The D2O contrasts displayed distinctive features, in particular in the mid-Q range (0.015-0.05 Å - 1 ), which were used for initial fitting of the data. The resulting parameters were then kept constant whilst varying the SLD of the layers and buffer for data gathered at other contrasts, in order to confirm the validity of the solutions identified. The selection of the SLD values for the complexed brushes was based on the SLD of the pristine PDMAEMA brush, based on previously reported values , and that of nucleic acid materials at pH 7.4 (PBS) . To determine the SLD of the complex generated, considering the variation in binding capacity of PDMAEMA brushes for the different nucleic acid materials studied, the Gmax from SPR results were used to identify the maximum ratio of bases per brush repeat unit that could be expected. This ratio was then converted in SLD ratio, reported in Supplementary Table and subsequently used for the fitting of complexed brushes. This allowed the limitation of the parameter space for the fitting of data in all three contrasts studied (Supplementary Figure and Table ). The solution identified involved minor changes in the overall architecture of the brush, resulting in comparable swollen thicknesses, in agreement with the lack of significant changes observed by in situ ellipsometry (Figure ).