Cy7.5 carboxylic acid is a free un-activated NIR dye which has low aqueous solubility. As for coupling and labeling reactions, pre-activated Cy7 NHS ester or water-soluble sulfo-Cy7 NHS ester would be considered. For biomolecule labeling, the labeling regent has low aqueous solubility, using of organic co-solvent to dissolve this molecular is necessary for efficient reaction. First, Cyanine dye should be dissolved in organic solvent and then added to a solution of biomolecule in appropriate aqueous buffer.
