Cy5.5 is widely used in biomedical research for its near-infrared fluorescence properties, making it ideal for in vivo imaging. Its emission wavelength allows deep tissue penetration with minimal background interference, enabling real-time visualization of biological processes in living organisms. This dye is commonly conjugated to antibodies, peptides, or nanoparticles for targeted imaging of tumors, inflammation, or specific cellular markers. It is also employed in molecular imaging to track drug delivery, monitor therapeutic efficacy, and study disease progression. Additionally, Cy5.5 is utilized in flow cytometry and microscopy for high-resolution cellular and subcellular imaging. Its stability and brightness make it a valuable tool in diagnostics and preclinical research.