3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Design and development of multifunctional Raman active noble metals nanoprobes for the detection of malaria and tuberculosis biomarkers(2016) Mlambo, MbusoSurface enhanced Raman spectroscopy (SERS) has emerged as a surface sensitive vibrational technique that leads to the enhancement of the Raman scattering molecules on or close to the surface of a plasmonic nanostructure. The enhancement is found to be in orders of 104 to 1015, which allows the technique to be sensitive enough to detect a single molecule. In this study, we report on the synthesis of different sizes of gold and silver nanoparticles (AuNPs and AgNPs) and gold nanorods (AuNRs). These are functionalized or co-stabilized with different stoichiometric ratios of HS-(CH2)11-PEG-COOH and alkanethiols (Raman reporters), i.e.; HS-(CH2)11-NHCO-coumarin(C), HS-(CH2)11-triphenylimidazole (TPI), HS- (CH2)11-indole (HSI), HS-(CH2)11-hydroquinone (HQ) to form mixed monolayer protected clusters (MMPCs). The alkanethiols were chosen as Raman reporters to facilitate the selfassembled formation of monolayers on the metal surface, thus resulting in stable MMPCs. The optical properties and stability of MMPCs were obtained using ultraviolet-visible (UVvis) spectrophometry and a zeta sizer. Size and shape of the as-synthesized nanoparticles were obtained using transmission electron microscopy (TEM). The tendency of thiolcapped nanoparticles to form self-assembled ordered superlattices was observed. Their Raman activities were evaluated using Raman spectroscopy, with the enhancement factor (EF) being calculated from the intensities of symmetric stretch vibrations of C-H observed in the region of about 2900 to 3000 cm-1 in all SERS spectra. In all four different alkanethiols (Raman reporters), smaller size metal nanoparticles (14 nm for AuNPs and 16 nm AgNPs) showed higher EF compared to 30 and 40 nm metal nanoparticles. The EF was observed to increase proportionally with stoichiometric ratios of alkanethiols from 1% iv | P a g e to 50%. The prepared MMPCs with small sizes were used as a SERS probe for the detection of malaria and tuberculosis biomarkers.Item Synthesis of DI- and trialkylthiourea complexes of Cd, Mn and Ni as precursors for phosphonoacetic acid (PAA)-capped metal sulphide nanoparticles(2010-08-03) Mlambo, MbusoMany studies on thiourea and its derivatives in different metal (II) complexes have confirmed that coordination is through the sulphur atom. The bonding of substituted thioureas to different metals was confirmed with a combination of spectroscopic studies such as IR and NMR spectroscopy and elemental analysis. A series of metal (II) di- and trialkylthioureas complexes have been synthesized and characterized. Their bonding through sulphur atoms rendered these complexes good precursors for the preparation of metal sulphide nanoparticles. Thermogravimetric analysis on the complexes was undertaken to check their suitability as precursors for the synthesis of nanoparticles and their potential as precursors for metal sulphide thin films using the chemical vapour deposition (CVD) technique and their general chemical and thermal stability. All the complexes reported in this work were used as single source molecular precursors for the synthesis of cadmium, manganese and nickel sulphide nanoparticles. In this study the investigation on the influence of capping agent and temperature on the size and morphology of nanoparticles was undertaken. Nanoparticles obtained by thermolysis of precursors in phosphonoacetic acid (PAA) were bigger in size and rod-shaped compared to smaller rods obtained in hexadecylamine (HDA). CdS nanoparticles prepared using PAA as a capping agent showed a huge blue-shift of the band edge from the bulk of 515 nm, compared to CdS nanoparticles obtained using HDA as a capping agent. When PAA was mixed with trioctylphosphine oxide (TOPO), a blue shift of band edges in all the bulk materials of different metal sulphides prepared was observed and the rod-shaped nanoparticles changed to spherical particles.