High density thick PDMAEMA brushes (s of 0.5 chains/nm 2 ; h of 30 nm) incubated with 20 bp RNA oligos were found to result in complexes with very comparable thickness to uncomplexed pristine brushes (Figure -B and Table ). The overall thickness of the complex decreased slightly (3-4 nm), whilst the SLD increased more prominently, indicating that complexation of this brush is associated with increased in polymer density, in agreement with previously reported surface plasmon resonance data. However, in our model, we assumed an unaltered SLD for resulting complexes, as precise SLD values are unknown, which resulted in increased apparent water contents for all layers, apart from the uppermost (Table ). Nonetheless, the homogenous shift in SLD throughout the brush thickness indicated a relatively deep infiltration of RNA oligos within the brush. Similar observations were made in the case of thinner yet dense PDMAEMA brushes (s of 0.5 chains/nm 2 ; h of 10 nm, Figure ). The overall SLD of the brush increased throughout, reflecting an increase in density upon complexation, with comparable shifts, in agreement with the notion that RNA oligos can infiltrate within thin or thick PDMAEMA brushes. However, whereas the overall thickness of the brush decreased slightly, the bulk of the brush (layers displaying <95%