Green synthesis and molecular-level mechanism of silver nanoparticles from Pandanus fascicularis (Keya) leaf extract with antibacterial activity

With the global rise in multidrug-resistant bacteria, there is a critical need for sustainable antimicrobial agents. Silver nanoparticles (AgNPs) synthesized via plant extracts offer an eco-friendly and efficient approach, yet many phytochemical-rich plant sources remain underexplored. This study reports, for the first time, the green synthesis of AgNPs using Pandanus fascicularis (Keya) leaf extract—an indigenous coastal plant abundant in bioactive compounds. The synthesized AgNPs were characterized by UV-Vis spectroscopy, laser diffraction particle size analysis, and transmission electron microscopy (TEM), confirming their nanoscale size (20–25 nm), spherical morphology, and good colloidal stability. The AgNPs exhibited strong antibacterial activity against Staphylococcus aureus and Escherichia coli , with inhibition zones of 15 mm and 12 mm, respectively. To elucidate the molecular mechanism of nanoparticle formation, density functional theory (DFT) calculations were performed on representative phytochemicals (gallic acid and D -glucose) interacting with Ag⁺. The computational results confirmed spontaneous complex formation via oxygen donor atoms, supported by vibrational shifts, frontier orbital interactions, and binding energy estimations. Atoms-in-molecules (AIM) and natural bond orbital (NBO) analyses further revealed weak but stabilizing Ag–O coordination with partial covalent character, particularly stronger in gallic acid. Although modeled using a simplified 1:1 metal–ligand framework, these insights support the dual role of phytochemicals as reducing and stabilizing agents in AgNP synthesis. Together, the experimental and computational findings demonstrate that P. fascicularis extract is a promising and sustainable source for green AgNP production, with potential antimicrobial and biomedical applications.