  We review recent advances in the DNA sequencing based on the measurement of
transverse electrical currents. Device configurations proposed in the
literature are classified according to whether the molecular fingerprints
appear as the major (Mode I) or perturbing (Mode II) current signals. Scanning
tunneling microscope and tunneling electrode gap configurations belong to the
former category, while the nanochannels with or without an embedded nanopore
belong to the latter. The molecular sensing mechanisms of Modes I and II
roughly correspond to the electron tunneling and electrochemical gating,
respectively. Special emphasis will be given on the computer simulation
studies, which have been playing a critical role in the initiation and
development of the field. We also highlight low-dimensional nanomaterials such
as carbon nanotubes, graphene, and graphene nanoribbons that allow the novel
Mode II approach. Finally, several issues in previous computational studies are
discussed, which points to future research directions toward more reliable
simulation of electrical current DNA sequencing devices.
