Cy5.5 maleimide is widely used in biomedical research for labeling proteins, peptides, and antibodies due to its ability to selectively bind to thiol groups. This property makes it particularly valuable in fluorescence imaging and microscopy, where it helps visualize and track biomolecules in live cells or tissues. Its near-infrared emission range allows for deeper tissue penetration and reduced background fluorescence, making it ideal for in vivo imaging studies, such as tumor targeting and tracking drug delivery systems. Additionally, it is employed in flow cytometry and immunoassays to detect and quantify specific biomolecules with high sensitivity.