19th December 2013

DNA motor 'walks' along nanotube, transports tiny particle

Researchers have created a new type of molecular motor made of DNA and used it to transport a nanoparticle along the length of a carbon nanotube.

This design was inspired by natural biological motors that evolved to perform specific tasks vital to the function of cells – according to Jong Choi, assistant professor of mechanical engineering at Purdue University.

Whereas biological motors are made of protein, researchers are working towards creating synthetic motors based on DNA, the genetic materials in cells that consist of four chemical bases in a sequence: adenine, guanine, cytosine and thymine. The walking mechanism of synthetic motors is far slower than the mobility of natural motors. However, natural motors cannot be controlled, and they don't function outside their natural environment, whereas DNA-based motors are more stable and could be switched on and off.

"We are in the very early stages of developing these kinds of synthetic molecular motors," Choi said.

In future decades, such devices may be used in drug delivery, manufacturing and chemical processing at the nanoscale – perhaps forming the components and moving parts of tiny robots. His team's latest findings are published in the journal Nature Nanotechnology.

The motor has a core, with two arms made of DNA above and below the core. As it moves along a carbon-nanotube track it harvests energy from strands of RNA, molecules vital in living cells and viruses.

"Our motors extract chemical energy from RNA molecules decorated on the nanotubes and use that energy to fuel autonomous walking along the carbon nanotube track," Choi explained.

The core is made of an enzyme that cleaves off part of an RNA strand. After cleavage the upper DNA arm moves forward, binding with the next strand of RNA, and then the rest of the DNA follows. The process repeats until reaching the end of the nanotube track.

The team used this motor to move nanoparticles of cadmium disulfide along the length of a nanotube. Each nanoparticle (pictured yellow) was just 4 nanometres in diameter. For comparison, a red blood cell is about 7,000 nanometres.

To record the motor's movement, the team combined two fluorescent imaging systems – one in the visible light spectrum and the other in near-infrared. The nanoparticle was fluorescent in visible light and the nanotubes were fluorescent in the near-infrared. The motor took about 20 hours to reach the end of the nanotube, which was several microns long, but the process could be accelerated by changing pH (a measure of acidity) and temperature.

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