Direct conductance measurement of single DNA molecules in aqueous solution

We have studied electron transport in DNA duplexes, covalently bonded to two electrodes in aqueous buffer solutions, by repeatedly forming a large number of DNA junctions. The histogram of conductances reveals peaks at integer multiples of a fundamental value, which is used to identify with the conductance of a single DNA molecule. The measured conductance depends on the DNA sequence and length. For (GC)_n sequences, the conductance is inversely proportional to the length (greater than eight base pairs). When inserting (A:T)_m into GC-rich domains, it decreases exponentially with the length of A:T base pairs (m) with a decay constant of 0.43 Å^-1. This work provides an unambiguous determination of single DNA conductance and demonstrates different conduction mechanisms for different sequences.