Insights into the structure of gold nanoparticles synthesized via natural polyphenols: A green chemistry approach

Gold nanoparticles (AuNPs) have gained significant attention due to their unique physicochemical properties and wide range of applications. However, conventional synthesis methods often rely on toxic reducing agents, raising environmental and safety concerns. This study presents a green synthesis approach for AuNPs using three structurally diverse natural polyphenols—curcumin, quercetin, and rutin—as both reducing and stabilizing agents. The synthesized AuNPs were comprehensively characterized using UV–Vis and fluorescence spectroscopy, DLS, TEM, XRD, FTIR, ¹H NMR, and XPS. The results revealed that the structure of each polyphenol significantly influenced nanoparticle size, morphology, and surface chemistry. Curcumin-AuNPs exhibited strong metal-ligand interactions through the β-diketone and phenolic –OH groups. Quercetin-AuNPs showed a balance of electrostatic and metal-ligand interactions due to its catechol structure. Rutin-AuNPs displayed excellent monodispersity due to steric stabilization from its bulky glycosidic chains. The disappearance of characteristic FTIR and ¹H NMR signals in the AuNP systems confirmed strong chemisorption of the polyphenols on the gold surface. These findings demonstrate a green and versatile method for gold nanoparticle synthesis and provide mechanistic insights into the interaction of natural polyphenols with gold surfaces. To the best of our knowledge, this is the first comparative study that systematically evaluates curcumin, quercetin, and rutin side-by-side in the green synthesis of gold nanoparticles, providing mechanistic insights into how structural diversity within a single polyphenol family governs nanoparticle formation and stabilization.