Synthesis of triazolo-thiadiazole fluorescent organic nanoparticles as primary sensor toward Ag and the complex of Ag as secondary sensor toward cysteine

Fluorescent organic nanoparticles (FONs) have received considerable attention in the past few years, since the material holds great flexibility in materials synthesis and optical properties. In this study, we report a novel Ag⁺-selective turn-on fluorescent chemosensor based on the triazolo-thiadiazole (TTD) FONs, which show a significant fluorescence enhancement to silver ions among fourteen metal ions due to the formation of Ag–FONs cation complex, and also exhibit a lowest detectable concentration of 2.87 × 10⁻⁹ M. Upon the addition of Cysteine (Cys), a thiol-containing amino acid, the fluorescence intensity of the colloidal solution decreases significantly with a limit detection concentration of 2.58 × 10⁻⁷ M, indicating that Cys can form the Ag–Cys complex. Thus FONs are a potential primary sensor toward Ag⁺ and a secondary sensor toward Cys. The method is a basis for further two-component recognition study of TTD FONs. The possible mechanism is also discussed.