Synthesis of gold nanoparticles with seed enlargement size by γ-irradiation and investigation of antioxidant activity

Gold nanoparticles (AuNPs) with size in the range of 10–50 nm were synthesized by γCo-60 irradiation using water soluble chitosan (WSC) as stabilizer and size enlargement by seed approach. The maximum absorption wavelength (λmax) was measured by UV–vis spectroscopy and particle size was determined from TEM images. Results showed that value of λmax increased from 523 nm (seed particles) to 525, 537 and 549 nm and the size of AuNPs increased from 10 nm (seed particles) to 20, 38 and 53 nm for concentration ratio of [Au3+]/[Au0] (seed) of 2.5, 5 and 10, respectively. When [Au3+]/[Au0] = 20 and 40, the size of AuNPs was not further increased. Antioxidant activity of AuNPs with size of 10, 20, 38 and 53 nm was investigated using free radical 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS+). Results indicated that among the size of AuNPs tested, AuNPs of 10 nm exhibited the strongest antioxidant activity. Thus, due to the compatibility of WSC and unique property of AuNPs, AuNPs/WSC synthesized by γ-irradiation method can be potentially applied in biomedicines, cosmetics and in other fields as well.