In addition to the formation and stability of polyplexes, the size and zeta potential of the polyplex nanoparticles are crucial factors impacting transfection performance. To assess the influence of PEI modification on nanoparticle formation, we determined the resulting PEI polyplex particle size and the zeta potential via dynamic light scattering (Figure ). For transfection we used pGL3 plasmid (4818 bp) but for particle sizing and zeta potential measurements we used pUC19 plasmid (2686 bp). Prior studies, however, have suggested that plasmid size does not play a major role in the physicochemical properties of nonviral DNA complexes. Consistent with subsequent transfection experiments, all PEI-based polyplexes were examined at a polymer/DNA weight ratio of 3, apart from zPEI30, which required a weight ratio of 6 to achieve full condensation.