Flavones Fluorescence-Based Dual Response Chemosensor for Metal Ions in Aqueous Media and Fluorescence Recovery

Responsiveness of sensing materials 3-hydroxyflavone (3HF) towards metal ions in aqueous medium has been explored following photoexcitation. 3HF exhibited both colorimetric and fluorescence (FL) turn-off response towards Cu²⁺ and Fe²⁺ with high sensitivity and selectivity. Meanwhile, the distinct colour change and the rapid quenching of FL intensity provide naked-eye detection. On successive addition of Cu²⁺and Fe²⁺ ions, FL of 3HF was "turned off," whereas there is no change in wavelength of FL bands. Quenching efficiencies for Cu²⁺and Fe²⁺ ions are 88% and 49%, respectively. The detection limit of the sensor towards Cu²⁺ and Fe²⁺ was 1.54 μM and 1.98 μM, respectively. The binding strategy between 3HF and metal ions (Cu²⁺, Fe²⁺) and the nature of quenching have been explored with the Benesi-Hildebrand and Stern-Volmer plots, respectively. The FL of 3HF significantly quenched in the presence of Cu²⁺ ions, and then recovered upon addition of HCl, providing the possibility of constructing a sensitive Cu²⁺-HCl off-on fluorescent probe. Moreover, the proposed simple, quick response and visual test strip-based chemosensor could be used for the detection of Fe²⁺ and Cu²⁺ ions.