Used in bioconjugation and surface modification due to its reactive azide group and hydrophilic PEG chain. The terminal azide allows for click chemistry, particularly copper-catalyzed azide-alkyne cycloaddition (CuAAC), enabling efficient coupling with alkyne-functionalized biomolecules, nanoparticles, or surfaces. The long octa(ethylene glycol) spacer reduces non-specific binding, improves solubility in aqueous environments, and enhances the mobility of attached molecules. Commonly applied in the development of biosensors, diagnostic assays, drug delivery systems, and functionalized coatings where controlled molecular orientation and low fouling are critical.