Calcium Ions Turn on the Fluorescence of Oxytetracycline for Sensitive and Selective Detection

Herein, we report an interesting finding about the new application of oxytetracycline (OTC), as a fluorescent probe for the detection of calcium ion (Ca²⁺), which proved that it can offer an expeditious, highly sensitive, and selective detection method for Ca²⁺. Upon the addition of Ca²⁺, the fluorescence of OTC could be significantly enhanced with rapid response and high sensitivity, and achieved a good limit of detection as low as 125 nM in aqueous solution. The complex formed via Ca²⁺ coordinating to the hydroxyl group of OTC contributes to the fluorescence enhancement, which has been proved by several characterization methods including UV-vis analysis, binding constant determination, and fluorescence titration. The method avoided complexity for EDTA measurement of Ca²⁺ in running water as proposed previously. Taking advantage of good availability, stability and operability, the OTC was further successfully applied to the detection of Ca²⁺ in a real environment. Graphical Abstract.