Improvement of DNA-visualization in dynamic mode atomic force microscopy in air

Near-contact mode atomic force microscopy (AFM) imaging leads to sharper re presentations of DNA double strands on mica imaged at ambient conditions co mpared with noncontact mode AFM. Phase shift was used for feedback control yielding height information using a simple model calculation. No contact be tween tip and sample occurs. Measured DNA widths were up to four times smal ler than measured with the same AFM tip in noncontact mode at ambient condi tion.