– Cyanine5.5 maleimide chloride, a CY dye, is a compound characterized by two nitrogen atoms connected by an odd number of methyl units. CY dyes exhibit long wavelengths, adjustable absorption and emission, high extinction coefficient, good water solubility, and relatively simple synthesis [1]. They are commonly used for labeling proteins, antibodies, and small molecules. For protein antibody labeling, the combination can be achieved through a simple mixing reaction, which has reference significance [2].