Ratiometric fluorescent determination of cysteine based on organic nanoparticles of naphthalene–thiourea–thiadiazole-linked molecule

Novel ratiometric fluorescent cysteine probes based on naphthalene–thiourea–thiadiazole (NTTA) fluorescent organic nanoparticles (FONs) were designed and synthesized. NTTA FONs show good water solubility, high selectivity for sensing and a 74 nm red-shift of fluorescence emission upon binding cysteine in aqueous media are observed. Under optimum condition, linear relationships are found between the relative fluorescence intensity ratio I430/I356 and the logarithmic concentration of cysteine in the range of 0–100 μM with the detection limit was found to be 1.5 × 10−9 M, while the FL intensity of NTTA FONs to other amino acids is negligible. The possible mechanism is discussed.