Sulfo-Cyanine 3 NHS is widely used in bioconjugation for labeling biomolecules such as proteins, peptides, and antibodies. Its primary application lies in fluorescence-based detection and imaging due to its strong absorption and emission in the visible range, making it ideal for fluorescence microscopy, flow cytometry, and immunoassays. The NHS ester group reacts efficiently with primary amines on biomolecules under mild aqueous conditions, forming stable amide bonds. The sulfo group enhances water solubility and reduces nonspecific binding, which improves signal-to-noise ratio in biological assays. It is especially useful in cell surface labeling and protein interaction studies where high fluorescence intensity and low background are critical.