Phytochemical Profiling and Green Synthesis of Silver Nanoparticles from Quercus robur Acorn: Characterization and Biological Evaluation

Silver nanoparticles (AgNPs) were synthesized via a green approach using aqueous extract of Quercus robur acorn as a reducing and stabilizing agent. The synthesis process was optimized at 1 mM Ag+ concentration, yielding stable nanoparticles with a characteristic surface plasmon resonance peak at 445 nm. Structural and morphological analyses confirmed the formation of predominantly spherical nanoparticles with particle sizes ranging between 40 and 68 nm and a face-centered cubic crystalline structure. Phytochemical analyses revealed significantly higher total phenolic and total flavonoid contents in the crude acorn extract compared to the synthesized nanoparticles, indicating the involvement of these compounds in the phytoreduction process. Although antioxidant activity decreased after nanoparticle formation, phyto-mediated AgNPs (PAgNPs) exhibited notable antibacterial activity, particularly against Staphylococcus aureus with a minimum inhibitory concentration of 26 µg/mL. Antibiotic combination assays demonstrated additive and synergistic interactions depending on the tested microorganism. Gas Chromatography–Mass Spectrometry (GC–MS) analysis of acorn essential oil identified β-caryophyllene (43.1%) as the major component, suggesting the presence of bioactive terpenoids potentially contributing to nanoparticle stabilization. These findings demonstrate that Quercus robur acorn extract can serve as suitable phytogenic source for the controlled synthesis of silver nanoparticles with moderate antibacterial potential.