Polycations have been used as nonviral gene carriers because the polycations and DNAs form stable complexes in a noncovalent manner (1 –3 ). The polycations, e.g., poly(L-lysine) (PLL), are reported to be conjugated with several ligands for targeted gene delivery (4 –8 ). The physicochemical properties of the DNA complexes have been described as factors that influence transfection activity (9 –11 ).
