Ultrasound-Assisted Green Synthesis of Ultra-Small Silver Nanoparticles and Their Antibacterial Activity

The green synthesis of silver nanoparticles (AgNPs) has garnered significant attention due to its eco-friendliness, safety, and time efficiency. This study explores the ultrasound-assisted synthesis of AgNPs using an aqueous extract of Hopea odorata (HO) and evaluates their antibacterial properties. The reaction conditions, silver ion concentration, ultrasound amplitude, and time, were optimized using UV-Vis spectroscopy, achieving nanoparticle synthesis in just 30 min. Comprehensive characterization revealed ultra-small HO-AgNPs with an average size of 2.8 nm, confirmed by SEM, TEM, FTIR, XRD, DLS, and zeta potential analyses. FTIR results suggested phenolic compounds in the extract act as stabilizing and reducing agents, while the highly negative zeta potential (–40.9 mV) indicated excellent stability. Antibacterial tests demonstrated strong activity against Staphylococcus aureus, Bacillus cereus, Escherichia coli, and Pseudomonas aeruginosa, with the highest efficacy against P. aeruginosa. These findings highlight HO-AgNPs as promising ultra-small nanoparticles with potent antimicrobial potential.