Biotin-PEG-Alk (MW 20000) is a biotin-labeled polyethylene glycol (PEG) derivative with a terminal alkyne group for efficient click chemistry applications. Biotin serves as an enzymatic cofactor, providing specific protein labeling, 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.