Sulfo-Cyanine5.5 is a water-soluble, hydrophilic fluorophore which possesses emission in far red area of the spectrum, an analog of Cy5.5®. As other cyanine dyes, sulfo-Cyanine5.5 has an outstanding molar extinction coefficient which gives rise to its bright fluorescence. The molecule contains four sulfo groups that provide hydrophilicity and negative charge to the fluorophore - this minimizes non-specific binding. The azide group of sulfo-Cyanine5.5 azide can be conjugated with terminal alkynes in the presence of copper(I) catalyst, or with cycloalkynes in copper free strain promoted reaction. Spectral properties： Excitation/absorption maximum, nm: 673 ε, L⋅mol−1⋅cm−1: 211000 Emission maximum, nm: 691 Fluorescence quantum yield: 0.21 CF260: 0.09 CF280: 0.11