Cy5.5 PEG is one of Nanocs' near infrared fluorescent PEG dyes with different chemical reactive or bioactive moieties. Cy5.5 is a bright cyanine dye with excitation/emission around 680 nm/701 nm. Nanocs PEG modified Cy5.5 dyes offer better water solubility, less steric hindrance and enhanced stability. Reactive groups all these dyes enable them to react with proteins, antibodies or enzymes easily and efficiently.