Bis-PEG25-NHS ester is widely used in bioconjugation and crosslinking applications due to its ability to form stable bonds with primary amines in proteins, peptides, and other biomolecules. Its long PEG spacer enhances solubility and reduces steric hindrance, making it ideal for modifying biomolecules in drug delivery systems, where it improves pharmacokinetics and reduces immunogenicity. Additionally, it is employed in surface modification of nanoparticles and materials to enhance biocompatibility and stability. The NHS ester group ensures efficient and selective coupling, making it a valuable tool in the development of targeted therapies, diagnostic agents, and biomaterials.