A biotin probe for copper-free click chemistry reaction, Biotin-PEG4-DBCO reacts with azides to form a stable triazole and does not require Cu-catalyst or elevated temperatures. Often a reagent of choice in live cell surface glycans and lipids studies where the presence of cytotoxic copper catalyst is not acceptable. In application where the presence of copper is a concern Biotin-PEG4-DBCO is an ideal alternative to copper requiring biotin-alkynes.