The results reported in this study shed a new light on nucleic acid complexation by polyelectrolytes and the impact of the resulting architectures for gene delivery. Indeed, the significant impact of the molecular structure of the nucleic acid materials to be delivered, together with that of the brush architecture (as previously studied ), on the surface density and affinity constant of the complex formation not only has implication for the maintenance of the complexes during transport to targeted cells, as well as for the timely release of these cargos upon internalisation. In addition, the deep infiltration of oligos may provide ideal shielding environment and protection from RNAses and enzymatic degradation, but the partial infiltration of mRNA and plasmid DNA could potentially lead to exposure of some of the partially buried residues. Therefore, this work indicates that design of the brush architecture will likely be required in order to allow the optimisation of nucleic acid delivery, depending on the type of molecules to be shuttled.