Cy5.5 is widely used in biomedical research and diagnostics due to its near-infrared fluorescence properties. It is particularly valuable in in vivo imaging, as its emission wavelength penetrates tissue more effectively than visible light, allowing for deeper imaging with minimal background interference. This makes it ideal for tracking tumor growth, monitoring drug delivery, and studying biological processes in live animals. Additionally, Cy5.5 is commonly conjugated to antibodies, peptides, or other targeting molecules for specific labeling of cells or biomarkers in fluorescence microscopy and flow cytometry. Its stability and brightness also enhance its utility in multiplex assays, where multiple fluorescent dyes are used simultaneously.