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.