Abstract
M.Sc.(Nanoscience)
The synthesis and application of gold nanoparticles (AuNPs) has been intensively studied
worldwide. However, the toxicity of these nanoparticles is still a concern. We considered that various physiochemical methods used to synthesize AuNPs are energy driven, costly and require the use of harmful chemicals. Thus, this makes them not environmentally-friendly. The aim of this study was therefore to synthesize AuNPs via a greener route using Aspalathus linearis tea leaves. The AuNPs were used to coat eight commercial antifungal discs (i.e. amphotericin B, fluconazole, clotrimazole, econazole, flucytosine, ketoconazole, miconazole and nystatin) against four Aspergillus spp. for enhanced antifungal activity. The aqueous extract of A. linearis was characterized by high performance liquid chromatography and liquid chromatography–mass spectroscopy. The AuNPs were characterized using ultravioletvisible (UV-vis) spectroscopy, dynamic light scattering, nanoparticle tracking analysis, Fourier transforms infrared spectroscopy (FTIR), high-resolution transmission electron microscopy and X-ray diffraction. The toxicity of the synthesized AuNPs was studied by 3-(4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay and xCELLigence test on HepG-2 cell lines and results revealed very little to no toxicity of the AuNPs. The pristine antifungal and AuNPs coated antifungal discs were characterized by FTIR, scanning electron microscopy (SEM) and antifungal activity performed using the disc diffusion method. A strong resonance peak was observed at 529 nm of the AuNPs measured using UV-vis spectroscopy. Average size of AuNPs was ~44±1 nm and demonstrated excellent in-vitro stability under various solutions (5% NaCl, phosphate
buffered saline) at varying pH levels. The SEM images revealed that the AuNPs were
attached onto the coated antifungal discs when compared with the pristine antifungal discs. Antifungal results indicated that AuNPs significantly (p<0.001) enhanced the antifungal activity of the coated antifungal discs against the tested fungi when compared to the pristine antifungal discs. The AuNPs coated econazole disc exhibited the greatest (broad spectrum) activity than other antifungal agents tested. In conclusion, A. linearis can be used as a reducing agent in the synthesis of stable AuNPs. Furthermore, the AuNPs coated antifungal discs demonstrated considerable antifungal activity over the pristine antifungal discs...