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Nanomachinery lights up


25 February 2010

A light-activated switch to turn nanomachines on and off has been developed by Japanese researchers. The team showed how tiny tweezers made with DNA could be triggered to open and close in response to UV and visible light. The clever mechanism is hoped to find useful roles in designing future nano-robots. 

DNA is a versatile building block to construct nanomachinery that is small enough to interact with single molecules. But these nanomachines usually require a source of 'fuel' to trigger activity: typically small DNA fragments that are added each cycle. The problems associated with this process are delays in activating and deactivating systems, and the build up of waste products that can inhibit movement.  

'We are designing DNA nano-robotics that are mechanically operated by light rather than chemical fuel,' says Hiroyuki Asanuma, who led the research at Nagoya University, Japan. 'In other words, we are creating "environment-friendly" nano-robotics.' 

The team focused their work on a loop of DNA that resembles a hairpin with two arms. At the end of each arm, azobenzene groups are integrated into the DNA sequence. Under visible light, the azobenzene groups adopt the trans isomer - rather like outstretched fingers - allowing the base pairs to join together and interlock.  

When UV light is applied, the azobenzene groups switch to the more sterically-constrained cis isomer, as if the fingers were curled up. This no longer favours the arms being joined together, so the strands come apart and the loop falls open. Once open, the DNA strand that was trapped in the hairpin can undergo reactions, and is effectively 'turned on'. 

Light-driven DNA nanomachine

Azobenzene moieties act as photoswitches, taking the trans form under visible light and the cis form under UV light

© Angew. Chem. Int. Ed.

Alexander Heckel at Goethe University in Frankfurt, Germany, is impressed by the work. 'In designing nanomachines it is very important to be able to form interactions and break them again. Light is not only a waste-free approach, but can also be applied with spatiotemporal control,' he says. 

Since the system is fully reversible and simple, it has great potential to be applied to other nanotechnology that uses DNA. 'To be able to switch biomolecular conformational changes is of considerable interest for many applications in biomedicine and bionanotechnology,' says Friedrich Simmel, who designs nanomachines at the Technical University of Munich, Germany.  

'Photoswitching offers a convenient way to control such processes "from outside". For example, the strategy developed here could use light to trigger RNA degradation in vivo or control the movement of nanoscale systems,' he adds. 

Lewis Brindley 

 

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References

M Zhou et al, Angew. Chem. int. Ed., 2010, DOI: 10.1002/anie.200907082

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