A DNA diode

It looks as if this week will become my "what-else-is-happening-in-DNA-research" week. Yesterday the alternate use of stop codons in some bacteria and today the fascinating research by colleagues from the US and Israel - a nanoscale diode made out of DNA.

Continuous demand for more computing power is pushing the limitations of present day methods. This need is driving researchers to look for molecules with promising properties and find ways to establish reliable contacts between molecular components and bulk materials in an electrode, in order to mimic conventional electronic elements at the molecular scale.

An example for such an element is the nanoscale diode (or molecular rectifier). A diode operates like a valve to facilitate electronic current flow in one direction. Researchers envision that a collection of these nanoscale diodes, that are essentially molecules, has properties that resemble traditional electronic components such as a wire, transistor or rectifier. The emerging field of single molecule electronics hopes to find ways to overcome Moore's Law - the observation that over the history of computing hardware the number of transistors in a dense integrated circuit has doubled approximately every two years - beyond the limits of conventional silicon integrated circuits.

The researchers took a single DNA molecule constructed from just 11 base pairs and connected it to an electronic circuit only a few nanometers in size. When they measured the current through the molecule, it did not show any special behavior. However, when layers of a coralyne were inserted between layers of DNA, the behavior of the circuit changed drastically. Coralyne is a small crescent-shaped molecule that is among a group of molecules known to preferentially intercalate DNA triplexes over duplexes and to increase the thermal stability of triplex DNA . In the case of the diode experiment the current jumped to 15 times larger negative vs. positive voltages--a necessary feature for a nano diode.

In summary, we have constructed a molecular rectifier based on intercalating specific, small molecules into designed DNA strands. Not only do these results offer a new method for studying the DNA–molecule interaction, they also suggest a novel strategy for engineering molecular electronic elements based on a specifically designed functional DNA complex.