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

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 60 μM, 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 60 μM, 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 60 μM with a theoretical detection limit of 0.273 μM. The sensing based on etching effect-induced red shift has a logarithmic response for Hg²⁺ from 60 to 250 μM with a theoretical detection limit of 1.065 μM. 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.