Simple STM Tip Functionalization for Rapid DNA Sequencing: An Ab Initio Green’s Function Study

An ab initio nonequilibrium Green's function study of the electron-transport properties of the adenine, thymine, cytosine, and guanine DNA bases located between gold electrodes has been performed. One-electron transmission spectra were calculated for both gold and sulfur-modified gold electrodes, which are model conditions of scanning tunneling microscopy (STM) experiments with the different tips. It is shown that the nature of chemical bonding between molecules and metal electrodes plays the most significant role in the overall conductance of the systems. The distance between electrodes and the size of molecules are less important, at least when both sides of the molecule form chemical contact with the electrodes. On the basis of the obtained results, a simple two-pass DNA sequencing scheme is suggested.