Green synthesis and antibacterial activity of silver and gold nanoparticles using crude flavonoids extracted from Bombax ceiba flowers

Bioeffects of AgNPs and AuNPs from Bombax ceiba

Abstract

The present study explores the simple and eco-friendly green synthesis of silver (AgNPs) and gold (AuNPs) nanoparticles using aqueous flower extract of Bombax ceiba, commonly known as silk cotton. The extract, rich in flavonoids, serves as both a reducing and capping agent, facilitating the synthesis of metal nanoparticles. The synthesized nanoparticles were characterized using UV spectroscopy and scanning electron microscopy (SEM), confirming their formation and stability. The antibacterial activity of the AgNPs, AuNPs, and crude flavonoids was evaluated against several bacterial strains, including Salmonella typhi, Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, and Staphylococcus aureus, using the agar well diffusion method. Our results show that AgNPs exhibit significant antibacterial activity, particularly against Gram-negative bacteria, with a marked zone of inhibition observed for S. typhi and E. coli. The inhibition zone increased with higher concentrations of AgNPs. In contrast, AuNPs and flavonoid solutions demonstrated only mild antibacterial effects, with no significant inhibition observed at lower concentrations (1–6 µL). The antibacterial efficacy of AgNPs was comparable to that of standard antibiotics, such as Azithromycin for Gram-positive bacteria and Ciprofloxacin for Gram-negative bacteria, suggesting their potential as effective antimicrobial agents. The antibacterial activity of the synthesized nanoparticles and the crude flavonoid extract highlights the promising use of Bombax ceiba flower extract in the green synthesis of metal nanoparticles with potential biomedical applications.