Electronic Signatures of all Four DNA Nucleosides in a Tunneling Gap

Nucleosides diffusing through a 2 nm electron-tunneling junction generate current spikes of sub-millisecond duration
with a broad distribution of peak currents. This distribution narrows 10-fold when one of the electrodes is functionalized with a reagent
that traps nucleosides in a specific orientation with hydrogen bonds. Functionalizing the second electrode reduces contact resistance
to the nucleosides, allowing them to be identified via their peak currents according to deoxyadenosine > deoxycytidine >
deoxyguanosine > thymidine, in agreement with the order predicted by a density functional calculation.