11 november 2013

All aboard the nanotrain network

Science

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Tiny self-assembling transport networks, powered by nano-scale motors and controlled by DNA, have been developed by scientists at Oxford University and Warwick University.

The system can construct its own network of tracks spanning tens of micrometres in length, transport cargo across the network and even dismantle the tracks.

The work is published in Nature Nanotechnology and was supported by the Engineering and Physical Sciences Research Council and the Biotechnology and Biological Sciences Research Council.

Researchers were inspired by the melanophore, used by fish cells to control their colour. Tracks in the network all come from a central point, like the spokes of a bicycle wheel. Motor proteins transport pigment around the network, either concentrating it in the centre or spreading it throughout the network. Concentrating pigment in the centre makes the cells lighter, as the surrounding space is left empty and transparent.

The system developed by the Oxford University team is very similar, and is built from DNA and a motor protein called kinesin. Powered by ATP fuel, kinesins move along the micro-tracks carrying control modules made from short strands of DNA. 'Assembler' nanobots are made with two kinesin proteins, allowing them to move tracks around to assemble the network, whereas the 'shuttles' only need one kinesin protein to travel along the tracks.

Green dye-carrying shuttles sit idle on the tracks before refuelling

'DNA is an excellent building block for constructing synthetic molecular systems, as we can program it to do whatever we need,' said Adam Wollman, who conducted the research at Oxford University's Department of Physics. 'We design the chemical structures of the DNA strands to control how they interact with each other. The shuttles can be used to either carry cargo or deliver signals to tell other shuttles what to do.

'We first use assemblers to arrange the track into 'spokes', triggered by the introduction of ATP. We then send in shuttles with fluorescent green cargo which spread out across the track, covering it evenly. When we add more ATP, the shuttles all cluster in the centre of the track where the spokes meet. Next, we send signal shuttles along the tracks to tell the cargo-carrying shuttles to release the fluorescent cargo into the environment, where it disperses. We can also send shuttles programmed with 'dismantle' signals to the central hub, telling the tracks to break up.'

This demonstration used fluorescent green dyes as cargo, but the same methods could be applied to other compounds. As well as colour changes, spoke-like track systems could be used to speed up chemical reactions by bringing the necessary compounds together at the central hub. More broadly, using DNA to control motor proteins could enable the development of more sophisticated self-assembling systems for a wide variety of applications.

Video: The time-lapse video shows the network, with tracks shown in red, handling a cargo of fluorescent green dye over a period of eight minutes. There's a flash of bright green when the dye-carrying nanoshuttles are first added, which soon find their way onto the tracks. The shuttles are given ATP fuel at 209 seconds in, powering their journey to the centre of the network. Once they reach the centre at 319s, clean-up shuttles with the 'release' signal are sent in. These remove the dye from the network, leaving the tracks empty but for a few stragglers.

The time is shown in seconds (top left) and the scale bar is 10 micrometres (bottom left).