Simple naphthalimide-based fluorescent sensor for highly sensitive and selective detection of Cd²⁺ and Cu²⁺ in aqueous solution and living cells

A novel naphthalimide-based fluorescent sensor bearing the N,N′-bis(salicylidene)diethylenetriamine receptor was developed, which exhibited dual signaling behaviors for Cd²⁺ and Cu²⁺, and was applicable to the environmental and biological milieus. Upon addition of Cd²⁺, the fluorescence intensity enhanced in a linear fashion with the maximum fluorescence intensity increase of about 4-fold. Moreover, with the sensor 1 and 1-Cd²⁺ complex, Cu²⁺ was easily recognized by marked fluorescence quenching. The selectivity and sensitivity of the sensor 1 for Cd²⁺ were satisfactory and achieving a detection limit at the nanomolar level. The living cell image experiments demonstrated the value of sensor 1 in fluorescent visualization of Cd²⁺ ions in biological systems.