MTX-PEG-Cy3 is a Cy3-labeled MTX-PEG conjugate. Cy3 fluorophore is frequently utilized in applications such as immunolabeling, nucleic acid labeling, fluorescence microscopy, and flow cytometry, with a maximum emission wavelength of approximately 562-570 nm. Methotrexate (Amethopterin; MTX) serves as an antimetabolite and antifolate agent that inhibits dihydrofolate reductase, preventing the conversion of folic acid to tetrahydrofolate and ultimately inhibiting DNA synthesis. Additionally, Methotrexate functions as an immunosuppressant and antineoplastic agent, deployed in the treatment of rheumatoid arthritis and the investigation of various cancers, including acute lymphoblastic leukemia.