Distinct mechanisms of DNA sensing based on N-doped carbon nanotubes with enhanced conductance and chemical selectivity.

N-doped capped carbon nanotube (CNT) electrodes applied to DNA sequencing are studied by first-principles calculations. For the face-on nucleobase junction configurations, a conventional conductance ordering is obtained where the largest signal results from guanine according to its high highest occupied molecular orbital (HOMO) level, whereas for the edge-on counterparts a distinct conductance ordering is observed where the low-HOMO thymine provides the largest signal. The edge-on mode is shown to operate based on a novel molecular sensing mechanism that reflects the chemical connectivity between N-doped CNT caps that can act both as electron donors and electron acceptors and DNA functional groups that include the hyperconjugated thymine methyl group.