Atomic force microscopy of DNA self-assembled on a highly oriented pyrolytic graphite electrode surface

Abstract

Different types of self-assembled DNA networks were obtained and characterized by tapping mode atomic force microscopy (AFM) on highly oriented pyrolytic graphite (HOPG) electrodes. Both native calf thymus DNA and synthetic DNA with specific base sequences were investigated. The freely adsorption of DNA on the surface of HOPG forms two-dimensional networks. The double-stranded DNA molecules may form cross-linking points on double helix chains, forming intermediate attachments. The differences in AFM morphology of these DNA condensations can be related to the intrinsic properties of the DNA, which lead to different interactions with HOPG. Three-dimensional networks were formed on the HOPG under applied electric field. The effects of external electric field on the condensation of calf thymus DNA have been investigated in detail. It led to a proposition that the DNA molecules may be polarized in the electric field, and attached to the HOPG surface via its one end with the phosphate backbone lying or standing on the substrate depending on the applied potential. The AFM morphological changes of DNA in the presence of external electric field provided insight into DNA interactions.