Alkyne-bearing targets
Identify whether the target carries a terminal alkyne or a strained alkyne such as DBCO. Terminal alkynes require a CuAAC catalyst system with an azide dye; DBCO supports copper-free SPAAC. Ordinary amines or thiols cannot directly replace either reaction partner.
Azide-bearing targets
Both PEG4-DBCO and PEG12-DBCO label azide-bearing targets. Use each product’s molecular weight to match molar input, then compare labeling density, background and function after purification. Remove free azide-functionalization reagent and check storage buffers for sodium azide.