Sulfo Cy5 Maleimide is a water-soluble, bright, far-red-fluorescent dye with excitation ideally suited for the 633 nm or 647 nm laser lines. A significant advantage to using long wavelength dyes such as Sulfo Cy5, AFDye 647 or IR 650 dye over other fluorophores is the low autofluorescence of biological specimens in this region of the spectrum.
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. Sulfo Cy5 conjugates are only recommended for detection of moderate-to-high abundance targets. For detection of low-abundance biological targets we recommend using AFDye 647 Maleimide or IR 647 Maleimide, which can attached to proteins at high molar ratios without significant self-quenching, enabling brighter conjugates and more sensitive detection.