Synthesis of Silver Nanoparticles by Using Quercus Robur Knopper Gall Extracts

Galls of the Cynipidae, such as the Knopper gall, are abnormal plant outgrowths induced by insect activity. These structures not only protect the developing larvae but also alter the biochemical properties of host plant tissues. In this study, we report the green synthesis of silver nanoparticles (AgNPs) using ethanolic extracts of <i>Quercus robur</i> Knopper galls. AgNPs were synthesized via reduction of AgNO₃ and characterized using ATR-FTIR analysis, UV-Vis spectrophotometry, powder X-ray diffraction (PXRD), and transmission electron microscopy (TEM). The UV-Vis analysis showed a strong surface plasmon resonance (SPR) peak at 418 nm. A face-centered cubic (fcc) crystalline structure with an average crystallite size of about 12 nm was verified by PXRD patterns. TEM imaging revealed well-dispersed spherical nanoparticles, consistent with the size obtained via PXRD. ATR-FTIR analysis indicated the involvement of polyphenolic and protein-related functional groups in reduction and stabilization. The synthesized AgNPs exhibited strong growth inhibition capacity against <i>B. subtilis</i> and <i>S. aureus,</i> and moderate capacity against <i>E. coli</i> and <i>P. aeruginosa.</i> These findings highlight the potential of Knopper gall extract as a sustainable source for the eco-friendly synthesis of biologically active nanoparticles.