Photostable and printable fluorescence carbon quantum dots for advanced message encryption and specific reversible multiple sensing of Cu2+ and cysteine

The ability to manipulate carbon quantum dots (CQDs) fluorescence with specific substances has been of primary importance for applications in advanced dynamic information encryption. The development of CQDs with specific functionalization, high selectivity and excellent fluorescence stability for information security and sensing remains a challenge. In this paper, we present an N -doped and tryptophan functionalized CQDs that can be applied not only as a fluorescent ink for multiple message encryption but also for fluorescent sensitive and selective recognition of Cu 2+ and cysteine (Cys) by multi-method, including aqueous solutions, filter paper, hydrogels and in human DU-145 Prostate cancer cells. Theoretical calculations and mechanistic studies suggested that this on–off-on mechanism was attributed to the transfer of electrons between Cu 2+ and functionalized groups on the surface of CQDs and stronger coordination capability with Cys. The above results showed that these newly designed CQDs will greatly enrich the fundamental understanding of CQDs by explaining the recognition mechanism between Cu 2+ and Cys, and provide an opportunity for anti-counterfeiting, solid-state fluorescent materials, cellular imaging and environmental.