Cell-penetrating peptides can associate with molecular cargo and influence uptake, but delivery claims require evidence for internalization, release and biological availability.
Cargo association and uptake
Cationic or amphipathic peptides can be linked to cargo or assemble with it through noncovalent interactions. Charge ratio, particle state, serum components and cargo size influence whether the complex remains stable long enough to reach cells.
Uptake is not the same as delivery
A fluorescent signal at the cell surface or inside an endosome does not prove cytosolic availability. Washing controls, localization studies and cargo-function readouts help distinguish adsorption, internalization and productive release.
Comparing delivery systems
Toxicity, batch reproducibility, cargo protection, endosomal escape and cell-type selectivity should be measured alongside uptake. The appropriate comparator depends on the cargo and experimental model rather than on a universal delivery ranking.
