Used in bioconjugation for reversible attachment of molecules in drug delivery and protein labeling. The NHS ester reacts efficiently with primary amines to form stable amide bonds, while the disulfide (SS) linker provides a cleavable site under reducing conditions, useful in intracellular release. The azide group enables click chemistry, allowing selective coupling with alkynes via CuAAC or SPAAC reactions. Commonly applied in the synthesis of antibody-drug conjugates (ADCs), targeted therapies, and functionalized nanoparticles where controlled release and modular assembly are required.