Colorimetric and visual sensing of ferrous ion by Fenton reaction-stimulated etching of triangular gold nanoplates

In this study, a method for ultrasensitive sensing of Fe 2+ based on Fenton reaction mediated etching of triangular gold nanoplates (Au NPLs) was developed. In this assay, the etching of Au NPLs by H 2 O 2 was accelerated in the presence of Fe 2+ due to the generation of superoxide free radical (O 2 · - ) via Fenton reaction . With the concentration of Fe 2+ increased, the shape of Au NPLs changed from triangular to sphere with the blue shifted localized surface plasmon resonance, accompanying a series of consecutive color changes from blue, bluish purple, purple, reddish purple and finally to pink. The rich color variations enable rapid visual quantitative determination of Fe 2+ within 10 min. A good linear relationship between the peak shifts and the concentration of Fe 2+ was obtained in the range of 0.035 to 1.5 μM (R 2  = 0.996). Favorable sensitivity and selectivity in the presence of other tested metal ions were achieved in the proposed colorimetric assay. The detection limits (3ơ/ k ) for Fe 2+ was 26 nM by UV–vis spectroscopy, and the clearly discernible concentration of Fe 2+ was as low as 0.07 μM by naked eyes. The recoveries of fortified samples in pond water and serum samples ranged from 96% to 106% with interday relative standard deviations <3.6% in all cases, demonstrating the applicability of the assay for measuring Fe 2+ in real samples.