Direct current electrical characterization of ds-DNA in nanogap junctions

Samir Muzaffar Iqbal, Birck Nanotechnology Center and School of Electrical and Computer Engineering, Purdue University,
G. Balasundaram, Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University
Subhasis Ghosh, School of Physical Sciences, Jawaharlal Nehru University
Donald E. Bergstrom, Birck Nanotechnology Center and Bindley Bioscience Center, Purdue University
Rashid Bashir, Birck Nanotechnology Center and Bindley Bioscience Center, Purdue University

Abstract

Measurements of DNA conductivity, hybridization, and melting using electronic means can have wide applications in molecular electronics and biological sensors. We have fabricated nanogap break-junctions by electromigration through thin gold-on-titanium films. 18-mer thiolated ds-DNA molecules were covalently attached between the electrodes and dc electrical measurements were done. The conductance was measured through the molecule before and after a temperature ramp from 300 to 400 K. A dramatic decrease in conductance was observed, analogous to an electrical fuse, possibly attributed to complete or partial denaturing of the ds-DNA molecules bridging the nanogaps. We also show evidence that the dc resistance of dry DNA strands of the same length decreases with increasing guanine-cytosine content in the sequence with values ranging from 10 M ! to 2 G !. These findings can have important consequences in DNA-based molecular