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.