Dye-Labeled Polyacryloyl Hydrazide–Ag Nanoparticle Fluorescent Probe for Ultrasensitive and Selective Detection of Au Ion

[Image: see text] The efficiency of a fluorescence sensing device based on metal-enhanced fluorescence (MEF) is dependent on the optimization of interaction between the fluorophore and the metal nanoparticle (NP). Herewith, ultrasensitive and selective turn-on sensing of Au(3+) is achieved by using a suitable combination of fluorophore and metal NP system through sequential MEF effect. Dansyl hydrazide-tagged Ag NPs in the polyacryloyl hydrazide cavity are utilized to sense the picomolar concentration of Au(3+) in aqueous media. We demonstrated that the selective Au(3+) sensing is due to the selective deposition of Au on the Ag NP surface over the 16 other metal ions studied. The sensitivity is assigned to the strong overlapping of the emission band of the fluorophore with the surface plasmon band of the Au and improvement of fluorescence signal through successive MEF by Ag and Au colloids. The sensing is associated with a fivefold increase in fluorescence intensity and appearance of violet color of the solution. These luminescent Ag–Au bimetallic NPs may be utilized to trace cancer cells in biological systems and for cell imaging applications.