Methyl-PEG4-NHS Ester is widely used in bioconjugation and chemical modification processes. It serves as a linker molecule to attach polyethylene glycol (PEG) chains to proteins, peptides, or other biomolecules, enhancing their solubility, stability, and biocompatibility. This modification is particularly useful in drug delivery systems, where PEGylation helps reduce immunogenicity and prolong the circulation time of therapeutic agents in the body. Additionally, it is employed in the development of antibody-drug conjugates (ADCs) and other targeted therapies, improving their efficacy and reducing side effects. The NHS ester group enables efficient coupling with primary amines, making it a valuable tool in bioconjugation chemistry.