A Sensitive “Turn-On” Fluorescent Sensor for Melamine Based on FRET Effect between Polydopamine-Glutathione Nanoparticles and Ag Nanoparticles

In this work, Ag nanoparticles (AgNPs) were synthesized quickly by a one-step method utilizing polydopamine-glutathione nanoparticles (PDA-GNPs) as a reducing agent. The PDA-GNPs and the generated AgNPs acted as the energy donor and acceptor, respectively. Accordingly, the fluorescence of PDA-GNPs was quenched on the basis of fluorescence resonance energy transfer (FRET). In the presence of melamine, the preferential combination of Ag(I) and melamine to form Ag(I)–melamine complex prevents Ag(I) from forming AgNPs, together with fluorescence enhancement compared with the absence of melamine. Under the optimal conditions including the concentration of AgNO3, reaction time, reaction temperature, and pH, the fluorescence enhancement efficiency has a linear response to the concentration of melamine from 0.1 to 40 μM with a detection limit of 23 nM for melamine. The proposed method is simple, time-saving, and low-cost, which was further applied to detect melamine in real milk products with satisfactory results.