Extracts from the leaves of the African tree, the velvet bushwillow, Combretum molle, can be used as a bio template for the environmentally friendly synthesis of silver nanoparticles with antibacterial, antifungal, and antioxidant activity. Chemists Z. Nate, M.J. Moloto, P.K. Mubiayi, and F.M. Mtunzi of Vaal University of Technology, and N.P. Sibiya of the University of Kwazulu-Natal, and South Africa, explain details of their novel process this week in the International Journal of Nano and Biomaterials.
Plant extracts have been used successfully in the synthesis of metal nanoparticles. Indeed, aqueous extracts of Combretum molle have been used previously. The presence of tannins, proteins, flavonoids, and phenols allows the extracts to reduce metal salts in solution to insoluble metal particles while the same biomolecules can also act as capping agents that control the growth of those very nanoparticles and act to “cap” the surfaces.
In the present work, the team has successfully generated silver nanoparticles in a narrow range of sizes from 1 to 30 nanometres. They found that silver nanoparticles made in this way were more effective against a range of microbes than nanoparticles made using a standard non-biological procedure. Activity was demonstrated against important pathogenic species: Candida albicans, Cryptococcus neoformans, Staphylococcus aureus, Enterococcus faecalis, Klebsiella pneumonia, and Pseudomonas aeruginosa.
“These results indicated that the synthesised silver nanoparticles can be used as growth inhibitors against the studied bacteria and fungi species as they showed better inhibition than the already available antibacterial and antifungal agents,” the team writes. They add that the capped silver nanoparticles have antioxidant activity but it is not as great as the activity of the aqueous extract from the plant itself.
Nate, Z., Moloto, M.J., Sibiya, N.P., Mubiayi, P.K. and Mtunzi, F.M. (2019) ‘Green synthesis of silver nanoparticles using aqueous extract of Combretum molle leaves, their antibacterial, antifungal and antioxidant activity’, Int. J. Nano and Biomaterials, Vol. 8, Nos. 3/4, pp.189–203.