Comparative analysis of biosynthesised and chemosynthesised silver nanoparticles with special reference to their antibacterial activity against pathogens

The present study reports the synthesis of silver nanoparticles (AgNPs) using both biological and chemical routes to find out the best method for control of their size and activity. The fungal agent (Fusarium oxysporum) and the plant (Azadirachta indica) were found to be the best source for AgNPs synthesis. Both biosynthesis and chemosynthesis were achieved by challenging filtrate with AgNO₃ (1 mM) solution. The synthesised nanoparticles were characterised by ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, nanoparticle tracking analysis (LM20), zeta potential measurement and transmission electron microscopy. The biologically synthesised nanoparticles were spherical, polydispersed and in the range of 10-40 nm, while chemically synthesised nanoparticles were highly monodispersed with a size of 5 nm. The antimicrobial assay against Escherichia coli and Staphylococcus aureus proved biogenic AgNPs to be more potent antibacterial agents than chemically synthesised AgNPs. The possible antibacterial mechanism of AgNPs has also been discussed. Biogenic AgNPs have shown more activity because of the protein capping and their mode of entry into the bacterial cell. These findings may encourage the use of biosynthesis over the chemosynthesis method.