Used in bioconjugation to link biomolecules such as proteins, peptides, or antibodies with high selectivity. The NHS ester reacts efficiently with primary amines, forming stable amide bonds, while the azide group enables click chemistry, particularly copper-catalyzed azide-alkyne cycloaddition (CuAAC), for modular assembly of complex biomolecular constructs. PEG12 spacer enhances water solubility, reduces aggregation, and increases the flexibility and biocompatibility of the conjugate. Commonly applied in the development of antibody-drug conjugates (ADCs), targeted therapeutics, diagnostic probes, and functionalized nanoparticles. Also used in surface modification of biosensors and microarrays where controlled immobilization is required.