Naked DNA Helicity Observed by Scanning Tunneling Microscopy

Uncoated DNA molecules marked with an activated Tris 1-Aziridinyl Phosphine Oxide (TAPO) solution were deposited on gold substrates and imaged in air with high resolution Scanning Tunneling Microscope (STM). Constant current and barrier height STM images show a clear evidence of the helicity of the DNA structure: pitch periodicity ranges between 25 and 34 Å while the average diameter is 20 Å. Molecular structure within a single helix turn is also observed.