Probing electrical properties of oriented DNA by conducting atomic force microscopy

Different methods have been applied for the stretching of DNA molecules on chemically functionalized surfaces by various modified reagents, i.e. 3-ami nopropyltriethanoxysilane or polylysine on mica and 2-mercaptoethylamine on Au(111)/mica by a moving interface technique, magnesium cation (Mg2+) on m ica by a spin-stretching method and DNA on an atomic-level flat mica by a f ree-flowing method. The long lambda -DNA molecule is well elongated using t he moving interface technique. The DNA molecule array density can be contro lled by the change of surface charge density and the DNA concentration. On the other hand, the novel free-flowing method is very useful for the alignm ent of short polynucleotide molecules. Shadow-mask evaporation has been use d to fabricate a gold electrode contacted electrically to the oriented DNA molecules. The intrinsic electrical properties of individual DNA molecules are directly measured using a conducting probe atomic force microscope equi pped with a gold-coated conductive tip. The DNA molecule is considered as a promising molecular wire.