Water soluble sulfo-Cyanine3.5 dye, free unactivated monofunctional carboxylic acid. This reagent can be used as a reference fluorophore for Cy3.5® detection channel, as a control in experiments with other sulfo-Cyanine3.5 labeled products. Carboxylic acid can be also activated with carbodiimides.Absorbance and emission spectra are identical with Cy3.5® fluorophore.