Green synthesis of gold nanoparticles using Syrian propolis: optimization, characterization, and antibacterial applications

Abstract Green synthesis of gold nanoparticles (SP-AuNPs) was achieved using an aqueous Syrian propolis (SP) extract from Apis mellifera syriaca , acting as both reducing and stabilizing agent. HPLC analysis of the SP extract confirmed the presence of major phytochemical constituents including quercetin, kaempferol, caffeic acid, chrysin, apigenin, and cinnamic acid. The unique phytochemical composition of this local bioresource contributes to the novelty of the study and influences nanoparticle formation. SP-AuNP formation was confirmed using UV–Visible spectroscopy, where a characteristic surface plasmon resonance peak was observed at 541 nm. Dynamic light scattering analysis revealed a hydrodynamic size ( Z -average) of 82.01 nm with a polydispersity index of 0.202, indicating a narrow and homogeneous size distribution. The zeta potential value (−22.6 mV), suggested good colloidal stability. Morphological characterization using Field Emission Scanning Electron Microscopy and Atomic Force Microscopy demonstrated predominantly spherical nanoparticles with uniform distribution, particle sizes below 50 nm, and no significant aggregation. The antibacterial activity of SP-AuNPs was evaluated using the agar well diffusion method against S. aureus, S. epidermidis , and E.coli the results showed inhibition zones of 16 mm, 15 mm, and 18 mm respectively, while the minimum inhibitory concentration was 50 µ g ml ⁻¹ for both strains, and 40 µ g ml ⁻¹ for E.coli. These findings indicate that the SP-AuNPs possess stable physicochemical properties and promising antibacterial activity, supporting their potential use in biomedical applications.