The Cy7 azide can be reacted with terminal alkynes via a copper-catalyzed click reaction (CuAAC). It also reacts with strained cyclooctyne via a copper-free “click chemistry” reaction to form a stable triazole and does not require Cu-catalyst or elevated temperatures. Cy7 is a far-red (near-infrared) emitting dye with a peak excitation at 753 nm and maximum emission at 776 nm in PBS. Cy7 is spectrally almost identical to other near-IR dyes, including of Alexa Fluor® 750, DyLigh®t 750, or IRDye™ 750.