Green synthesis of gold nanoparticles from Pfaffia glomerata extracts for enhanced electrode modification and antimicrobial applications.

Gold nanoparticles (AuNPs) are widely used in pharmaceuticals, diagnostics, textiles, and energy. Plant extracts have become a promising green alternative for AuNP synthesis. Pfaffia glomerata (Brazilian ginseng) contains phenolics and saponins that serve as reducing and stabilizing agents in green synthesis. In this study, for the first time, aqueous extracts from the root, stem, leaf, and flower of P. glomerata were applied to synthesize AuNPs. A 22 factorial design optimized experimental conditions, using hydrodynamic diameter from dynamic light scattering (DLS) as the response variable. Optimized conditions were 0.5 mmol at 40 °C for root, 1.0 mmol at 40 °C for stem and leaf, and 0.5 mmol at 50 °C for flower. Nanoparticle formation was confirmed by UV-Vis spectroscopy through surface plasmon resonance bands. DLS revealed hydrodynamic diameters of 88.1 nm (root), 41.0 nm (stem), 76.7 nm (leaf), and 30.4 nm (flower). TEM showed that nanoparticle morphology depended on the plant part used. FTIR-ATR confirmed phenolic involvement in synthesis and stabilization. Electrochemical tests indicated that carbon paste electrodes modified with AuNPs, except those from leaf extracts, showed improved performance and potential for sensor development. Antimicrobial assays revealed that AuNPs from root, leaf, and flower extracts inhibited Candida albicans growth. These results demonstrate P. glomerata's potential as a sustainable source for green synthesis of functional AuNPs for biomedical and electrochemical applications.