Azido-PEG4-NHS is an amine-reactive crosslinker designed to facilitate efficient and flexible bioconjugation and bio-orthogonal labeling in complex biological systems. This reagent contains an N-hydroxysuccinimide (NHS) ester, which selectively and efficiently reacts with primary amines on proteins, peptides, or amine-functionalized surfaces under mild aqueous conditions, forming stable amide linkages. The terminal azide moiety enables highly selective and high-yield coupling via copper-catalyzed azide-alkyne cycloaddition (CuAAC) or Staudinger ligation with phosphine-functionalized molecules, making it adaptable for a wide range of labeling and conjugation strategies.

The incorporation of a PEG4 (polyethylene glycol) spacer imparts hydrophilicity and reduces steric hindrance, which enhances solubility and enables the conjugation of larger biomolecules while minimizing potential disruptions to biological function. Azido-PEG4-NHS is particularly advantageous for applications in protein and antibody labeling, site-specific drug conjugation, and nanoparticle surface functionalization, as the PEG4 spacer optimizes spatial orientation and molecular accessibility.