A thiocarbonate-caged fluorescent probe for specific visualization of peroxynitrite in living cells and zebrafish

Peroxynitrite (ONOO-), a highly reactive oxygen species (ROS), is implicated with many physiological and pathological processes including cancer, neurodegenerative diseases and inflammation. In this regard, developing effective tools for highly selective tracking of ONOO- is urgently needed. Herein, we constructed a concise and specific fluorescent probe NA-ONOO for sensing ONOO by conjugating an ONOO--specific recognition group ((4-methoxyphenylthio)carbonyl, a thiocarbonate derivative) with a naphthalene fluorophore. The probe, NA-ONOO, was in a dark state because the high electrophilicity of (4-methoxyphenylthio)carbonyl disturbs the intramolecular charge transfer (ICT) in the fluorophore. Upon treatment with ONOO-, the fluorescent emission was sharply boosted (quantum yield Phi: 3% to 56.6%) owing to an ONOO- triggered release of (4-methoxyphenylthio)carbonyl from NA-ONOO. Optical analyses showed that NA-ONOO presented high selectivity and sensitivity toward ONOO-. With good cell permeability and biocompatibility, the NA-ONOO probe was successfully applied to imaging and tracing exogenous and endogenous ONOO- in living cells and zebrafish. The probe NA-ONOO presents a new recognition group and a promising method for further investigating ONOO- in living systems.