Cyanine5.5 maleimide chloride is a CY dye compound characterized by two nitrogen atoms connected through an odd number of methylene groups, exhibiting long excitation and emission wavelengths, high molar extinction coefficients, strong water solubility, and simple synthetic accessibility. Cyanine5.5 maleimide chloride is widely employed for the fluorescent labeling of proteins, antibodies, and small molecules, and the labeling process can be achieved through direct conjugation reactions that serve as a valuable reference model in bioimaging and analytical chemistry research.