Cy3 Maleimide (also sold under Sulfo-Cyanine3 Maleimide) is a bright, water-soluble, and pH insensitive from pH 4 to pH 10 orange-fluorescent dye. Cy3 conjugates of antibodies, peptides, and proteins can be excited using the 532 nm or 555 nm laser line and visualized with TRITC (tetramethylrhodamine) filter sets. Cy3 conjugates give less background than TAMRA and most other commonly used fluorescent dyes.
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. We do not recommended using Cy3 Maleimide for labeling proteins at high molar ration due significant self-quenching. Cy3 conjugates are only recommended for detection of moderate-to-high abundance targets. For detection of low-abundance biological targets we recommend using AF 555 Maleimide (Alexa Fluor ® 555 analog), which can attached to proteins at high molar ratios without significant self-quenching, enabling brighter conjugates and more sensitive detection.