A ratiometric fluorescent probe for the detection of endogenous hydroxyl radicals in living cells

A new ratiometric fluorescent probe (4) for monitoring hydroxyl radicals (•OH) has been designed and synthesized. The ratiometric sensing of probe 4 toward •OH is realized by the oxidation of the dicyanovinyl group of probe 4 to afford the corresponding epoxide, which can further reaction with •OH to give a coumarin derivative as the final product. The above reaction interrupts the large π-conjugated system of probe 4 and exhibits a remarkable large blue shift of 160 nm in the emission spectra of the sensing system. Probe 4 exhibits high selectivity toward •OH over other reactive oxygen species and reactive nitrogen species. Preliminary study shows that probe 4 can be employed to monitor endogenous •OH in living cells with a ratiometric fluorescent imaging manner.