Examination of the SLD profiles corresponding to these data, prior to and after complexation with different RNA macromolecules, indicated a deep infiltration in all three cases, including with mRNA molecules (Figures and). Indeed, the SLD of the complexes increased significantly, close to the substrate surface, in comparison to the SLD profile of the pristine brushes. This was less pronounced at 3 µg/mL in the case of mRNA, but already very clear for dsRNA 20 bp oligonucleotides. In addition, whereas modest changes in SLD were observed in upper layers of the brush in the case of dsRNA and ssRNA, mRNA adsorption led to significant increase in the SLD profile in the upper layer of the corresponding complex (Figures 5B compared to 5D and F). mRNA complexation was also the only RNA material that led to a slight increase in upper brush swelling. This behaviour suggests that, whereas RNA oligonucleotides infiltrate rapidly deeply within the brush, large mRNA macromolecules display more restricted infiltration profiles and remain at least partly complexed in the upper layers of the brush, perhaps even slightly protruding from the brush. A schematic representation of brush infiltration depicting these possible scenarios is presented in Figures and.