Biotin-PEG-Alk (MW 20000) is a biotin-labeled polyethylene glycol (PEG) derivative featuring a terminal alkyne group for efficient click chemistry applications. Serving as an enzymatic cofactor, biotin provides specific labeling of proteins, while the hydrophilic PEG moiety offers solubility and low toxicity. The alkyne functionality enables copper-catalyzed azide-alkyne cycloaddition (CuAAC), enhancing target binding through reaction with azide-modified molecules.