TDAB-induced DNA plasmid condensation on the surface of a reconstructed boron doped silicon substrate

Our study aims at a better control and understanding of the transfer of a complex [DNA supercoiled plasmid – dodecyltrimethylammonium surfactant] layer from a liquid–vapour water interface onto a silicon surface without any additional cross-linker. The production of the complexed layer and its transfer from the aqueous subphase to the substrate is achieved with a Langmuir–Blodgett device. The substrate consists of a reconstructed boron doped silicon substrate with a nanometer-scale roughness. Using X-ray photoelectron spectroscopy and atomic force microscopy measurements, it is shown that the DNA complexes are stretched in a disorderly manner throughout a 2–4 nm high net-like structure. This architecture is composed of tilted cationic surfactant molecules bound electrostatically to DNA, which exhibits a characteristic network arrangement with a measured average fiber diameter of about 45 ± 15 nm covering the entire surface. The mechanism of transfer of this layer onto the planar surface of the semi-conductor and the parameters of the process are analysed and illustrated by atomic force microscopy snapshots. The molecular layer exhibits the typical characteristics of a spinodal decomposition pattern or dewetting features. Plasmid molecules appear like long flattened fibers covering the surface, forming holes of various shapes and areas. The cluster–cluster aggregation of the complex structure gets very much denser on the substrate edge. The supercoiled DNA plasmids undergo conformational changes and a high degree of condensation and aggregation is observed. Perspectives and potential applications are considered.