Figure 1. Click chemistry labeling

Standard CuAAC reactions
Azides and alkynes can be used interchangeably in standard CuAAC reactions, so either one can serve as the tagged substrate or be labeled for the detection step. Some biomolecules are sensitive to the amount of copper used to catalyze standard click reactions. In particular, proteins such as GFP and R-PE exhibit reduced fluorescence and nucleic acids can be denatured by a high-copper environment.

Picolyl azides for low-copper reactions
Picolyl azide reagents enable researchers to perform copper-catalyzed click reactions with compounds that are sensitive to copper, while retaining all of the benefits of the original azide/alkyne click reaction. Picolyl azide only need much lower copper concentration than standard click reactions to protect against undesired copper side reactions with proteins (e.g., GFP, RPE), nucleic acids (e.g., RNA, oligos), and even small molecules (e.g., phalloidin). Additionally the picolyl azides can be used to increase sensitivity or accelerate the reactions by using the original copper-catalyzed reaction conditions.

DBCO alkynes for copper-free reactions
DBCO reagents can be used to perform click reactions with azide-modified targets without the use of heavy metal catalysis. DBCO reactions are ideal for surface labeling of live cells and also minimize damage to fluorescent proteins like GFP or R-PE.

CLICKable Biotin and Fluorescent Dye Selection Guide