Cy5 carboxylic acid is widely used in the field of biomedical research as a fluorescent labeling agent. It is particularly valuable in fluorescence microscopy and flow cytometry, where it helps in visualizing and tracking biological molecules. The compound is often conjugated to proteins, peptides, or antibodies to study cellular processes, protein interactions, and localization within cells. Its near-infrared fluorescence makes it suitable for in vivo imaging, as it penetrates tissues more effectively with minimal background interference. Additionally, Cy5 carboxylic acid is employed in diagnostic assays, such as immunoassays, to detect and quantify specific biomarkers. Its stability and bright fluorescence also make it a popular choice for developing biosensors and molecular probes.