SPDP-PEG4-COOH is widely used in bioconjugation and protein modification due to its ability to link molecules through amine and thiol groups. The SPDP moiety allows for selective crosslinking with thiol-containing molecules, while the PEG4 spacer enhances solubility and reduces steric hindrance, making it ideal for creating stable and functional conjugates. This compound is particularly useful in antibody-drug conjugates (ADCs), where it facilitates the attachment of cytotoxic drugs to antibodies, improving targeted drug delivery. Additionally, it is employed in the development of peptide and protein-based therapeutics, enabling precise modifications to enhance stability, bioavailability, or targeting capabilities. Its application extends to diagnostic tools, where it aids in labeling biomolecules for imaging or detection purposes.