A Reversible Colorimetric and Fluorescence “Turn-Off” Chemosensor for Detection of Cu(2+) and Its Application in Living Cell Imaging

Dual-function chemosensors that combine the capability of colorimetric and fluorimetric detection of Cu(2+) 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 Cu(2+). Upon addition of Cu(2+) 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 Cu(2+). 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 Cu(2+). The limit of naked eye detection of Cu(2+) 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 Cu(2+) was reversible, and the binding constant was found to be 3.2 × 10(4) M(−1). Moreover, bioimaging experiments showed that 4 could penetrate the cell membrane and respond to the intracellular changes of Cu(2+) within living cells, which indicated its potential for biological applications.