Cy5 carboxylic acid (non-sulfonated)

Cy5 carboxylic acid is a non-activated carboxylic acid with low aqueous solubility. For coupling with amines, or protein labeling, Cy5 NHS ester and water-soluble sulfo-Cy5 NHS ester is preferred. This labeling dye has limited water solubility. For biomolecule labeling, the labeling reagent 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.

In the cells, The Cy5 carboxylic acid label on the dye can track the efficiency of the protein expression [1].

Reference:
[1] Deyle, K. M.; Farrow, B.; Hee, Y.Q.; Work, J.; Wong, M.; Lai, B.; Umeda, A.; Millward, S.W.; Nag, A.; Das, S.; Heath, J.R. A protein-targeting strategy used to develop a selective inhibitor of the E17K point mutation in the PH domain of Akt1. Nature Chemistry,2015, 7, 455–462.