The world's smallest diode

US and Israeli researchers have created and characterised the world’s smallest diode — one molecule small, to be precise. The achievement was led by Professor Bingqian Xu from the University of Georgia (UGA) and Dr Yoni Dubi from Ben-Gurion University (BGU).

A diode is an electronic element that allows current to flow in one direction but prevents its flow in the other direction. It is a central element in electronic devices, such as mobile phones and computers and essentially any electronic appliance.

“For 50 years, we have been able to place more and more computing power onto smaller and smaller chips, but we are now pushing the physical limits of silicon,” said Xu, an associate professor in the UGA College of Engineering. “If silicon-based chips become much smaller, their performance will become unstable and unpredictable.”

To find a solution to this challenge, Xu turned to DNA. He said DNA’s predictability, diversity and programmability make it a leading candidate for the design of functional electronic devices using single molecules.

Xu and his team isolated a specifically designed single-duplex DNA of 11 base pairs and connected it to an electronic circuit only a few nanometres in size. When they measured the current through the molecule, the researchers found that the molecule did not show any special behaviour.

However, when the DNA was intercalated with a molecule called coralyne, the behaviour of the circuit changed drastically — now, the current was 15 times larger for negative voltages than for positive voltages, a necessary feature for a diode. The researchers deduced that they had created a diode composed of a single DNA molecule.

“This finding is quite counterintuitive because the molecular structure is still seemingly symmetrical after coralyne intercalation,” said Xu.

To understand the origin of this feature, Dr Dubi and his student, Elinor Zerah-Harush, used the results of the experiment to construct a theoretical model of the DNA molecule inside the electric circuit. The model allowed them to identify the source of the diode-like feature: it originates from the breaking of spatial symmetry inside the DNA molecule after the coralyne is inserted.

Published in the journal Nature Chemistry, the research has demonstrated for the first time that one can make tiny electronic elements from single DNA molecules. This could lead to progress in the design and construction of nanoscale electronic elements, with Xu suggesting, “Our discovery can lead to progress in the design and construction of nanoscale electronic elements that are at least 1000 times smaller than current components.”

The two teams are continuing the collaboration, with the common goal of constructing more molecular devices and enhancing the performance of the molecular diode.