A cap-type Schiff base acting as a fluorescence sensor for zinc(II) and a colorimetric sensor for iron(II), copper(II), and zinc(II) in aqueous media

A simple and low cost chemosensor is described. This sensor could simultaneously detect three biologically important metal ions through fluorogenic (Zn(2+)) and chromogenic (Fe(2+), Cu(2+), and Zn(2+)) methods in aqueous solution. The sensor could function as a "turn-on" fluorescence receptor only to Zn(2+) ions. In addition, the sensor could be successfully applied to the detection of intracellular Zn(2+). Meanwhile, the sensor displayed an obvious red color upon selective binding with Fe(2+). Therefore, the sensor could serve as a useful tool for the discrimination of Fe(2+) from Fe(3+) in aqueous media. Moreover, the sensor also showed color changes from yellow to colorless upon selective binding with Zn(2+) and Cu(2+), respectively. The detection limit of the sensor for Cu(2+) (1.5 μM) is far below the guidelines of the World Health Organization (30 μM) as the maximum allowable copper concentration in drinking water, and therefore it is capable of being a practical system for the monitoring of Cu(2+) concentrations in aqueous samples. These results provide a new approach for selectively recognizing the most important three trace elements in the human body simultaneously, for Zn(2+) by emission spectra and Fe(2+), Cu(2+), and Zn(2+) by the naked eye.