The swelling behavior and changes in thickness of PDMAEMA brushes upon exposure to different buffers and complexation with nucleic acid materials was investigated by ellipsometry. The initial dry thickness of polymer brush substrates was first recorded. Subsequently, substrates were left to equilibrate for 10 min in deionised H2O, PBS (pH 7.4) and NaCl 150 mM (pH 7.4) to determine corresponding swollen thicknesses (ℎ !"#$$%& ). Substrates were then removed from the liquid cell and nucleic acid materials solutions (3 ug/mL) were promptly injected over the substrate surface dropwise (about 150 uL). Complexation was left to proceed for 10 min. Upon complexation, substrates were washed with buffer and placed in the liquid cell to determine the final swollen thickness of the complex. Finally, substrates were washed with abundant water and ethanol and dried for determination of the change in dry thickness. Changes in both dry and swollen thicknesses were presented as percentage relative to the initial corresponding thickness. All measurements were carried out in triplicates using substrates from separate polymerisation solutions.