FSD EX Fluor™ 555 NHS Ester is a next-generation, amine-reactive bright yellow dye developed through BioActs’ cutting-edge technology. It exhibits outstanding optical performance compared with spectrally similar dyes. After conjugation to biomolecules such as antibodies, nucleotides, and proteins, the dye maintains remarkably high fluorescence intensity, making the FSD EX Fluor™ series ideal for a wide range of biochemical and biological analytical applications. FSD EX Fluor™ 555 is particularly suitable for single-molecule detection in fluorescence correlation spectroscopy and fluorescence polarization measurements. Its excitation and emission maxima (Ex/Em = 554/565 nm) are comparable to those of Alexa 555, DyLight 549, ATTO 550, and Cy3. The dye can be efficiently excited by 532, 543, 546, or 555 nm laser lines and demonstrates excellent brightness and photostability. The NHS ester form readily reacts with amine-modified oligonucleotides or primary amines on biomolecules—such as the ε-amino group of lysine or the terminal amine of nucleotides—to form a stable amide linkage. This enables high-sensitivity labeling of low-abundance biomolecules with excellent conjugation efficiency and strong signal intensity. FSD EX Fluor™ 555 NHS Ester is supplied for labeling antibodies, peptides, proteins, ligands, and amplification substrates, and is optimized for cellular labeling and detection applications.