N-(m-PEG4)-N'-(PEG4-NHS ester)-Cy5 is a cyanine labeled PEG linker with excitation/emmission maximum 649/667 nm containing a NHS ester group, which is an amine reactive group. Hydophilic PEG spacer increases solubility in aqueous media. This reagent can be utilized to produce Cyanine-labeled biomolecules for subsequent use such as in vivo research, and drug design related experiments.