A novel turn on fluorescent probe based on a hybrid carbazole-cyanine platform was designed and synthesized for detecting hydroxyl radicals in living cells.

The CCy-OH probe had exhibited ideal properties including fast response (0.5 min), good selectivity, and low cytotoxicity.

Almost 60-fold fluorescence enhancement was obtained when the probe was treated with OH in solution with excitation at 510 nm and emission at 604 nm.

Fluorescence imaging shows that the novel CCy-OH probe is membrane-permeable and suitable for detecting endogenous hydroxyl radicals in living cells.