Much like flipping a light switch at home—only on a scale 1,000 times smaller than a human hair—a team of researchers has now developed the first controllable DNA switch to regulate the flow of electricity within a single, atomic-sized molecule. The new study, led by Arizona State University Biodesign Institute researcher Nongjian Tao, is published in the online journal Nature Communications.
"It has been established that charge transport is possible in DNA, but for a useful device, one wants to be able to turn the charge transport on and off,” said Tao. “We achieved this goal by chemically modifying DNA. Not only that, but we can also adapt the modified DNA as a probe to measure reactions at the single-molecule level. This provides a unique way for studying important reactions implicated in disease, or photosynthesis reactions for novel renewable energy applications."
Previously, Tao's research group had made several discoveries to understand and manipulate DNA to more finely tune the flow of electricity through it. They found they could make DNA behave in different ways—and could cajole electrons to flow like waves according to quantum mechanics, or "hop" like rabbits in the way electricity in a copper wire works—creating an exciting new avenue for DNA-based, nano-electronic applications.
DNA Modification
To accomplish their engineering feat, Tao's group modified just one of DNA's iconic double helix chemical letters (abbreviated as A, C, T or G) with another chemical group, called anthraquinone (Aq). Anthraquinone is a three-ringed carbon structure that can be inserted in between DNA base pairs and contains a redox group.
These chemical groups are the foundation for how our bodies' convert chemical energy through switches that send all of the electrical pulses in our brains and our hearts and communicate signals within every cell that may be implicated in the most prevalent diseases.
Through their studies, when they sandwiched the DNA between a pair of electrodes, they careful controlled their electrical field and measured the ability of the modified DNA to conduct electricity. This was performed using a staple of nano-electronics: a scanning tunneling microscope, which acts like the tip of an electrode to complete a connection, being repeatedly pulled in and out of contact with the DNA molecules in the solution.
"We found the electron transport mechanism in the present anthraquinone-DNA system favors electron "hopping" via anthraquinone and stacked DNA bases," said Tao.
In addition, they found they could reversibly control the conductance states to make the DNA switch on (high-conductance) or switch-off (low conductance). When anthraquinone has gained the most electrons (its most-reduced state), it is far more conductive, and the team finely mapped out a 3D picture to account for how anthraquinone controlled the electrical state of the DNA.
For their next project, they hope to extend their studies to get one step closer toward making DNA nano-devices a reality.
"We are particularly excited that the engineered DNA provides a nice tool to examine redox reaction kinetics, and thermodynamics the single molecule level," said Tao.
For more nanoelectronics news, find out how to build nanoelectronics devices, atom by atom.