AZDye™ 555 NHS Ester is a water-soluble, bright orange-fluorescent dye with excitation ideally suited for the 532 nm or 555 nm laser lines and visualized with TRITC (tetramethylrhodamine) filter sets. AZDye™ 555 conjugates of antibodies, peptides, and proteins are pH insensitive from pH 4 to pH 10. Proteins can be labeled with AZDye 555 NHS Ester at high molar ratios without significant self-quenching, leading to brighter conjugates and more sensitive detection. AZDye™ 555 conjugates ideally suited for detection of low abundance targets. The NHS Ester reacts specifically and efficiently with a primary amine at pH 7-9 to form a stable, covalent amide bond. The NHS ester (or succinimidyl ester) is the most popular tool for conjugating dyes to the primary amines of protein or antibody (Lys), amine-modified oligonucleotides, and other amine-containing molecules.