A novel fluorescent probe based on naphthalimide and nile blue for selective recognition of Cu2+ and pH

A dual responsive and "turn-on" fluorescent probe NapL with large Stokes shift (115 nm) and large fluorescence emission (585 nm) was designed, synthesized and investigated. NapL has high selective and suitable sensitive (LOD = 82.6 nM) towards Cu2+ over a wide pH range (7.4–12.1) through a fluorescence "turn-on" mechanism and with rapid response to Cu2+ (30 s) in complex environments. Furthermore, NapL is sensitive toward pH changes within range (7.4–2.1) with obvious "turn - on" effect (about 37- fold). The sensitive detection characteristics of Cu2+ can be ascribed to the coordination performance of N and O atoms to Cu2+, whereas pH responsiveness is ascribed to the protonation of imino group. NapL has been made into convenient and low-cost pH test strip for detecting pH range (7.4–2.1), and it has also been successfully used for the detection of Cu2+ in MCF-7 breast cancer cells under neutral conditions.