Surface potential of lipid aggregates. The ζ-potentials of aggregates made of LPS () or phospholipids () are plotted versus the net charge of the respective lipid molecules. ζ-potentials were measured in buffer containing 10 mM Tris, 2 mM CsCl2 and pH7. The lipid concentration was 0.01 mM. The net charges were calculated from the chemical structures determined by mass spectrometry.