Green synthesis of silver nanoparticles and their antibacterial activities

Abstract

Nanotechnology offers a solution to bacterial antibiotic resistance, which poses a serious threat to global health. Green synthesis of metallic nanoparticles is gaining increasing attention due to its environmental benefits. This study aimed to biosynthesize silver nanoparticles (AgNPs) by microwave irradiation through silver nitrate reduction using starch and microalgae biomass; characterize them using UV–visible spectroscopy, scanning electron microscopy-energy-dispersive X-ray microanalysis, and X-ray diffraction; and evaluate their antibacterial activity against Escherichia coli, Bacillus clausii, and Staphylococcus aureus using disk diffusion and broth dilution methods. Synthesized AgNPs showed a single peak related to surface plasmon resonance at 430 nm. Size range of spherical AgNPs was 40–150 or 90–400 nm for starch- or biomass-mediated NPs, respectively. Biomass-mediated AgNPs exhibited antibacterial activity with the inhibition zones of 8, 12, and 10.5 mm against E. coli, B. clausii, and S. aureus, respectively; those starch-mediated showed inhibition of 7, 13, and 12 mm, respectively. AgNPs’ minimum inhibitory concentrations were 6.25 μg·mL−1 toward both E. coli and S. aureus and 12.5 μg·mL−1 against B. clausii when using starch in biosynthesis, whereas they were 19.6 μg·mL−1 against both E. coli and S. aureus and 9.81 μg·mL−1 toward B. clausii when using biomass. Synthesized AgNPs have promising antibacterial potential.

Keywords

• green synthesis
• microwave
• silver nanoparticles
• microalgae
• antibacterial activity