Used in bioconjugation to link molecules via amine groups, especially in drug delivery and protein labeling. The NHS ester reacts efficiently with primary amines to form stable amide bonds. The PEG3 spacer improves solubility and reduces aggregation, while the propargyl group enables click chemistry, such as copper-catalyzed azide-alkyne cycloaddition. Commonly applied in creating antibody-drug conjugates, fluorescent probes, and functionalized surfaces for biosensors. Stable in aqueous solution for short-term use, best used fresh or stored dry at low temperature.