Masters Degrees (Physics)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/3639

Browse

Browsing Masters Degrees (Physics) by Subject "Amino acids"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Surface enhanced Raman spectroscopy (SERS) of amino acids
    (Stellenbosch : Stellenbosch University, 2016-03) Pfukwa, Ngaatendwe Buhle Cathrine; Neethling, Pieter H.; Rohwer, Erich G.; Schwoerer, Heinrich; Stellenbosch University. Faculty of Science. Dept. of Physics
    ENGLISH ABSTRACT : Raman spectroscopy (RS) is an invaluable technique for sample identification. This method requires little sample preparation and is not completely non-invasive. The intensity of Raman scattered light can be enormously increased or boosted when a sample molecule is adsorbed on a metallic surface, a technique known as Surface Enhanced Raman spectroscopy (SERS). Since the development of this technique a lot of studies have been done on molecules adsorbed on various types of metallic structures due to the sole purpose of the increase in Raman signal which occurs under such conditions. This has led to the applications of SERS in industry and in basic research. In this study, silver and gold nanospheres of average size 20 nm were successfully synthesised and characterised using UV-Vis (Ultraviolet-visible) spectroscopy and Transmission Electron Microscopy (TEM). Two RS setups were available, a double stage Raman spectrometer using 514.5 nm Ar+ laser as excitation source and a single stage Raman spectrometer using 532 nm frequency doubled Nd:YAG laser as excitation source. The synthesised silver nanospheres were employed in SERS studies on biomolecules (amino acids) using the single stage Raman setup with the aim of advancing SERS as a bio-analytical tool using our in-house developed RS setup. Qualitative analysis was done on amino acid spectra by band profiling and quantitative analysis was performed by carrying out concentration studies so as to determine the detection limit of the measuring instrument. Results are explained based on the setup used and by comparing with what is expected from literature. It was found that amino acids mostly adsorb on a metallic surface via the common carboxylate, amine and R-groups. This is due to the availability of free electron pairs on the oxygen and nitrogen atoms which take part in charge transfer mechanisms and promote chemical enhancement. It was also observed that some amino acids have functional groups which either have strong affinity for metals or have an electronic structure that contribute to chemical enhancement, thus boosting the Raman signal. A low detection limit of 1x10-4 M from amino acid L-Lysine was obtained. Ultimately, these results are new and provide a set of measurements done on four groups of amino acids using gold and two types of silver nanoparticles. These results form a foundation for future studies on larger biological organisations using the setup available in our labs.