Fluorescence detection of melamine based on inhibiting Cu2+-induced disaggregation of red-emitting silver nanoclusters.

Herein, we report a facile method to synthesize red-emitting, water-soluble Ag nanoclusters (Ag NCs) employing lipoic acid as a stabilizing agent. The Ag NCs show aggregation-induced emission property and have good stability and optical properties. Cu2+ can disperse the aggregated Ag NCs, accompanied by the quenching of fluorescence. However, the formed Cu2+-melamine complex by the coordination chemistry between free copper ion and melamine is able to effectively avoid the quenching process of Cu2+ to the Ag NCs. Hence, the Ag NCs can be applied to design a novel fluorescent probe based on this property to detect melamine. In the determination of melamine, the as-prepared fluorescent Ag NCs exhibit favorable sensitivity and high selectivity. The limit of detection (LOD) down to 0.022 mg/L and good recoveries of real sample experiments were obtained. This fluorescent probe is proved to be convenient and rapid for detecting melamine, with potential application to trace melamine analysis in complicated samples.