The pBAE-CRHR-Zw complexes with reporter pGFP showed hydrodynamic diameter of 250 nm, slightly larger than the 175 nm of pBAE-CRHR/pGFP complexes without Zw (Figure ). This increase in size may be partly due to the zwitterionic moieties and the structured water hydration shell formed around them. As expected, due to the shielding effect of zwitterionic coating, a substantial drop in Z-potential was observed (Figure ). However, the encapsulation capacity of pBAE-CRHR-Zw/pGFP complexes was fully preserved as shown by the gel retardation assay (Figure ). Given the anti-fouling properties of the zwitterionic polymer, a 25 to 50 -fold decrease in transfection efficiency of pBAE-CRHR-Zw/pGFP complexes in HeLa cells (Figure )