Cy5.5 Maleimide

Unit Size
Price (USD)
Cat.#: 1342-1
Unit size: 1 mg
in stock
Cat.#: 1342-5
Unit size: 5 mg
in stock
Cat.#: 1342-25
Unit size: 25 mg
in stock
Cat.#: 1342-100
Unit size: 100 mg
in stock

Cy5.5 Maleimide (also sold under as sulfo-Cyanine5.5 Maleimide) is a bright and photostable near-IR dye that is spectrally similar to Alexa Fluor® 680, DyLight 680™, and IRDye® 680 dye. Cy5.5 Maleimide is completely water-soluble and often a reagent of choice for labeling antibodies, peptides, and proteins that are sensitive toward organic co-solvents. Cy5.5 conjugates are pH insensitive from pH 4 to pH 10 and produces minimal autofluorescence of biological specimens in this region of the spectrum. Fluorescence of this long-wavelength Cyanine dye is not visible to the human eye but is readily detected by most imaging systems.

Maleimide is the most popular sulfhydryl-reactive reactive group for conjugating the dye to a thiol group on a protein, oligonucleotide thiophosphate, or low molecular weight ligand. The maleimide group specifically and efficiently reacts with reduced thiols (sulfhydryl groups, –SH) at pH 6.5 to 7.5 to form stable thioether bonds.

Thiol (Cys)
Abs/Em Maxima
675/694 nm
Extinction coefficient
190,000 cm-1M-1
Water, DMSO, DMF
Spectrally similar dyes
Alexa Fluor® 680, DyLight® 680, IRDye® 680
Molecular weight
Storage conditions
Shipping conditions
Ambient temperature


Enter only one — either volume or amount of protein to be labeled
Enter only one — either maximum concentration of DMSO or volume DMSO added to label

Cy®Dye is a trademark of GE Healthcare.