A Lysosome-Targeting Fluorescence Off-On Probe for Imaging of Nitroreductase and Hypoxia in Live Cells.

A lysosome-targeting fluorescent off-on probe has been developed by one-step synthesis for detecting lysosomal nitroreductase and hypoxia. The probe is constructed by incorporating morpholine (a lysosome-targeting unit) into 4-nitro-1,8-naphthalimide (as a fluorochrome and specific substrate for nitroreductase), and the detection mechanism is based on the nitroreductase-catalyzed reduction of the probe to 4-amino-1,8-naphthalimide, accompanied by a large fluorescence enhancement at a wavelength of 543 nm. The probe shows an accurate lysosome-targeting ability with high selectivity and sensitivity to nitroreductase (detection limit: 2.2 ng mL