Extinction Coefficient Excitation Maximum: 107000; N-methyl-N'-(hydroxy-PEG2)-Cy5 is a cyanine labeled PEG derivative with excitation/emmission maximum 649/667 nm containing hydroxyl group, which enables further derivatized or replaced with other reactive functional groups. Hydophilic PEG spacer increases solubility in aqueous media and reduces steric hindrance during binding.