This chemical is widely used in bioconjugation and labeling applications due to its dual functionality. The NHS ester group allows for efficient covalent attachment to primary amines, making it ideal for labeling proteins, peptides, and antibodies. The m-PEG4 spacer enhances solubility and reduces steric hindrance, improving the performance of the labeled biomolecules in various assays. The Cy5 fluorophore is a near-infrared dye, enabling its use in fluorescence microscopy, flow cytometry, and in vivo imaging, where deeper tissue penetration and minimal background fluorescence are required. Its PEGylated structure also helps reduce immunogenicity, making it suitable for therapeutic and diagnostic applications.