Humidity Effects on Imaging and Nanomanipulation of Individual DNA Molecules on HOPG Surface

Single DNA molecules are aligned on highly ordered pyrolytic graphite (HOPG) surface in ambient air. It is shown that environmental humidity has a remarkable influence on the measured height of DNA by atomic force microscopy (AFM), probably due to the conformation transition of DNA. We also demonstrate that DNA molecules deposited on HOPG surfacecan be `pushed' much more easily by AFM tip at high humidity than at low one.