Measuring the electrical conductivity through a specific strand of DNA is of great interest to the nano-science and engineering community. This work focuses on the electrical conduction through 15 base-pair, double helix oligo-nucleotides with various sequences. The current-voltage characteristics of the double strands are measured in a metal(Au)/ds-DNA/metal(Au) structure fabricated by immobilizing the dithiol derivatized double-stranded DNA oligionuleotide sequences in nanoscale gaps between pairs of gold (Au) electrodes, achieved through an electromigration-induced break-junction (EIBJ) technique performed at room temperature. The double-stranded DNA configuration was immobilized on the electrodes by assembling the oligonucleotides into the double-helix conformation in an aqueous solution, reacting these solutions with the electrodes in an aqueous solution, locking the double-helix configuration with a polycation, and rinsing with copious amount of ultrapure water to remove any residual salt. In measurements on nominally dry devices, approximately 1G℆ conduction was measured through a sequence of GC rich, 3’ thiol labeled DNA. Replacing a single GC-pair in the center of the sequence with an AT pair results in a conductance decrease of more than one order of magnitude. Negligible conductivity was measured in AT rich or 5’ thiol labeled DNA. This is consistent with single molecule conduction measurements where enhanced conductivity has been observed in GC rich DNA. Higher conductivity is observed for devices immobilized with GC-rich DNA in a higher concentration of salt (NaCl) in the standard phosphate buffer silane (PBS) solution, which is attributed to a larger number of DNA-molecules immobilized between the electrodes. This study demonstrates that EIBJ technique at room temperature can be used to efficiently build hybrid nano-bio inspired devices with symmetric electrodes and useful experiments can be performed to understand the electrical properties in nanometer scale materials such as DNA.
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Purdue University, West Lafayette, IN