Sulfo-Cy5 picolyl azide is a fluorophore that contains both a sulfonic acid group and an azide group. The azide group acts as a handle for click chemistry, allowing it to react with terminal alkynes and strained cyclooctynes [such as BCN or DBCO]. Cy5 is a cyanine dye with excitation and emission maxima at 651 nm and 670 nm, respectively. The sulfonic acid groups on the Cy5 dye enhance the compound's water solubility.