Modulating fluorescence emission of l-methionine-stabilized Au nanoclusters from green to red and its application for visual detection of silver ion

Gold nanoclusters (Au NCs) have been considered as novel heavy metal ions sensors due to their ultrafine size, photo-stability and excellent fluorescent properties. This work not only demonstrated a novel strategy to modulate the emission color of l-methionine stabilized Au NCs based on a unique manner of Ag(Ⅰ) adding, but successfully applied this strategy for visual detection of Ag(Ⅰ) in environmental water samples. The Au NCs prepared here had yellow-green fluorescence with emission peaks at 536 nm. When Ag(Ⅰ) was added, the emission peak showed a clear shift from 538 nm to 590 nm and the color showed a change from yellow-green to orange. The Ag(Ⅰ) of concentration from 18.0 to 210.0 μM could be linearly detected using this method with a limit of detection (LOD) of 8.54 μM. The formation mechanisms of these Au NCs was discussed and the strategy proposed here was promising for preparing new types of fluorescent metal nanoclusters and a new analytical method.