A simple turn-off fluorescent chemosensor based on a Schiff base structure for ultrafast and highly selective trace detection of Cu ions in aqueous solutions.

A simple turn-off fluorescent probe, 5-(diethylamino)-2-(hydrazonomethyl)phenol (DHP), is designed and synthesized for the sensitive and selective detection of Cu. The bright green fluorescence of DHP is quenched after the addition of Cu. The probe DHP exhibits good anti-interference performance against Cu in the presence of multiple metal ions. The fluorescence intensity of DHP (10 μM) at 522 nm is well linearized with the Cu concentration at 0-5 μM, and it has a detection limit of 0.29 nM ( = 0.9949). The complexation ratio of the probe DHP to Cu is 2 : 1 and the complexation constant is 3.44 × 10 M ( = 0.9974). In addition, the probe DHP can be recovered using EDTA and Cu can be effectively monitored at pH 5-11, with good results in dipstick experiments and actual water samples. HepG-2 cells remained viable in excess of 90% after being exposed to DHP (50 μM) for 24 h, which demonstrates the extremely low toxicity of DHP, and it can be used for cell imaging.