Superior Photoprotection of Cyanine Dyes with Thio-imidazole Amino Acids

Preventing fluorophore photobleaching and unwanted blinking is crucial for singlemolecule fluorescence studies. Reductants achieve photoprotection via quenching excited tripletstates, yet either require counteragents, or for popular alkyl-thiols, are limited to cyanine dye Cy3 protection. Here we provide mechanistic and imaging results showing that the naturally occurring amino acid ergothioneine and its analogue dramatically enhance photostability for Cy3, Cy5 and their conformationally restrained congeners, providing a biocompatible universal solution for demanding fluorescence imaging.