Photoactivatable and water soluble FRET dyes with high uncaging cross section

Photoactivatable fluorophores are powerful imaging probes for tracking molecular and cellular dynamics with high spatiotemporal resolution. We have designed and synthesized a new caged FREr dye, CCC-1, comprising a caged cournarin and a water soluble xanthene dye. CCC-1 can be efficiently photolyzed by ultraviolet light. Its photolyzed product, CC-1, emits strong green fluorescence with a FREr efficiency of 95% when excited near 410 nm. The uncaging cross section of CCC-1 is about 6000 M-1cm-1 at 365 nm, more than a hundred times higher than caged fluoresceins developed previously. The probe is also blocompatible and has built-in functionalities for bioconjugation.