FastClick™ Digoxigenin (DIG) Azide contains both the CAG moiety of FastClick (for assisting click efficiency) and DIG hapten (as the detection tag) for developing DIG-based probes. It readily reacts with an alkyne-containing biomolecule under extremely mild conditions. DIG is a steroid found exclusively in the flowers and leaves of the plants Digitalis purpurea, Digitalis orientalis and Digitalis lanata. It is a commonly used hapten (a small molecule with high antigenicity) that finds utilities in biological detections similarly to other popular haptens such as 2,4-Dinitrophenol (DNP) and biotin. DIG conjugates and tags are widely used in fluorescence imaging, fluorescence in situ hybridization (FISH) and other nucleic acid detections. FastClick™ reagents have been developed by the scientists of AAT Bioquest for enhancing the yield and reaction speed of copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. They contain a copper-chelating ligand that significantly stabilizes the Cu(I) oxidation state and thus accelerates the click reaction. They do not require the use of an external copper-chelator (such as the common THPTA or BTTAA). The high concentration of copper chelators is known to have a detrimental effect on DNA/RNA, thus causing biocompatibility issues. The introduction of a copper-chelating moiety at the reporter molecule allows for a dramatic raise of the effective Cu(I) concentration at the reaction site and thus accelerates the reaction. Under extremely mild conditions the FastClick™ azides and alkynes react much faster in high yield compared to the corresponding conventional CuAAC reactions. Click chemistry was developed by K. Barry Sharpless as a robust and specific method of ligating two molecules together. Two important characteristics make click chemistry attractive for assembling biomolecules. First, click reactions are bio-orthogonal, thus the click chemistry-functionalized biomolecules would not react with the natural biomolecules that lack a clickable functional group. Second, the reactions proceed with ease under mild conditions, such as at room temperature and in aqueous media.