A quinoline-fluoran hybrid fluorescent probe for selectively and sensitively sensing copper ions and fluorescence imaging application

Developing fluoran dyes as fluorescent probes is interesting because it is of great significance to extend their applications from the printing industry to other fields such as fluorescence analysis and medicine. We here present a new quinoline-fluoran hybrid dye QF, which delivers fluorescent signals in water (pH: 4.0 - 9.0) with the maximum absorption and emission centered at 514 nm and 597 nm, respectively. In addition, a large Stokes shift (83 nm) can be observed when compared to that of rhodamine B. QF is further employed for the preparation of a new fluorescent probe QFH, which exhibits high selectivity towards copper ions with the limit of detection down to 1.54 nM via a Cu2+-triggered spirolactam ring opening and hydrolysis process. Significantly, QFH can be applied for the detection of copper ions at physiological pH conditions (pH: 6.0 - 9.0) and shows low cell cytotoxicity, which allows it to be a candidate for tracing Cu2+ by cell imaging.