Topographic characterization and electrostatic response of M-DNA studied by atomic force microscopy

Modified DNA species have attracted the interest of the scientific community in the last years in a search for an appropriate molecular wire for the incoming nanotechnology. M-DNA, a complex of DNA with divalent metallic ions, is one of the candidates for a molecular wire. In this paper we describe the procedure to fabricate M-DNA using NiCl2 and CoCl2, and a simple test to check the production of the modified biomolecule. We present atomic force microscope (AFM) images of nickel and cobalt M-DNA. Our results show that the DNA modified with these metal ions suffers a fivefold reduction in length and an increment of almost one order of magnitude in height as compared to the length and height of regular B-DNA. This type of condensation of the DNA is fully reversible upon the addition of EDTA. AFM images of reversed M-DNA show no differences from regular B-DNA. Two types of electrostatic experiment performed on this modified molecule show no evidence for metallic or semiconductor behaviour.