Synthesis temperature and time affect size, distribution and bioactivity of Tetradenia riparia-produced AgNPs

Abstract

Leaf extracts of Tetradenia riparia were used to synthesise silver nanoparticles (AgNPs) using 1 mM silver nitrate for 6, 12 and 24 h at room temperature (RT) and at 80 °C. There were no significant differences in nanoparticle (NP) yield between synthesis at RT and at 80 °C, and amongst the different synthesis times (6, 12 and 24 h) (p>0.05). Fourier transformed infrared spectroscopy analyses confirmed the presence of functional groups. The AgNPs were mostly spherical in shape. The largest AgNPs were observed following 12 h synthesis at RT with an average diameter of 32.2±12.4 nm. Smaller AgNPs (17.5±10.7 nm) were recorded following synthesis for 24 h at 80 °C. The growth of Methicillin-resistant Staphylococcus aureus (MRSA) was inhibited by AgNPs synthesized for 24 h at RT, as well as by those synthesized for 12 h and 24 h at 80 °C with a concentration of 125 μg.ml −1 each, compared to Neomycin, where inhibition was recorded at 250 μg.ml −1 . A similar finding was observed for Escherichia coli where the minimum inhibitory concentrations (MICs) of the AgNPs synthesized for 12 h at RT and for 6, 12 and 24 h at 80 °C, were recorded at 125 μg.ml −1 each, compared to Vancomycin where it was 250 μg.ml −1 . Nanoparticles synthesized at 80 °C had a significantly lower MIC than Neomycin against MRSA (p=0.007), and a significantly lower MIC than Vancomycin against E. coli (p=0.01). It is indicated that anti-bacterial activity may be attributed to the size of NPs.

In situ facile green synthesis of Ag–ZnO nanocomposites using Tetradenia riperia leaf extract and its antimicrobial efficacy on water disinfection

“…The spatial distribution of Tetradenia riperia has been documented in various areas of African countries such as Rwanda 53 , Madagascar 54 , South Africa 55 , Uganda 56 and Tanzania 57 in which its medicinal potential has been attributed to abundant phytocompounds with antimicrobial effects 51 . Literature has reported the use of Tetradenia riperia leaves in the synthesis of various nanoparticles such as silver 58 , 59 . To the best of our knowledge, no study has reported on the synthesis of Ag–ZnO nanocomposites by using the aqueous leaves extract of Tetradenia riperia .…”

In situ facile green synthesis of Ag-ZnO nanocomposites using Tetradenia riperia leaf extract and its antimicrobial efficacy on water disinfection

“…The spatial distribution of Tetradenia riperia has been documented in various areas of African countries such as Rwanda [45], Madagascar [46], South Africa [47], Uganda [48] and Tanzania [49] in which its medicinal potential has been attributed to abundant phytocompounds with antimicrobial effects [43]. Literature has reported the use of Tetradenia riperia leaves in the synthesis of various nanoparticles such as silver [50,51]. To the best of our knowledge, no study has reported on the synthesis of Ag-ZnO nanocomposites by using the aqueous leaf extract of Tetradenia riperia.…”