Mitochondria-Accessing Ratiometric Fluorescent Probe for Imaging Endogenous Superoxide Anion in Live Cells and Daphnia magna

Superoxide anion (O2•–), as the precursor of other reactive oxygen species (ROS), is significantly important in the maintenance of redox homeostasis and various cellular signaling pathways. Here we present a ratiometric mitochondria-accessing fluorescent probe (NA-T) based on nucleophilic substitution mechanism for real-time measuring O2•–. By regulating the intramolecular charge of 1,8-naphthalimide, a ratiometric response model was obtained, which evinced 18-fold enhancement of fluorescence ratio (I540 nm/I475 nm) in the presence of O2•– over other ROS with rapid response (132 s), high sensitivity (DL = 0.370 μM) and selectivity. Confocal fluorescence images demonstrated that the probe could well permeate through plasma membrane for visualizing endogenous O2•– changes in mitochondria of living cells and in inflammatory Daphnia magna, indicating NA-T a potential tool for the diagnosis and research of corresponding diseases.