Green synthesis of silver nanoparticles and their applications as an alternative antibacterial and antioxidant agents

Antimicrobial resistance is a complex global health challenge today. Discovery and development of new natural alternates with novel targets is utmost priority. In this experiment, alternative antibiotic agents in the form of silver nanoparticles (SNPs) and Achillea millefolium L. extracts were evaluated for antibacterial and antioxidant activity. The SNPs were synthesized using aqueous, ethanol and methanol extracts of A. millefolium and were monitored by a color change and UV-vis spectroscopy. The size and shape of the nanoparticles were determined through scanning electron microscopy and phase was assessed through X-ray diffraction. The SNPs were shown to have an average diameter of 20.77, 18.53 and 14.27 nm with spherical, rectangular and cubical shapes, synthesized from aqueous, ethanol and methanol extract respectively. The response of biomolecules present in plant extract during the formation of SNPs was analyzed by Fourier transform infrared spectrometry, showing polyphenols, proteins, carboxylic acid and alcohol are involved in the formation of SNPs. The plant extracts and SNPs were then studied for their antibacterial potential against common human pathogens such as gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis) and gram-negative bacteria (Salmonella enterica, Escherichia coli, and Pseudomonas aeruginosa), displaying a very good activity against both types of bacteria. The Methanol-SNPs exhibit greater inhibition of DPPH radicals with IC₅₀ 7.03 ± 0.31 μg/mL. This green method of synthesis of SNPs would support the production of SNPs with considerably boosted antibacterial and antioxidant properties and significantly enhanced therapeutic performance.