Sulfo Cy5-tetrazine sodium is a tetrazine-coupled Cy5 derivative dye with fluorescence properties similar to CY5 (Ex/Em=633/647 nm). Sulfo-Cy5-tetrazine sodium is a click chemistry reagent, it contains a Tetrazine group that can undergo an inverse electron demand Diels-Alder reaction (iEDDA) with molecules containing TCO groups.