N-(m-PEG4)-N'-(m-PEG4)-O-(m-PEG4)-O'-(azide-PEG4)-Cy5 is a PEG linker containing a cyanine dye with excitation/emmission maximum 649/667 nm as well as an azide group, which enables Click Chemistry. The hydophilic PEG spacer increases solubility in aqueous media.
