An ''off-on-off'' sensor for sequential detection of Cu2+ 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 Cu2+ and hydrogen sulfide (H2S) 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 Cu2+, and its limits of detection were 0.26 μM and 0.17 μM for UV-vis and fluorescence measurements, respectively. In addition, 1-Cu2+ was an efficient "on-off" sensor to detect H2S 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 Cu2+ and H2S with great potential in many practical applications.