Biotin-PEG-Alk (MW 10000) is a biotinylated polyethylene glycol (PEG) derivative with an alkyne group designed for click chemistry applications. Combining biotin, an enzyme co-factor used in protein labeling, with PEG, a hydrophilic, water-soluble, and low-toxicity polymer, the alkyne moiety enables copper-catalyzed azide-alkyne cycloaddition (CuAAC) with azido-containing molecules, enhancing the efficiency of targeting biotin-binding entities.