The effect of underlying octadecylamine monolayer on the DNA conformation on the graphite surface.

DNA was immobilized on highly oriented pyrolytic graphite (HOPG) surfaces modified in octadecylamine (ODA) vapor. ODA molecules, deposited from the vapor phase onto HOPG form a nanostructured surface, which was utilized as a template for DNA adsorption. Peculiarities of double- and single-stranded DNA adsorption on these surfaces were investigated with atomic force microscopy (AFM) both in air, liquid and under different salt conditions. AFM images of DNA molecules immobilized on octadecylamine modified HOPG reveal a segmented shape of biopolymers: it constitutes straight segments with sharp turns at angles 120 degrees or 60 degrees between them, reflecting the symmetry of the underlying pattern. The analysis of DNA conformations on ODA modified HOPG surface has shown that under certain conditions DNA equilibrates on the surface on the scale of the whole molecule. A persistence length estimate of 97nm was determined for those molecules. Participation of different forces in the ODA pattern driven DNA assembly is discussed.