Green-mediated gold nanoparticles from Allium c epa: Synthesis, characterization and antimicrobial properties

Green synthesis of metal nanoparticles has gained significant interest in biomedicine due to its cost-effectiveness and environmental compatibility. In this study, aqueous extracts of Allium cepa bulb and peel were employed as biogenic reducing, capping, and stabilizing agents for the synthesis of gold nanoparticles (AuNPs). The synthesized nanoparticles were tested against pathogenic bacteria. UV-Vis spectroscopy confirmed nanoparticle formation with distinct surface plasmon resonance peaks at 551 nm for bulb-derived AuNPs (OBNPs) and 539 nm for peel-derived AuNPs (OPNPs). FT-IR analysis indicated potential involvement of flavonoids, phenolic constituents, and sulphur-containing compounds in the reduction and stabilization processes, while X-ray diffraction (XRD) revealed characteristic face-centered cubic crystalline structures. SEM and TEM micrographs further showed extract-dependent morphological variations: OBNPs appeared irregular, polydisperse, and agglomerated, whereas OPNPs exhibited well-defined anisotropic features such as nanoplates and truncated plate-like structures. The broad particle size distribution (5-200 nm) reflects the influence of phytochemical composition on nucleation and growth. Energy-dispersive X-ray spectroscopy (EDX) confirmed the elemental presence of gold (>94%) in the nanoparticles. Both OBNPs and OPNPs exhibited strong antibacterial effects, with MIC and MBC values ranged from 0.625 to 1.25 and 5-10 mg/mL, respectively. Completed bacteria elimination was archived within 12-24 h. Overall, this work establishes Allium cepa, particularly onion peel waste, as a valuable, low-cost, and sustainable resource for stable AuNPs synthesis with potential for biomedical and antimicrobial applications.