Plasmonic nanoprobes based on the shape transition of Au/Ag core-shell nanorods to dumbbells for sensitive Hg-ion detection.

We report a sensitive and selective localized surface plasmon resonance (LSPR) nanoprobe for the detection of mercuric ions (Hg 2+ ) using gold/silver core-shell nanorods as an optical nanosubstrate. Sulfide can quickly react with silver atoms to generate Ag 2 S at room temperature in the presence of oxygen. The transformation from Ag shell to Ag 2 S on the nanorod surface results in its LSPR absorption band shifting to a longer wavelength, which is attributed to their different refractive indices. Interestingly, the morphology also changed from a rod-like to dumbbell shape. However, in the presence of Hg 2+ , this morphology transformation is inhibited because the sulfide reacts with free Hg 2+ prior to the Ag atoms. The amount of Ag 2 S reduced with the increasing concentration of Hg 2+ , and the absorption band shift was also decreased. According to this "rod-like to dumbbell or not" shape change, a sensitive and selective LSPR nanoprobe was established, assisted by UV-Vis absorption spectroscopy. The detection limit of this probe for Hg 2+ was as low as 13 nM. The efficiency of this probe in complex samples was evaluated by the detection of Hg 2+ in spiked water samples.