– Biotin-PEG-azide (MW 2000) is a biotinylated polyethylene glycol (PEG) compound featuring an azide group. Biotin serves as an enzyme cofactor suitable for protein labeling. PEG, noted for its hydrophilicity and water solubility, exhibits low toxicity. The azide functionality is a reasonably effective leaving group that participates in copper-catalyzed reactions with alkynes, enhancing the binding efficiency to biotin’s targets.