endo-BCN-PEG2-acid is used in bioconjugation and drug delivery systems as a linker molecule to attach targeting ligands or therapeutic agents to biomolecules. The carboxylic acid group enables conjugation via amide bond formation with amines on proteins or other biomolecules. Its endo-BCN group facilitates efficient, catalyst-free click chemistry reactions, particularly with azide-containing compounds, allowing precise and rapid conjugation. The PEG2 spacer enhances water solubility, reduces steric hindrance, and improves the stability and efficacy of the final conjugate. It is widely applied in the development of antibody-drug conjugates (ADCs), targeted cancer therapies, and diagnostic probes, offering controlled and site-specific modifications.