Green synthesis of silver nanoparticles and their antibacterial activities

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 , , and 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 , , and , respectively; those starch-mediated showed inhibition of 7, 13, and 12 mm, respectively. AgNPs’ minimum inhibitory concentrations were 6.25 μg·mL toward both and and 12.5 μg·mL against when using starch in biosynthesis, whereas they were 19.6 μg·mL against both and and 9.81 μg·mL toward when using biomass. Synthesized AgNPs have promising antibacterial potential.