A nucleus targetable fluorescent probe for ratiometric imaging of endogenous NO in living cells and zebrafishes

Nitric oxide (NO) is an important cellular messenger molecule in the cardiovascular, nervous and immune systems. Real-time monitoring of NO activity in specific organelles of live cells is important to understand its biological function. In this work, a nucleus targetable ratiometric NO probe, Hoe-Rh-NO, is developed by linking Hoechst to rhodamine spirolactam. The Hoechst part conducts nucleus targeting and the rhodamine spirolactam senses NO. The two fluorophores constitute a NO switchable FRET system for ratiometric imaging. This newly developed probe Hoe-Rh-NO displays good nucleus target-ing ability, high sensitivity and selectivity towards NO, low cytotoxicity and most importantly indicates NO through rati-ometric fluorescence imaging. By using Hoe-Rh-NO, we confirmed the presence of NO in the nucleus and indicated endoge-nous NO during inflammation in cells and zebrafishes.