual monitoring system of bacteria-NPs interaction. The system offers simultaneous sensing and inhibition of bacteria in infected cells. The system is comprised of Au nanoclusters @lysozyme (AuNC@lys) colloids MSN loaded with antibacterial agents. The applicability of the inorganic DDS in the biomedical field has been limited by the high bioaccumulation risks. Hybrid materials combine the advantages of organic, inorganic and natural carriers, offering opportunities for enhanced stability, manipulating release behavior and combine two or more functions in a single platform. To further enhance the properties our inorganic DDS, we incorporated light-responsive organic ligands to silicabased NPs. Plasmid DNA was loaded on the light-responsive bridged silsesquioxane nanocomposites (BS NPs). Light irradiation was performed to reverse the surface charge of NPs via a photoreaction of the organic fragments (silsesquioxane) within the NPs, that resulted in the release of plasmid DNA in HeLa cancer cells. Finally, we assessed a new class of organic-inorganic DDS composed of inorganic metal ions and organic linkers, zeolite imidazolate frameworks-8 (ZIF-8). These NPs showed exceptional ability to entrap large cargo due to their tunable porosity and structural flexibility.
480

Synthesis and characterization of bimetallic platinum nanoparticles for use in catalysis

Mathe, Ntombizodwa Ruth January 2015 (has links)
A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the Degree of Doctor of Philosophy. Johannesburg, 2015 / Bimetallic platinum nanoparticles were synthesized for application as anode catalysts for low temperature fuel cells such as direct methanol fuel cells (DMFCs). Two distinct synthesis procedures were used; namely conventional synthesis with post-synthesis heat treatment, and secondly polyol microwave-irradiation without further heat-treatment. The aim was to synthesize interesting and novel bimetallic nanostructures and relate their shape and morphologies to their methanol oxidation reaction (MOR) activities and their CO tolerance. Due to the high cost of the conventional synthesis processes as well as their use of harmful solvents, microwave-irradiation was explored as a possible synthesis procedure. It is a greener and more environmentally friendly approach with possibilities of mass production of the nanoparticles. For both the synthesis procedures, the reducing agent, the precursor salts, surfactants, pH of the solution and molar ratios were varied to determine the effect on the shape, size and ultimately the electrocatalytic activities of the Pt-Co and Pt-Ni nanoparticles. For the conventional synthesis procedure, the main parameter of comparison was the strength of the reducing agents, where NaBH4 and N2H4 were used under the same reaction conditions. In this study, the strength of the reducing agent affected the properties of the Pt-Co and Pt-Ni nanoparticles, such that, the stronger the reducing agent, the higher the degree of alloying and the more electrocatalytically active the materials. The drawback in the conventional synthesis was however low current outputs, in the microamps range, which necessitates a need to explore other synthesis procedures. Microwave-irradiation was thus used as an alternative synthesis procedure in an attempt to produce more active bimetallic platinum nanoparticles. Different reaction parameters were changed in this process to optimize the synthesis process, namely the pH of the solution, the amount of surfactant and the Pt-Ni molar ratio. In changing the reaction parameters, there was an observed change in the structure of the nanoparticles, with an average size in the order of 5 nm and different MOR activities. Furthermore, it was found that the activity was highest for the optimum amount of PVP and NaOH concentration of 500 mg and 1.0 M NaOH. In general, the MW synthesized nanoparticles achieved current values in the microamps to amps range, making it a more attractive synthesis procedure compared to the conventional method. The CO tolerance of the materials is an important aspect, as one of the main drawbacks of the commercial application of fuel cells is the propensity of Pt to get poisoned by CO during the methanol dissociation process. Therefore CO stripping measurements were performed on the MW-irradiated catalysts. The catalysts produced in this work showed good resistance towards CO. In general, the behaviours of the catalysts were dependent on the amount of surfactant and the molar ratio of the starting solution. The mechanism of CO tolerance in this case was determined as the bifunctional model, where the Ni-oxide and Ni-hydroxide species donate O to the electrooxidation of CO to CO2. In conclusion, the study of microwave-irradiated bimetallic nanoparticles performed here, resulted in highly active catalysts, which are even more active than commercial Pt/C nanoparticles.

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