A, The formed nanocomplexes composed of PBAE polymers > 7 kDa and plasmid DNA reporter were incubated in cell culture medium (pH 7.4) at 37° C and changes in size were kinetically monitored by DLS measurement. Under physiological pH conditions, the nanocomplex had a condensed size of ~200 nm in diameter and was stable for 12 hr. B, The PBAE polymer-plasmid nanocomplexes became unstable, rapidly dissociated, and enlarged under lower pH conditions (pH < 7). C, Transmission electron microscopy confirmed the condensed nanocomplexes at pH 7.4 with an average size of ~200 nm in diameter and dissociation of the nanocomplexes at pH 5.0 with an enlarged size ranging from 800 to 1200 nm.