Characterization and Evaluation of Antibacterial Activity of Silver Nanoparticles Prepared from Sclerocarya birrea Stem Bark and Leaf Extracts

The synthesis of silver nanoparticles by using the stem extract and leaf extract of Sclerocarya birrea (Marula) and silver nitrate (AgNO₃) is reported. The synthesized nanoparticles were characterized using ultraviolet-visible spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, dynamic light scattering, and visual inspection. The antibacterial activity of the synthesized nanoparticles was done by agar disc diffusion method and tested against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). The ultraviolet visible absorption spectrum showed broad absorption band at around 430 nm corresponding to that of surface plasmon resonance of silver nanoparticles. The synthesis of silver nanoparticles was also confirmed by color change of AgNO₃ to reddish brown upon addition of Sclerocarya birrea stem and leaf extracts. In addition, change in color of the solution from colorless to brown within 5 min at pH 11 showed that the rate of reduction was faster at this pH compared to lower pH. Transmission electron microscopy analysis proved that the synthesized nanoparticles were spherical in shape; energy-dispersive spectroscopy analysis confirmed the presence of silver in the synthesized nanoparticles; and dynamic light scattering confirmed that the stem nanoparticles were generally larger (36 to 58 nm) than those synthesized from leaf extracts (32 to 48 nm).  These nanoparticles were found to possess potential antibacterial activity against E. coli and S. aureus.