A Reversible Colorimetric and Fluorescence "Turn-Off" Chemosensor for Detection of Cu²⁺ and Its Application in Living...

Dual-function chemosensors that combine the capability of colorimetric and fluorimetric detection of Cu²⁺ are still relatively rare. Herein, we report that a 3-hydroxyflavone derivative (E)-2-(4-(dimethylamino)styryl)-3-hydroxy-4H-chromen-4-one (4), which is a red-emitting fluorophore, could serve as a reversible colorimetric and fluorescence "turn-off" chemosensor for the detection of Cu²⁺. Upon addition of Cu²⁺ to 4 in neutral aqueous solution, a dramatic color change from yellow to purple-red was clearly observed, and its fluorescence was markedly quenched, which was attributed to the complexation between the chemosensor and Cu²⁺. Conditions of the sensing process had been optimized, and the sensing studies were performed in a solution of ethanol/phosphate buffer saline (v/v = 3:7, pH = 7.0). The sensing system exhibited high selectivity towards Cu²⁺. The limit of naked eye detection of Cu²⁺ was determined at 8 × 10^-6 mol/L, whereas the fluorescence titration experiment showed a detection limit at 5.7 × 10^-7 mol/L. The complexation between 4 and Cu²⁺ was reversible, and the binding constant was found to be 3.2 × 10⁴ M^-1. Moreover, bioimaging experiments showed that 4 could penetrate the cell membrane and respond to the intracellular changes of Cu²⁺ within living cells, which indicated its potential for biological applications.