RGD-PEG-Cy3 is a fluorescent labeling reagent that combines the Cy3 fluorescent dye, peptide (RGD), 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 peak emission wavelength of approximately 562-570 nm. RGD is a peptide sequence (CRGDKGPDCiRGD) that targets tumor tissues specifically by binding to αvβ3 and αvβ5 integrin receptors, which are involved in tumor neovascularization.