Novel DNA circuits may lead to gen-next bio devices

Scientists have created stable DNA circuits that can more efficiently transport charge, paving the way for a new generation of bio-devices. The DNA circuits created by researchers at Arizona State University (ASU) and Duke University in the US is capable of splitting and combining current, much like an adapter that can connect multiple appliances to a wall outlet. "The ability of DNA to transport electrical charge has been under investigation for some time," said Nongjian Tao, from ASU.

"Splitting and recombining current is a basic property of conventional electronic circuits. We'd like to mimic this ability in DNA, but until now, this has been quite challenging," Tao said. Current splitting in DNA structures with three or more terminals is difficult as charge tends to rapidly dissipate at splitting junctions or convergence points. In the study published in the journal Nature Nanotechnology, a special form, known as G-quadruplex (G4) DNA is used to improve charge transport properties. G4 DNA is composed of four rather than two strands of DNA that are rich in the nucleotide guanine.

"DNA is capable of conducting charge, but to be useful for nanoelectronics, it must be able to direct charge along more than one path by splitting or combining it," said Peng Zhang, an assistant research professor at Duke University. "We have solved this problem by using the guanine quadruplex (G4) in which a charge can arrive on a duplex on one side of this unit and go out either of two duplexes on the other side" said Zhang.

"This is the first step needed to transport charge through a branching structure made exclusively of DNA. It is likely that further steps will result in successful DNA-based nanoelectronics that include transistor-like devices in self-assembling 'pre-programmed' materials," he said. DNA is a highly attractive material for the design and creation of new nanoelectronics. The molecule's four nucleotide bases labelled A,T,C and G can be programmed to self-assemble into iconic double-helices. 

However the molecule can also assemble to form G4 DNA. Naturally-occurring guanine-rich quadruplex DNA serves a number of important physiological functions. In G4 structures, DNA takes the form of stacked guanine bases that form hydrogen bonds with their two immediate neighbours. The G4 structure at the heart of the new experiments, with its improved properties of charge transport, allowed researchers, for the first time, to design effective conducting pathways between the stacked G-quadruplex DNA and the double-stranded wires that form the terminals for either splitting or merging electrical current flow.

Earlier efforts to create such a Y-shaped electrical junction using only conventional double-stranded DNA had failed, due to the very poor charge transport properties inherent in the circuit's junction points.
Using G4 DNA as a connector element in multi-ended DNA junctions was shown to dramatically improve charge transport through both three and four terminal DNA circuits.