Colorimetric determination of radical scavenging activity of antioxidants using Fe3O4 magnetic nanoparticles

We report the first use of iron oxide magnetic nanoparticles (Fe3O4 MNPs) as a novel, alternative, simple and reliable agents for colorimetric measurement of radical scavenging activity of the antioxidants. In the presence of H2O2 and the peroxidase colorimetric substrate, Fe3O4 MNPs catalyzed the oxidation of colorless peroxidase substrate to form colorimetric products via the generation of hydroxyl radicals. After adding antioxidants, the catalytic activity of Fe3O4 MNPs was inhibited due to scavenging of hydroxyl radicals by the antioxidants, producing less colorimetric products resulting in the reduction of color intensity. Two model antioxidant standards including gallic acid (GA) and epigallocatechin gallate (EGCG) were successfully evaluated for their hydroxyl radical scavenging activity using the developed assay. The performance of the developed method was validated against traditional antioxidant assays for 9 tea samples. Using the Spearman rank correlation coefficient method, the antioxidant activity of tea samples obtained from the Fe3O4 MNP assay correlated well with the traditional assays at the 95% confidence level. Furthermore, the developed assay was successfully carried out on a paper-based device to provide for high throughput analysis with low amounts of reagents and sample consumption and low analysis cost for screening of radical scavenging activity of the antioxidants. The results from the analysis of antioxidant activity in tea samples obtained from the Fe3O4 MNP paper-based assay were not significantly different to those obtained from the developed Fe3O4 MNP spectrophotometric assay indicating that the developed assay was also applicable in a low-cost analysis platform.

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