Green synthesis and characterization of gold nanoparticles using anthocyanins from Rubus palmeri

BACKGROUND: The green synthesis of nanoparticles based on noble metals has been researched in the last decades. The physical and optical properties of gold, along with the metabolites found in plant extracts that work as capping agents, allow the development of materials that can be used in alternative therapies in human health. OBJECTIVE: This study reports the obtention of gold nanoparticles (AuNPs) through a green synthesis process, using purified anthocyanins (ACNs) from Rubus palmeri berries as reducing and stabilizing agents. RESULTS: The colloidal solution obtained with a ratio of 1.6 mg: 0.6 mM (ACNs:HAuCl4) was monitored through UV-Vis spectroscopy over 10 h at 30°C, producing a surface plasmon resonance (SPR) signal at 540 nm. The interaction between the ACNs and the AuNPs was analyzed through Fourier-transform infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) determined an average size of 13 nm with a spherical morphology predominance at 30°C, while at 20°C triangular morphologies appeared. Energy-dispersive X-ray spectroscopy (EDX) and elemental mapping showed predominance of the gold element. The antioxidant activity was analyzed by ORAC and ABTS assays, showing a variation of up to four times the EC50 between the AuNPs and the ACNs. CONCLUSION: These results determined the role of ACNs in the green synthesis of AuNPs and their capability to induce various morphologies at different temperatures.