Green synthesis of silver nanoparticles under ambient conditions using onion, turmeric, and galangal extracts with antibacterial activity against E. coli and S. aureus

This study developed a sustainable method for synthesizing antibacterial silver nanoparticles (AgNPs) using aqueous extracts of onion, galangal, and turmeric as natural reducing and stabilizing agents under ambient conditions. The extracts showed antioxidant activity (32.52–59.89%) and total phenolic contents of 2.26–4.03 mg GAE/g DW, enabling AgNP formation without hazardous chemicals or heating. UV–Vis spectra confirmed nanoparticle synthesis with surface plasmon resonance peaks at 406–425 nm. TEM analysis showed predominantly spherical particles of 8.71–13.73 nm, while zeta potentials (−28.02 to −31.65 mV) indicated good colloidal stability and XRD confirmed crystalline face-centered cubic silver. The AgNPs exhibited strong antibacterial activity against Escherichia coli ( E. coli ) and Staphylococcus aureus ( S. aureus ). All samples showed MIC / MBC of 50 µg/mL against S. aureus , whereas onion-derived AgNPs were most effective against E. coli ( MIC 200; MBC 400 µg/mL). These plant extracts are promising low-cost bioresources for green nanomaterial production.