Synthesis, characterization and functional evaluation of gold nanoparticles prepared using Dovyalis abyssinica leaf extracts as reducing and surface capping agent

Abstract

Green synthesis of nanoparticles using plants and microorganisms is biologically safe, cost effective, and environmentally friendly technology. Gold nanoparticles (Au NPs) were synthesized using aqueous extracts of leaves of Dovyalis abyssinica as reducing and surface capping agent and the catalytic activity, antibacterial action and antioxidant potential of the synthesized AU NPs were evaluated. Firstly, HAuCl₄ was synthesized in the laboratory from metallic gold and hydrochloric acid using a predesigned method. Secondly, Au NPs was synthesized by mixing HAuCl₄ and the plant extract at 45 ^oC with a digestion time of 1 h. The size of the nanoparticles was modulated by varying the ratio of the plant extract and HAuCl₄ with known concentrations. The synthesized Au NPs showed strong absorption around 540 nm which lies in the characteristic absorption region of Au metal nanoparticles (520–580 nm). The X-ray diffraction spectrum of the synthesized Au NPs showed characteristic crystalline structures of gold. The scanning electron spectroscopy images of the synthesized Au NPS revealed the presence of mixed shapes predominantly of irregular shapes and a particle size analyzer displayed an average size of 63.13 nm. The fourier-transform infrared spectrum of Au NPS confirmed the presence of amine, carbonyl and hydroxyl functional groups as surface capping molecules. Although the synthesized Au NPs showed poor bacterial growth inhibition activity on two selected bacteria, it demonstrated excellent free radical scavenging activity against 2, 2-Diphenyl-2-picrylhydrazyl (DPPH) radical and good catalytic activity for degrading bromothymol blue and methyl red compounds. In contrast to the hexane and ethyl acetate extracts, the aqueous fraction was identified as powerful reducing fraction for the synthesis of Au NPs in this experiment.