In Situ Electrochemical Distance Tunneling Spectroscopy of ds-DNA Molecules

The electrical conductance of ds-DNA duplexes containing 8−14 base pairs modified at both ends with a −(CH2)6−SH linker was measured in a buffered aqueous solution using electrochemically controlled distance tunneling spectroscopy. The tunneling experiment with self-complementary 5‘-(GC)n-3‘-(CH2)6−SH (n = 4−7) duplexes attached covalently to a gold STM tip and a Au(111) electrode shows a wide distribution of currents independent of the ds-DNA length. The voltage-induced horizontal orientation of ds-DNA within the junction results in decreased electrical conductance. The lower currents are also observed for ds-DNA molecules containing a single CA base mismatch.