The samples were studied with a scanning electron microscope(Merlin FEG-SEM, Zeiss, Germany) after they were sputtered withAu/Pd to avoid charging. The atomic force microscopy images wereacquired on the DNA-immobilized samples in air with Dimension Icon (Bruker, Germany) instrument, equipped with ScanAsyst-Air probes. The sample was mounted on a magnetic holder using adouble adhesive tape, and the images were acquired in the peakforce tapping mode.