TAT-PEG-Cy3 is a fluorescent labeling reagent that integrates the Cy3 fluorescent dye, a cell-penetrating peptide (TAT), and polyethylene glycol (PEG). The Cy3 fluorophore is commonly employed in applications such as immunolabeling, nucleic acid labeling, fluorescence microscopy, and flow cytometry, with a maximum emission wavelength of approximately 562–570 nm. TAT-PEG-Cy3 is suitable for cell-targeted delivery and bioimaging.