A multicolor colorimetric assay for sensitive detection of sulfide ions based on anti-etching of triangular gold nanoplates

Abstract

This study presents a viable colorimetric assay for sensitive sensing of sulfide ions (S2−) using triangular gold nanoplates (AuNPLs) as nanoprobes. The sensing mechanism is based on regulating the etching process of AuNPLs upon the addition of different concentration of S2−. In the presence of Cu2+ and I−, the AuNPLs would be etched by triiodide ions (I3−) produced from the redox reaction between Cu2+ and I−, resulting in the transformation of the shape of AuNPLs from triangular into sphere and blue shifted localized surface plasmon resonance (LSPR). However, in the presence of S2−, a preferential reaction between Cu2+ and S2− occurred, and the inhibition of the formation of I3− prevented the AuNPLs from being etched. Correspondingly, a red shift of LSPR can be observed with an increase of the concentration of S2−, accompanying a readily distinguishable color transition that goes from pink to purplish red, purple, bluish purple and blue. The color alterations allow for a visual estimation of the concentrations of S2−, and the lowest visual concentration through naked-eyes was 0.1 μM. A good linear relationship (R2 = 0.997) between the peak shifts and the concentration of S2− was obtained in the range of 0.02–1.5 μM, and the limit of detection (3 s/k) by UV–vis spectroscopy was as low as 16 nM. The as-established assay displayed excellent selectivity, which was successfully applied for analysis of S2− in environmental water samples.