Lipid Adsorption on MPOCs. We speculated that the
migration of phospholipid molecules from the bilayer
membrane to the MPOC surface, was responsible for the
pore formation on the membrane. Therefore, we evaluated an
ability of MPOCs to adsorb phospholipids at pH 7.4 and 5.5.
The result indicated that MPOCs could adsorb lipids at both
pH conditions but adsorption at pH 5.5 was greater than at pH
7.4 (Supporting Information, Figure S5). It should be noted
here that the zeta potential values of the MPOCs are −30.97 ±
2.06 mV and −33.31 ± 1.80 mV in pH 7.4 and 5.5 buffers,
respectively. To further investigate the involvement of lipid
adsorption on the pore generation, we tested an ability of
phospholipid-loaded MPOCs to penetrate lipid bilayer
membrane of the cell-sized liposomes. When the 2 to 1 (by
weight) phospholipid/MPOC
mixture was incubated with
cell-sized liposomes, rhodamine fluorescence signals could be
observed inside the liposomes.