Used in bioconjugation to link biomolecules such as proteins, peptides, or antibodies with other functional groups, especially in drug delivery systems and diagnostic probes. The NHS ester reacts efficiently with primary amines to form stable amide bonds, while the azide group allows for click chemistry, such as copper-catalyzed azide-alkyne cycloaddition (CuAAC), enabling modular assembly of complex biomolecular constructs. Commonly applied in the development of antibody-drug conjugates (ADCs), surface immobilization on biosensors, and PEGylation to improve solubility and stability of therapeutic molecules. The long, hydrophilic PEG6 spacer reduces steric hindrance and enhances binding efficiency in crowded molecular environments.