In this work, we present a new type of functional organic/inorganic hybrid supraparticle that spontaneously assembles from silver ions (Ag+), iodide ions (I−) and thioflavin T (ThT) under aqueous solution conditions. ThT alone in aqueous solution was weakly fluorescent with an emission band at 494 nm, which was related to the monomer. However, in the above-mentioned hybrid supraparticle (i.e., ThT@AgI SP) structure, the ThT monomer can form a dimer with a new emission band. The new band shifted to 546 nm and the emission intensity increased. We further present a facile strategy of reversible fluorescence switching of ThT by a simple cation (Ag+) and anions (I− and S2−), which can be employed for the ratiometric fluorescence detection of Ag+ with high sensitivity and selectivity. The linear range of detecting Ag+ was from 100 nM to 10 μM, with a limit of detection as low as approximately 50 nM. Moreover, it can be successfully applied for the operation of a logic gate system and to the sensing of Ag+ in real water samples.
