Antioxidant and catalytic reduction activity of green synthesized gold nanoparticles using water-soluble chitosan

Gold nanoparticles (AuNPs) were synthesized with water-soluble chitosan serving as the reducing agent and stabilizer. Subsequently, they were characterized by UV–vis, TEM, FT-IR, and XRD. The impact of water-soluble chitosan concentration and molecular weight on the morphology of the synthesized AuNPs was investigated. The in vitro antioxidant activity of AuNPs against OH·, ABTS·+, DPPH, and NO· was assessed. Additionally, the catalytic reduction activity of AuNPs toward 4-nitrophenol (4-NP) in the presence of NaBH4 was evaluated. The results indicated that various morphologies, including spherical, anisotropic AuNPs, and triangular Au nanoplates with different particle sizes, could be synthesized by controlling the concentration and molecular weight of water-soluble chitosan. It was discovered that the antioxidant and catalytic reduction activity of AuNPs were correlated with their morphology. Spherical AuNPs with a particles diameter of 15 nm exhibited the highest antioxidant activity, with estimated IC50 values of 24.6 ± 1.9, 15.6 ± 3.2, 22.6 ± 1.9, and 15.1 ± 1.9 μg/mL for OH·, ABTS·+, DPPH, and NO·, respectively. Triangular Au nanoplates showed the highest reaction rate constant of0.3889 min−1 and turnover frequency of 7.52 × 10−5mol/(mg·min), as well as the lowest activation energy of 24.1 kJ/mol.