Sulfo-Cy series fluorescent dyes (e.g., Sulfo-Cy3, Sulfo-Cy5, Sulfo-Cy7, etc.) are sulfonated derivatives of cyanine (Cy) dyes, offering enhanced water solubility and excellent biocompatibility. They are widely used in applications such as biomolecular labeling, immunofluorescence, flow cytometry, and in vivo imaging. Sulfo-Cy dyes incorporate sulfonate groups (–SO₃⁻) into the Cy dye structure, significantly improving their solubility in aqueous solutions. They can be directly dissolved in buffers or water without requiring organic co-solvents (e.g., DMSO), simplifying experimental procedures and minimizing toxicity to biological samples