The in vivo incorporation of alkyne-modified bases into the genome of cells is today the basis for the efficient detection of cell proliferation. Cells are grown in the presence of ethinyl-dU (EdU), fixed and permeabilised. The incorporated alkynes are then efficiently detected by using azide-containing fluorophores and the Cu^I-catalysed alkyne–azide click reaction. For a world in which constant improvement in the sensitivity of a given method is driving diagnostic advancement, we developed azide- and alkyne-modified dendrimers that allow the establishment of sandwich-type detection assays that show significantly improved signal intensities and signal-to-noise ratios far beyond that which is currently possible.