Bioengineering of gold nanoparticles using selected South African extracts

Abstract

The use of pharmaceutical products has played a big role in maintaining or improving the health of humans, and these benefits have driven pharmaceutical industries to be the most lucrative investments for many years including 2020. Lives have been saved, extended, and preserved through the use of medication since it was introduced. Although the use of medication has been known to provide relief to human health, the record of drug resistance, as well as the discovery of pharmaceutical drugs in municipal effluents was proof that pharmaceutical drugs need monitoring due to their impact on the ecosystem. A possible response to this concern lies in the exploration of potential sources of biologically active compounds from green nanotechnology. Noble metal nanoparticles, such as gold nanoparticles, have been identified as a potential alternative. The formation of gold nanoparticles was therefore achieved using Olea exasperata leave extract and isolated compounds as reducing agents. Three phytochemicals were isolated from Olea exasperata namely hydroxytyrosol, hydroxytyrosol glucoside, and oleuropein. Nuclear Magnetic Resonance and Infrared spectroscopy were used to confirm the structure of the isolated compounds. The formation of gold nanoparticles was confirmed using Ultraviolet-Visible (UV-VIS) spectroscopy by examining the surface plasmon resonance absorption between 530 and 560 nm. The synthesis of gold nanoparticles using oleuropein and hydroxytyrosol glucoside proved that all the selected reducing agents successfully reduced the gold ions to produce gold nanoparticles. The formed nanoparticles were fully characterised and showed a better Gaussian distribution than the nanoparticles obtained from the total extract. The stability of the gold nanoparticle solution was proven by a negative value of Zeta potential. X-Ray Diffraction (XRD) and Selected Area Electron Diffraction (SAED) analysis confirmed the crystallinity of the particles. The micrographs from High-Resolution Transmission Electron Microscopy (HRTEM) revealed the distinct shapes of the formed gold nanoparticles. The biological studies showed that both gold nanoparticles prepared by oleuropein and Olea exasperata extract have an affinity towards cancerous cells in comparison to normal cells. In summary, this work validated the necessity to form gold nanoparticles from pure reducing agents against the use of total fraction or fraction containing mixtures of compounds toward biomedical application.