Atto 425-NHS ester is widely used in fluorescence labeling of biomolecules such as proteins, peptides, and antibodies. Its NHS ester group reacts efficiently with primary amines under mild conditions, forming stable amide bonds, making it ideal for conjugation without disrupting the biological activity of the target molecule. Due to its high fluorescence quantum yield and good photostability, it is particularly useful in fluorescence microscopy, including confocal and super-resolution imaging. It is also employed in flow cytometry and fluorescence-based immunoassays where bright, consistent signals are required. The dye’s excitation and emission profile in the blue-green region allows for easy integration with common laser lines and filter sets, and it can be used in multiplex experiments alongside other fluorophores. Additionally, it is suitable for labeling nucleic acids when conjugated to amine-modified oligonucleotides.