Biotin azide reacts with the terminal alkynes via a copper-catalyzed click reaction, including biomolecules containing alkyne groups through azide-alkyne cycloaddition. Biotin and biotin derivatives can be readily conjugated to various biomolecules through the well-known click chemistry and subsequently detected with streptavidin, avidin or NeutrAvidin biotin-binding protein. Biotin azide can be used to prepare various biotinylated conjugates via Click Chemistry. Click chemistry contains a class of chemical reactions that use bio-orthogonal or biologically unique moieties to label and detect the molecule in mild and aqueous conditions. This reagent allows labeling of various alkynylated molecules, such as DNA, oligonucleotides, and proteins with biotin. Biotin binding to avidin or streptavidin could be used in downstream affinity applications for the isolation of biotinylated molecules or their binding with streptavidin conjugates [1].

Reference:
[1] Bruckman M A, Czapar A E, VanMeter A, et al.  Tobacco mosaic virus-based protein nanoparticles and nanorods for chemotherapy delivery targeting breast cancer[J]. Journal of Controlled Release, 2016, 231: 103-113.