Colorimetric determination of Hg(II) by combining the etching and aggregation effect of cysteine-modified Au-Ag core-shell nanorods

[Display omitted] A simple and effective approach for colorimetric detection of Hg2+ based on surface etching and aggregation effect of cysteine-modified Au-Ag core-shell nanorods has been investigated. Both the intensity decrease and wavelength shift of the LSPR peak could be used in Hg2+ sensing, which greatly enlarges the detection range. •Both the intensity decrease and wavelength shift of the LSPR has been used in sensing.•The effect of aggregation and etching depends on the mercury ions concentration.•The red shift has a large detection range for mercury ions from 60 to 250μM.•The surface etching effect-induced red shift of LSPR leads to vivid color change. In this report, a simple and effective approach for colorimetric detection of Hg2+ based on surface etching and aggregation effect of cysteine-modified Au-Ag core-shell nanorods has been investigated. When the addition of Hg2+ has a low concentration under 60μM, electrostatic interaction-induced intense aggregation of colloidal Au-Ag core-shell nanorods takes place. Thus the longitudinal plasmonic absorption peak decreases rapidly, which also leads to the colloidal color become shallow. Whereas when the addition of Hg2+ has a high concentration greater than 60μM, the adherent cysteine molecules break away from the surface of nanorods due to the intense Hg-S bond. Then the bare nanorods have been etched under the action of Hg2+. The decrease of the Ag shell results in the red shift of the longitudinal absorption peak, which further leads to the color change of the colloids. The sensing based on particle aggregation-induced absorption decrease has a linear response for Hg2+ from 1 to 60μM with a theoretical detection limit of 0.273μM. The sensing based on etching effect-induced red shift has a logarithmic response for Hg2+ from 60 to 250μM with a theoretical detection limit of 1.065μM. Interference test and real samples detection results show that Hg2+ could be specifically detected by using this probe based on Au-Ag core-shell nanorods.