AFDye™ 555 Picolyl Azide (Alexa Fluor® 555 Picolyl Azide replacement) is an advanced fluorescent probe that incorporates a copper-chelating motif to raise the effective concentration of Cu(I) at the reaction site. The rate of CuAAC reaction depends on concentrations of all reagents, including copper, thus the raise of the effective copper concentration at the reaction site dramatically increase the rate of CuAAC reaction without the need to increase concentration of azide reagent and copper.
In addition, the use of picolyl azides instead of conventional azides allows for at least a tenfold reduction in the concentration of the copper catalyst without sacrificing the efficiency of labeling.
In summary, the introduction of a picolyl moiety into an azide probe leads to a substantial increase in the sensitivity of alkyne detection. This will be of special value for the detection of low abundance targets or where significant increase in signal intensity is desired.