Will this DNA molecular switch replace conventional transistors?

December 14, 2015

A model of one form of double-stranded DNA attached to two electrodes (credit: UC Davis)

What do you call a DNA molecule that changes between high and low electrical conductance (amount of current flow)?

Answer: a molecular switch (transistor) for nanoscale computing. That’s what a team of researchers from the University of California, Davis and the University of Washington have documented in a paper published in Nature Communications Dec. 9.

“As electronics get smaller they are becoming more difficult and expensive to manufacture, but DNA-based devices could be designed from the bottom-up using directed self-assembly techniques such as ‘DNA origami’,” said Josh Hihath, assistant professor of electrical and computer engineering at UC Davis and senior author on the paper.

DNA origami is the folding of DNA to create two- and three-dimensional shapes at the nanoscale level (see DNA origami articles on KurzweilAI).

Hihath suggests that DNA-based devices may also improve the energy efficiency of electronic circuits, compared to traditional transistors, where power density on-chip has increased as transistors have become miniaturized, limiting further miniaturization.

This illustration shows double-stranded DNA in two configurations, B-form (blue) and A-form (green), bound to gold electrodes (yellow). The linkers to the electrodes (either amines or thiols) are shown in orange. (credit: Juan Manuel Artés et al./Nature Communications)

To develop DNA into a reversible switch, the scientists focused on switching between two stable conformations of DNA, known as the A-form and the B-form. In DNA, the B-form is the conventional DNA duplex molecule. The A-form is a more compact version with different spacing and tilting between the base pairs. Exposure to ethanol forces the DNA into the A-form conformation, resulting in increased conductance. Removing the ethanol causes the DNA to switch back to the B-form and return to its original reduced conductance value.

But the authors advise that to develop this finding into a technologically viable platform for electronics will require a great deal of work to overcome two major hurdles: billions of active DNA molecular devices must be integrated into the same circuit, as is done currently in conventional electronics; and scientists must be able to gate specific devices individually in such a large system.

Abstract of Conformational gating of DNA conductance

DNA is a promising molecule for applications in molecular electronics because of its unique electronic and self-assembly properties. Here we report that the conductance of DNA duplexes increases by approximately one order of magnitude when its conformation is changed from the B-form to the A-form. This large conductance increase is fully reversible, and by controlling the chemical environment, the conductance can be repeatedly switched between the two values. The conductance of the two conformations displays weak length dependencies, as is expected for guanine-rich sequences, and can be fit with a coherence-corrected hopping model. These results are supported by ab initio electronic structure calculations that indicate that the highest occupied molecular orbital is more disperse in the A-form DNA case. These results demonstrate that DNA can behave as a promising molecular switch for molecular electronics applications and also provide additional insights into the huge dispersion of DNA conductance values found in the literature.