A novel colorimetric and "turn-off" fluorescent probe based on catalyzed hydrolysis reaction for detection of Cu2+ in real water and in living cells.

A novel and highly selective fluorescent 1,8-naphthalimide-based probe, 3, was designed and synthesized for rapid Cu2+ detection in a CH3CN-H2O (3:1, v/v, pH = 7.4) solution by means of a distinct hydrolysis mechanism via its Cu2+-promoting feature. Upon treatment with Cu2+, the fluorescence response of probe 3 at 550 nm abruptly decreased, which was visible to the naked eye, and this response was accompanied by a clear change of the color of the solution; the color changed from the original yellow color to colorless. This color change occurred due to the Cu2+-promoted hydrolysis of 3, which yielded a fluorescence-quenched product. It is inspiring that probe 3 exhibited excellent sensitivity, a short response time and strong anti-interference recognition. Compared with the allowable amount of Cu2+ (∼20 μM) in drinking water, the detection limit of 3 for Cu2+ is calculated to be 9.15 nM, which is much lower than the amount defined by standards. The probe can be successfully applied for the determination of Cu2+ in real aqueous samples. Furthermore, probe 3 can be used as a fluorescent sensor to detect Cu2+ in biological environments, demonstrating its low toxicity to organisms and good cell permeability in live cell imaging.