Determination of antioxidant activities in fruit juices based on rapid colorimetric measurement and characterisation of gold nanoparticles

Abstract

A simple and green synthesis of gold nanoparticles (AuNPs) was achieved in tea solution and fruit juices with auric tetrachloride (HAuCl₄) without the addition of any other chemicals. Natural antioxidants present in tea leaves and fruit juices were able to reduce Au³⁺ ions to form AuNPs spheres with an average diameter of 22.9 ± 2.7 nm in the tea solution and 12.8 ± 2.4 nm in the orange juice. A colorimetric determination of antioxidant activities based on the formation of citrate-capped AuNPs has been developed. It was found that the colorimetric response of AuNPs was dependent on the concentration of antioxidants tested. As compared with the standard reference assay, i.e., the Folin–Ciocalteu method, the colorimetric method reported in this study showed a very good correlation (R² = 0.9996). The results indicate that the AuNPs-based colorimetric method provides a simple, effective and reliable measurement of the antioxidant capacity in the tested fruit juices.

Keywords:

• gold nanoparticles
• antioxidant activity
• UV-Vis spectroscopy
• green synthesis

Acknowledgements

The authors greatly appreciate the helpful discussions with Dr. Austin Raabe.

Additional information

Funding

This research is supported by the Office of Research and Sponsor Programs Grant (#11099D) from Florida Gulf Coast University.