Quantification of the Cellular Uptake of Cell‐Penetrating Peptides by MALDI‐TOF Mass Spectrometry

The ins and outs of peptides: The internalization efficiencies of three cell-penetrating peptides (CPPs; penetratin, (Arg)9, and Tat48–59) have been measured by MALDI-TOF MS (see scheme). The method leads to direct detection of the CPPs and allows unambiguous discrimination between membrane-bound and internalized CPP. Furthermore, the cellular uptake efficiencies of several CPPs can be compared in a single experiment.