Synthesis of carbon dots and their application as a turn off–on fluorescent sensor for trace Cu2+ and phenylalanine

Carbon dots (CDs) have drawn increasing interest due to their unique optical properties and promising application in various fields. In this study, o–Phenylenediamine and taurine were used to prepare yellow-emitting fluorescent carbon dots (Y-CDs) by a hydrothermal method, applied as novel fluorescent probes. The Y-CDs were characterized by TEM, XRD, XPS, FTIR, UV–Vis and fluorescence spectroscopy. The results showed that the obtained uniform Y-CDs were spherical with an average size of 3.8 nm, and the surfaces were rich in hydrophilic groups, causing the good water phase stability. Their optimal excitation wavelength was 380 nm with an emission wavelength of 580 nm. The effect of different cations on the fluorescence of carbon dots was investigated in a phosphate solution at pH 7.4. It was found that the Y-CDs can be used to selectively detect Cu²⁺ using a ‘turn off’ mechanism and phenylalanine (Phe) using a ‘turn on’ mechanism with detection limits of 0.188 µM and 0.584 µM, respectively, much lower than those reported relating to the previous CDs. Obviously, these Y-CDs can be used as an ideal analytical platform for detecting trace Cu²⁺ and Phe, and have potential applications especially in the fields of environmental protection and human health.