A caged, localizable rhodamine derivative for superresolution microscopy.

A caged rhodamine 110 derivative for the specific labeling of SNAP-tag fusion proteins is introduced. The caged rhodamine 110 derivative permits the labeling of cell surface proteins in living cells and of intracellular proteins in fixed cells. The probe requires only a single caging group to maintain the fluorophore in a non-fluorescent state and becomes highly fluorescent after uncaging. The high contrast ratio is confirmed both in bulk and at the single molecule level. This property, together with its high photon yield makes it an excellent dye for photoactivated localization microscopy (PALM), as we demonstrate here.