A New Spiropyran-Based Fluorescent Probe for Dual Sensing of Ferrous Ion and pH

A new spiropyran-based fluorescent probe was developed for dual detection of Fe²⁺ ion and pH. Addition of Fe²⁺ and Ag⁺ to the probe solution enhanced the fluorescence intensity by 6 and 5 fold, respectively. Addition of Fe³⁺, Hg²⁺ and Ni²⁺ caused slight increase in the fluorescence intensity of the probe. While addition of other common metal ions did not bring about substantial change of the fluorescence. Thus the probe can be used for fluorescence turn-on detection of Fe²⁺ ion in ethanol/water (9:1) medium. The detection limit of the probe for Fe²⁺ is 0.77 µM. The suitable pH range for the probe to detect Fe²⁺ was pH 3 - 9. Other metal ions including Li⁺, Na⁺, K⁺, Ag⁺, Cu²⁺, Zn²⁺, Co²⁺, Ni²⁺, Mn²⁺, Sr²⁺, Hg²⁺, Ca²⁺, Mg²⁺, Al³⁺, Cr³⁺, and Fe³⁺ did not cause marked interference with Fe²⁺ recognition. The color of the probe solution was yellow at pH 1 - 2 and colorless at other pH values. The fluorescence intensity of the probe was low at pH 1 - 12 and increased significantly when the pH was 13 and 14, indicating that the probe can be used as a colorimetric and fluorescent probe for sensing extremely acidic or extremely alkaline conditions through different channels.