A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of a Master of Science degree in Chemistry. University of the Witwatersrand, May 2013 / The pollution of water sources by chemical and biological species has created a serious water crisis all over the world. Such pollution has placed severe strains on the limited water sources resulting in the spread of waterborne diseases, which continue to be the leading causes of deaths in developing countries. Pollution by organic species still poses a serious health and environmental problem. Attempts to mitigate this problem are on-going and a number of methods are employed currently. Activated carbon and reverse osmosis are some of the current techniques that are used for the removal of organics in water. However, these techniques are limited in the removal of pollutants at lower concentrations (ng/L). Recent studies demonstrated the efficient removal of organics by nanoporous cyclodextrin (CD) polymers, a class of nanomaterials with great potential in absorbing organic pollutants from water. This project reports on the synthesis of β-cyclodextrin (β-CD) based polymer nanocomposite materials (nanocomposites) that have been blended with nitrogen-doped carbon nanotubes (N-CNTs) and silver (Ag) nanoparticles for water treatment. Prior to this study, the synthesis of these nanocomposites has been based on a conventional method that involves heating the reactants in a round bottom flask for 16 – 24 h. In this study a new method that is efficient, greener and time saving is reported. This facile method involved synthesizing the polymer nanocomposites under microwave irradiation wherein complete synthesis of the polymer nanocomposites was achieved in 10 min. N-CNTs were first synthesized via modified chemical vapour deposition method (CVD) using a 10wt% Fe-Co/CaCO3 catalyst. The N-CNTs were found to contain ~ 2% nitrogen by CN and XPS analysis. The N-CNTs were of high purity and were oxidized with acid functional groups (-COOH, -C=O, -OH) using nitric acid under reflux. Zeta potential studies indicated that the quantity of acid functional groups increased with increase in acid treatment time. The functionalised N-CNTs (fN-CNTs) were then decorated with Ag nanoparticles using microwave irradiation and further polymerized with β-CD using hexamethylene diisocyanate (HMDI) as the linker in an industrial microwave under an inert gas atmosphere of N2. Two types of polymer nanocomposites were synthesized namely, N-CNTs/β-CD and Ag/N-CNTs/β-CD. Different synthesis parameters such as microwave power and time were varied during the synthesis of these composites to study their effect on the result materials. Different level of power, 400 W, 600 W and 800 W were tested and surface area and morphology data indicated that all these powers can be used in synthesising the polymer composites. The optimum power used was 600 W, which gave highly porous, less densely packed morphology and a higher surface area of the polymers. The synthesis time was varied for 10 min, 15 min and 30 min. An irradiation time of 10 min was found to be sufficient for the synthesis of the nanocomposites. The polymers showed an efficient removal of p-nitrophenol, bisphenol A and trichloroethylene (TCE) from spiked water as confirmed by UV-Vis spectroscopy and GC/MS analysis.

The mechanism of organothiol (OT) binding to gold has remained controversial for decades. There are three mechanisms proposed for OT binding to gold surfaces. The first is the radical pathway in which the sulfur-bound hydrogen atoms (RS-H) are released as hydrogen atoms which eventually converted into hydrogen gas. Second is the deprotonation pathway in which the sulfur-bound hydrogen atoms leave as protons. Third is direct adsorption in which the RS-H bonds remain intact on the gold surface. This study demonstrates a combined pH and surface enhanced Raman spectroscopic study of organothiol binding to citrate- and borohydride-reduced gold nanoparticles (AuNPs) in polar (water), moderately polar (dichloromethane), and nonpolar (toluene,hexane) solvents. Thiol deprotonation provides a unified pathway for OT binding to AuNPs regardless of solvent polarity of the ligand binding solutions. This work should contribute to resolve the long-standing debate on the fate of the sulfur-bound hydrogen of organothiols self-assembled on gold.

Semen contain a heterogeneous population of viable and non-viable (damaged) spermatozoa. Proportions of non-viable spermatozoa interfere with male fertility, with available techniques unable to selectively remove prior to breeding. Nanobiotechnology may allow removal, enriching semen with high quality spermatozoa for improved productivity. Here, we applied double nanopurification with boar semen using functionalized magnetic nanoparticles. Non-viable and viable spermatozoa were magnetically separated and verified through various microscopy imaging. Viable (nanopurified) spermatozoa showed no additional damages. Nanopurification did not interfere with sperm motility and viability, with beneficial effects on motion parameters. Nanopurified spermatozoa maintained fertility following insemination, with resulting offspring indicating no impaired growth or health performance. Pork quality was unaffected showing comparable characteristics to the control. In summary, the use of magnetic nanopurification in boar spermatozoa showed sperm viability and fertility improvements with successful offspring performance. This study shows promise for large-scale commercial applications to enhance male fertility and offspring performance.

Proteins and organothiols are known for their high binding affinity to noble metal surface including gold nanoparticles (AuNPs). Numerous reports have been dedicated to AuNP interaction with protein or organothiol alone. Competitive protein and organothiol (OT) interaction is, however, mostly an unexplored area. The research reported here focused on developing a fundamental understanding of sequential and simultaneous protein and organothiol interaction with AuNPs in which protein and OT are added either simultaneously or sequentially into the colloidal AuNP solutions. In studies of OT interactions with bovine serum albumin (BSA) stabilized AuNPs, we found that the protein coating layer is highly porous and permeable for small molecules such as mercaptobenzimidazole (MBI), cysteine (Cys), homocysteine (Hcy), and glutathione (GSH). Based on the amounts of MBI adsorbed and the kinetics of MBI adsorption onto BSA stabilized AuNPs, we were able to get an insight into protein conformational changes on the AuNPs. The competitive and sequential studies of protein and OT interactions with AuNPs involving eight model organothiols showed that the protein and OT cosorption onto AuNPs is a kinetically controlled process. The AuNP stability against ligandsorption-induced AuNP aggregation differed significantly among the AuNP/OT and AuNP/BSA/OT mixtures where the AuNP stability order increased from (AuNP/OT)/BSA to AuNP/(BSA/OT), and finally (AuNP/BSA)/OT samples (the two components inside the parenthesis are mixed first followed by the addition of the third component). The studies on the role of cysteine in protein-AuNP interactions found that the cysteine has no significant effect on the kinetics of protein adsorption onto AuNPs. However the stability of the protein-AuNP complex against the organothiolsorption induced AuNP aggregation increased as the number of cysteine residues increased from zero to two. Besides providing new insights on protein interaction with AuNPs, this research is important for AuNP biological/biomedical applications because AuNPs in biofuids encounter a mixture of proteins and OTs in addition to other molecular species.

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This thesis focuses on the optimization of surface enhanced Raman for bacteria detection. Many factors influence the outgoing Raman signal in SERS. Coating the nanoparticles used in SERS with a capping agent is one way to enhance the Raman signal. Capping agents can play a significant role in the interaction between the nanoparticles and the bacteria, in turn contributing to the detection of pathogens. To understand the potential of optimizing the capping agent for gold nanoparticles in SERS detection of bacteria, three capping agents — thioglucose (which was not applied previously for the SERS analysis of bacteria), polyvinylpyrrolidone (PVP), and citrate — were tested for their ability to improve species identification and Staphylococcus aureus strain discrimination. The generated samples were run under a dark-field microscopy integrated SERS setup. Upon discriminant analysis, the collected dataset showed that thioglucose and citrate performed well in species identification. However, thioglucose performed better than citrate and PVP in strain discrimination because of its strong ability to integrate with nucleic acid components inside the bacteria cells. The second experiment explored if SERS can be used to diagnose periprosthetic joint infections (PJI) in shoulder tissue sample. Since the application of SERS on tissue for diagnostic purposes is novel, both ex-situ and in-situ gold nanoparticles were tested. For the in-situ gold nanoparticle integration into tissue samples, the UV reduction method was applied on the samples to generate gold nanoparticles inside the tissues. Multiple conditions were applied on the tissue samples controlling the UV power and UV exposure time. The samples were run in the same dark-field integrated Raman setup initially. The collected data showed that the in-situ gold nanoparticle integration into the shoulder tissue samples through the UV reduction method was successful and has potential. However, the optimum SERS condition could not be confirmed from this analysis due to the high variation of the Raman signal from one tissue sample to the other which generated inconsistent results even in the same applied condition. This suggested that distribution of gold nanoparticle integrated to the tissue was uneven, and thus affected the consistency of the outcomes from the process. Dark field SERS setup was then modified, and a scanning microscope part was incorporated to the system. Rigorous analysis of the SERS spectra from the scanned image and the Raman band assignment of these spectra showed that region high in collagen and protein can provide strong SERS signal. Therefore, to decide on the optimum SERS condition for PJI diagnosis by SERS, scanned image spectra from samples should be obtained. The comparison of all averaged spectra calculated from the highest Raman integral spectra acquired for each condition can point out to the optimum SERS condition. Besides, the relevant band assignment of each spectrum can provide information to understand the mechanism of SERS on shoulder tissue samples.

Colloidal Microcapsules (MCs), i.e. capsules stabilized by nano-/microparticle shells are highly modular inherently multi-scale constructs with applications in many areas of material and biological sciences e.g. drug delivery, encapsulation and microreactors. These MCs are fabricated by stabilizing emulsions via self-assembly of colloidal micro/nanoparticles at liquid-liquid interface. In these systems, colloidal particles serve as modular building blocks, allowing incorporation of the particle properties into the functional capabilities of the MCs. As an example, nanoparticles (NPs) can serve as appropriate antennae to induce response by external triggers (e.g. magnetic fields or laser) for controlled release of encapsulated materials. Additionally, the dynamic nature of the colloidal assembly at liquid-liquid interfaces result defects free organized nanostructures with unique electronic, magnetic and optical properties which can be tuned by their dimension and cooperative interactions. The physical properties of colloidal microcapsules such as permeability, mechanical strength, and biocompatibility can be precisely controlled through the proper choice of colloids and preparation conditions for their This thesis illustrates the fabrication of stable and robust MCs through via chemical crosslinking of the surface engineered NPs at oil-water interface. The chemical crosslinking assists NPs to form a stable 2-D network structure at the emulsion interface, imparting robustness to the emulsions. In brief, we developed the strategies for altering the nature of chemical interaction between NPs at the emulsion interface and investigated their role during the self-assembly process. Recently, we have fabricated stable colloidal microcapsule (MCs) using covalent, dative as well as non-covalent interactions and demonstrated their potential applications including encapsulation, size selective release, functional devices and biocatalysts.

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