An in vitro comparison of the antioxidant activities of chitosan and green synthesized gold nanoparticles

Gold nanoparticles (AuNPs) were synthesized using chitosan with different degree of deacetylation (DD) and molecular weight (MW) as reducing agent and stabilizer. The synthesized AuNPs were characterized by UV-vis spectroscopy, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffractometer (XRD). The OH, ABTS⁺ and DPPH scavenging activity and ferric reducing antioxidant power (FRAP) of chitosan, synthesized AuNPs and Au colloids were determined through in vitro assays. The antioxidant activity of chitosan decreased with the decreasing of chitosan DD and concentration, while increased with the decreasing of chitosan MW. Low molecular weight chitosan (LMWC, 47.8 kDa) showed the highest antioxidant activity at concentration of 0.3% (w/v). The antioxidant activities of AuNPs were dependent on their size, shape and amount. Spherical AuNPs showed the higher antioxidant activity than irregular or polygonal ones. The antioxidant activities of Au colloids were dependent on the DD, MW and concentration of chitosan. Au colloids synthesized by 0.3% (w/v) LMWC (47.8 kDa) showed the highest antioxidant activity. Compared with chitosan and Au colloids, the improved antioxidant activity of Au colloids may be due to the synergistic effect of AuNPs and chitosan remained in the colloids.