Microwave-assisted green synthesis of gold nanoparticles using MAE-derived aqueous Rubus caesius L. Fruit extract: characterization and UV–Vis spectral stability

Gold nanoparticles (AuNPs) were synthesized through a microwave-assisted green route using an MAE-derived aqueous Rubus caesius L. fruit extract as a natural reducing and stabilizing medium. The effects of precursor concentration, extract volume, and microwave power were systematically evaluated within the tested experimental range. The combination of 0.075 mM HAuCl₄0.3 H₂O, 0.4 mL fruit extract, and 180 W microwave irradiation produced the most distinct and symmetric surface plasmon resonance response. FT-IR analysis suggested that oxygen-containing functional groups in the extract may have contributed to Au³⁺ reduction and AuNP surface stabilization. TEM analysis revealed spherical, triangular, and hexagonal nanoparticles with an average core size of 11.6 ± 3.2 nm. DLS showed a hydrodynamic diameter of 71.92 ± 4.12 nm and a polydispersity index of 0.425, while the near-neutral zeta potential indicated limited colloidal stability. UV-Vis monitoring showed that the RC-AuNPs largely retained their spectral characteristics for up to 45 days. The synthesized nanoparticles exhibited a core size comparable to previously reported Rubus-mediated AuNPs. The specific contribution of this study is the use of an MAE-derived aqueous R. caesius L. fruit extract together with the systematic evaluation of key synthesis parameters affecting AuNP formation, optical response, and colloidal behavior.