An ''off-on-off'' sensor for sequential detection of Cu 2+ and hydrogen sulfide based on a naphthalimide-rhodamine B derivative and its application in dual-channel cell imaging.

A novel colorimetric and fluorometric sensor with unique dual-channel emission to sequentially detect Cu 2+ and hydrogen sulfide (H 2 S) was synthesized from naphthalimide-rhodamine B through the PET and FRET mechanism. The sensor showed a selective "off-on" fluorescence response with a 120-fold increase toward Cu 2+ , and its limits of detection were 0.26 μM and 0.17 μM for UV-vis and fluorescence measurements, respectively. In addition, 1-Cu 2+ was an efficient "on-off" sensor to detect H 2 S with detection limits of 0.40 μM (UV-vis measurement) and 0.23 μM (fluorescence measurement), respectively. Furthermore, the sensor can also be used for biological imaging of intracellular staining in living cells. Therefore, the sensor should be highly promising for the detection of low level Cu 2+ and H 2 S with great potential in many practical applications.