Sep 25, 2021

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Everybody knows that wires conduct electrical currents and that molecules of DNA determine heredity through genetic data. But did you know that DNA itself can conduct electrical currents? 

This flow discovered in recent years by scientists who thought that characteristic makes the double helix of two polynucleotide chains a potential  candidate for roles that nature did not intend for it — including smaller, faster and cheaper electric circuits in electronic devices and to detect the early stages of diseases like cancer and COVID-19.

In a study recently published as a letter in the prestigious journal Nature Nanotechnology under the title “Backbone charge transport in double-stranded DNA,”  Hebrew University of Jerusalem Prof. Danny Porath and his team at its Institute of Chemistry and the Center for Nanoscience and Nanotechnology have helped advance the development of such applications by showing a highly-reliable method to measure electric currents that pass through a DNA molecule. 

Porath’s study was carried out in conjunction with Alexander Kotlyar at Tel Aviv University, the late Yossi Sperling from the Weizmann Institute of Science in Rehovot and researchers from Cyprus, Spain, the US and India.

They were able to locate and identify individual molecules between the electrodes and measure significant electric currents in individual DNA molecules.  Their most surprising finding was that the current passes through the DNA backbone, contrary to prior assumptions in the scientific community that the current flowed along DNA base-pairs.  “Our method’s high degree of reliability, experimental reproducibility and stability allows for a wide range of experiments, in which researchers may learn about the conduction properties of DNA and bring the field closer to creating DNA-based medical detectors and electronic circuits,” explained Porath.

Doctoral student Roman Zhuravel of the HU team overcame long-held technical difficulties to develop a technique that could reliably attach a single DNA molecule to electric contacts.  To verify that most of the current passes through the backbone, he created discontinuities in the backbone itself—on both sides of the double-helix—and saw that, in this case. there was no current.

“Understanding charge transport in DNA molecules is a long-standing problem of fundamental importance across disciplines. It is also of great technological interest due to DNA’s ability to form versatile and complex programmable structures. Charge transport in DNA-based junctions has been reported using a wide variety of set-ups, but experiments so far have yielded seemingly contradictory results that range from insulating or semiconducting to metallic-like behavior,” they wrote. 

“As a result, the intrinsic charge transport mechanism in molecular junction set-ups is not well understood, which is mainly due to the lack of techniques to form reproducible and stable contacts with individual long DNA molecules. Here we report charge-transport measurements through single 30-nm-long double-stranded DNA molecules with an experimental set-up that enables us to address individual molecules repeatedly and to measure the current–voltage characteristics from 5 Kelvin up to room temperature. Strikingly, we observed very high currents of tens of nanoamperes, which flowed through both homogeneous and non-homogeneous base-pair sequences. The currents are fairly temperature-independent in the range 5 to 60 K and show a power-law decrease with temperature above 60 K, which is reminiscent of charge transport in organic crystals.” 

For Porath, these findings are a highlight of his career. “We were able to debunk a 20-year-old paradigm. While many technical hurdles still need to be worked out, we’ve taken a big step forward toward the holy grail of building a DNA-based electronic circuit.”