Abstract

Synthesis of nanoparticles was done by green method. Aqueous extracts of Vernonia amygdalina, Telferia occidentalis and Lasianthera africana were used as the model vegetables. Silver nitrate was used as the silver precursor, while the plant extracts served as the reducing agents and Xanthan gum (0.25, 0.5, 0.75 and 1.00% w/v) was introduced as stabilizing agents. Twelve batches of silver nanoparticles were synthesized: 0.25% V. amygdalina, 0.50% V. amygdalina, 0.75% V. amygdalina, 1.00% V. amygdalina, 0.25% T. occidentalis, 0.5% T. occidentalis, 0.75% T. occidentalis, 1.00% T. occidentalis, 0.25% L. africana, 0.50% L. africana, 0.75% L. africana, and 1.00% L. africana. The nanoparticle formation was confirmed with the visible colour change from colourless to characteristic reddish brown and the plasmon resonance peak ranges from 350 to 500 nm. The surface plasmon resonance (SPR) characteristic peak for synthesized nanoparticles gave values from 371 to 452 nm. Nanoparticles synthesized from V. amygdalina and T. occidentalis had similar (p > 0.05) peaks for the surface plasmon resonance. Nanoparticles synthesized from L. africana had the least SPR (371 nm). After 9 months of storage, SPR and colour of nanoparticles remain unchanged. The antimicrobial activities of these nanoparticles were studied against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus subtilis. They had satisfactory inhibitions against the four test microorganisms. Among the different vegetables used in the study, L. africana had the highest sensitivity.

Key words: Silver nanoparticles, green method, characterisation, antimicrobial.