A 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 M) 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.