The red-fluorescent Alexa Fluor® 594 azide can be reacted with terminal alkynes via a copper-catalyzed click reaction. Click chemistry describes a class of chemical reactions that use bio-orthogonal or biologically unique moities to label and detect a molecule of interest using a two-step procedure. The two-step reaction procedure involves a copper-catalyzed triazole formation of an azide and an alkyne. Click reactions have several characteristics: the reaction between the detection moieties is efficient; no extreme temperatures or solvents are required; the reaction product is stable; the components of the reaction are bioinert; and perhaps most importantly, no side reactions occur – the label and detection tags react selectively and specifically with one another. Unlike traditional chemical reactions utilizing succinimidyl esters or maleimides that target amines and sulfhydryls – functional groups that are not unique – click chemistry-labeled molecules can be applied to complex biological samples and be detected with unprecedented sensitivity due to extremely low background.