Used as a reactive fluorescent dye in biological imaging and labeling applications. Its sulfonate and carboxylic acid groups enhance water solubility and allow conjugation to proteins, antibodies, or nucleic acids through carbodiimide chemistry. Commonly employed in flow cytometry, fluorescence microscopy, and immunoassays due to strong absorption and emission in the near-infrared range, enabling low-background detection in complex biological samples. Stable under physiological conditions and compatible with live-cell imaging.