Mussel-inspired polydopamine-encapsulated carbon dots with dual-emission for detection of 4-nitrophenol and Fe3.

Carbon dots (CDs) with excellent optical properties are widely used in biomedicine, fluorescence sensing and light emitting diodes (LEDs). However, it is still a challenge to prepare CDs that can stably emit red fluorescence in the water environment. In this study, the CDs@PDA with encapsulating structure was synthesized from p-phenylenediamine-derived red-light CDs as the core through using the mussel-inspired chemical properties of polydopamine (PDA) at room temperature. It was found that in the binary system of water/ethanol=1: 3 (volume ratio), the as-prepared CDs@PDA had a dual-emission of ultraviolet light (330 nm) and red light (640 nm) with the fluorescence quantum yields of 8.0 and 15.5 %, respectively, at the same time under the excitation of 285 nm. The as-prepared CDs@PDA can be directly used for the fluorescence selective sensing of 4-nitrophenol (4-NP) and Fe3+ through simultaneously quenching ultraviolet and red fluorescence based on the internal filtration effect mechanism with the detection limits of 3.44 and 3.75 μM, respectively. This research showed that the PDA-coated CDs can significantly improve the photoluminescence stability of CDs with new optical features. This means that the encapsulated structure of mussel chemistry is very helpful for expanding the application range of CDs in the water environment.