Water soluble sulfo-Cyanine3 dye, free unactivated monofunctional carboxylic acid. This reagent can be used as a reference fluorophore for Cy3® detection channel, as a control in experiments with other sulfo-Cyanine3 labeled products. Carboxylic acid can be also activated with carbodiimides.Absorbance and emission spectra are identical with Cy3® fluorophore.