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 (Zn²⁺) and chromogenic (Fe²⁺, Cu²⁺, and Zn²⁺) methods in aqueous solution. The sensor could function as a "turn-on" fluorescence receptor only to Zn²⁺ ions. In addition, the sensor could be successfully applied to the detection of intracellular Zn²⁺. Meanwhile, the sensor displayed an obvious red color upon selective binding with Fe²⁺. Therefore, the sensor could serve as a useful tool for the discrimination of Fe²⁺ from Fe ³⁺ in aqueous media. Moreover, the sensor also showed color changes from yellow to colorless upon selective binding with Zn²⁺ 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 Cu²⁺ 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 Zn²⁺ by emission spectra and Fe²⁺, Cu²⁺, and Zn²⁺ by the naked eye.