Green chemistry approach for the synthesis of gold nanoparticles: Role of soybean extract as a bioreductant

Gold nanoparticles (AuNPs) have gained considerable attention for biomedical applications, including biosensing, imaging, drug delivery, and cancer therapy; however, conventional chemical synthesis methods often employ toxic reagents and require complex purification, limiting environmental sustainability and clinical translation. Green chemistry provides an eco-friendly alternative through the use of biogenic reducing agents and benign solvents. In this study, AuNPs were synthesized by reducing chloroauric acid (HAuCl 4 ) using sodium citrate and soybean ( Glycine max ) extract under acidic (pH 3.0), physiological (pH 7.4), and alkaline (pH 8.5) conditions. The soybean extract, prepared via ethanol extraction and rotary evaporation, served as a reducing agent due to its high content of polyphenols, flavonoids, and carbohydrates. The synthesized AuNPs were characterized by UV–Vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and dynamic light scattering (DLS). Surface plasmon resonance bands appeared at 537–589 nm, with soybean-mediated AuNPs exhibiting blue-shifted peaks and higher absorbance compared to citrate-derived nanoparticles, indicating smaller particle sizes and higher yields. SEM confirmed predominantly spherical nanoparticles below 50 nm, while XRD revealed a crystalline face-centered cubic structure. FTIR analysis demonstrated the involvement of soybean phytochemical functional groups in nanoparticle reduction. DLS results showed smaller hydrodynamic diameters (108–149 nm) for soybean-derived AuNPs relative to citrate-based counterparts, with optimal stability at pH 7.4. These findings highlight soybean extract as a sustainable, low-cost bioreductant for green AuNP synthesis with potential biomedical and catalytic applications.