Sulfo-Cyanine5 NHS ester is widely used in biological research for labeling proteins, peptides, and other biomolecules due to its excellent water solubility and fluorescence properties. It is particularly valuable in fluorescence microscopy, flow cytometry, and in vivo imaging, where it helps visualize and track molecular interactions and cellular processes. The NHS ester group allows for efficient conjugation to primary amines, making it a reliable tool for creating stable fluorescent probes. Its near-infrared emission is advantageous for deep tissue imaging, minimizing background autofluorescence and enhancing signal clarity. Additionally, it is employed in drug delivery studies to monitor the distribution and uptake of therapeutic agents in real time.