Phase transfer mechanisms of fluorophore-labeled cell-penetrating peptide ε-poly-l-α-lysine at liquid|liquid interfaces

•The interfacial (membrane permeation) mechanism of the fluorescence-labeled FAM-εPL was elucidated via the PMF technique.•For membrane translocations of cargos, the covalent approach is rather important than the electrostatic interaction with polycationic εPL.•Phase transfer of εPL-FAM was accelerated through the interaction with the polar head group of phospholipid layer.