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. / Surface 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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/19299 |
| Date | January 2016 |
| Creators | Mlambo, Mbuso |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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