A total of 2 μL of jetPEI per μg of DNA was used as a control, following a protocol recommended by the manufacturer, with minor changes to conditions for optimization of transfection efficiencies (DNA concentration, cell density, time of incubation) with our cell culture system. For transfection with polymer brushes, 1 μg of DNA, 2 μL of jetPEI reagent and PDMAEMA-g-SiO2 at N/P ratios 5:1, 10:1, and 15:1 were diluted in 50 μL of 150 mM NaCl solution separately. A total of 50 μL of the resulting cationic polymer solution was then added to the 50 μL of DNA solution (adding in the reversed order can reduce transfection efficiency), the resulting solution was mixed gently and then incubated for 15 to 30 min at room temperature. A total of 100 μL of the cationic polymer/ DNA mix was then added dropwise to each well containing the cells seeded on the previous day (density: 25k) in 1 mL of KSFM and gently mixed by moving the plate side-to-side. The complexes were incubated with the cells for 4 h then the medium was replaced with KSFM with supplements.

Polymer brush-functionalized nanomaterials offer interesting features for the design of gene delivery vectors as their physicochemical and structural properties can be designed independently of the chemistry, size and shape of the nanomaterial core. However, little is known of the parameters regulating the adsorption and infiltration of DNA molecules at the surface of positively charged polymer brushes, despite the importance of such processes for gene delivery. Here we investigate the role of the molecular environment (e.g., pH, type of buffer, concentration) on the interactions between plasmid DNA and positively charged poly(dimethylaminoethyl methacrylate) (PDMAEMA) brushes using a combination of light scattering, electrophoretic light scattering, in situ ellipsometry, and surface plasmon resonance. We show that the conformation of swollen PDMAEMA brushes is modulated by the surrounding buffer and that this impacts strongly on the ability of such brushes and nanomaterials based on these coatings to complex DNA molecules. In turn, the levels of transfection efficiency measured correlate with changes in brush conformation and DNA binding. Therefore, this work demonstrates the importance of molecular design of polymer brushes to control DNA complexation and release in order to optimize the performance of polymer brush-functionalized nanomaterials for gene delivery applications.