Bis-(N,N'-amine-PEG3)-Cy5 TFA salt is a PEG linker containing a cyanine dye with excitation/emmission maximum 649/667 nm and a free amine group, which will be reactive with cabroxylic acid, activated NHS ester, carbonyl (ketone, aldehyde) etc. The hydophilic PEG spacer increases solubility in aqueous media.