Sulfo-Cyanine5.5 amine potassium is a highly hydrophilic, water-soluble cyanine dye with four sulfonate groups, tailored for far-red/near-infrared applications including in vivo imaging. As a member of the cyanine dye family, it exhibits an impressive extinction coefficient, enhancing its brightness as a fluorescent marker in the far-red region. This amine-containing dye features an amine group linked to the fluorophore by a long linker, which aids in conjugation. The aliphatic primary amine groups can be coupled with various electrophiles (activated esters, epoxides, etc.) and are also suitable for enzymatic transamination labeling.