In this paper, the fixing and stretching effect of Ni(phen) 2+ 3 with different concentrations on DNA had been studied by Tapping mode AFM. Under an ambient condition, the high resolution DNA images were obtained, the average height, width and length of well spread DNA molecules were measured. The results showed that because of the variations of ionic concentration, the density and topography of DNA molecules on substrate had a great difference. The AFM and gel electrophoresis results also showed that, under our experimental condition, DNA molecules kept intact, Ni(phen) 2+ 3 did not catalyze the cleavage activity of EcoRI, therefore, Ni(phen) 2+ 3 would be used to make high resolution physical mapping of DNA by AFM.
