Neutron reflecometry provided some of the contrast and resolution required to probe associated changes in brush morphology upon complexation. In agreement with ellipsometry data, the swelling of brushes was not found to change significantly, although hydration levels increased in deeper layers of PDMAEMA brushes. Interestingly, all nucleic acid materials, at least upon exposure at high concentrations, were found to reach inner layers of the brush. However, in the case of mRNA and pDNA, partial infiltration was observed and more significant changes in upper brush layers were observed. These results suggest that the reduced surface densities achieved for 20 bp dsDNA oligos are not associated with a poorer penetration, but simply reflect weaker packing, perhaps due to the lack of hydrogen bonding interactions with tertiary ammine and ammonium residues. In contrast, the reduced binding of larger nucleic acid materials seems to be directly linked to more restricted conformational freedom and the lack of full infiltration of their structure, perhaps preventing the further adsorption of additional molecules.