Cy3 NHS Ester (also sold under Sulfo-Cyanine3 NHS ester name) 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.
The NHS ester (or succinimidyl ester) is the most popular amine reactive group for labeling with the primary amines of proteins (Lys), amine-modified oligonucleotides, and other amine-containing molecules. Cy3 NHS ester is not recommended for labeling proteins at high molar ration due significant self-quenching, and only recommended for detection of moderate-to-high abundance targets. For detection of low-abundance biological targets we recommend using AFDye 555 NHS Ester (Alexa Fluor ® 555 analog), which can be attached to proteins at high molar ratios without significant self-quenching, enabling brighter conjugates and more sensitive detection.