Scanning tunnelling microscopy imaging of the DNA base molecules on reduced SrTiO3(100) surfaces

The four DNA bases, adenine, guanine, thymine and cytosine, have been deposited on a reduced SrTiO3(100) substrate and been observed by scanning tunnelling microscopy (STM) in ultrahigh vacuum (UHV) conditions. The images indicate that the bases are deposited as individual molecules in UHV conditions, and can be individually observed by STM. The lateral dimensions of adenine and guanine are 1.5−1.0 nm and of thymine and cytosine are 1.0−0.6 nm with a sample bias voltage from −1 to −3 V. It has been revealed that a comparison of the heights and lateral dimensions of the deposited species, and also of the bias dependence of the heights, allows differentiation between the four DNA bases in real space.