A train-like system that transports molecular cargo between specific pick-up and delivery zones on a chip has been created by Swiss scientists. The technology could lead to nanoscale assembly lines, or improved self-healing materials, they claim. 

Developing systems that use nanomotors to move molecular cargos around inside nanoscale devices has become popular recently. As unlike random diffusion, cargo can be moved against a concentration gradient and in contrast to microfluidic devices, an external electrical supply or pump isn't needed for the transportation.

Now, Claudia Schmidt and Viola Vogel based at Swiss Federal Institute Zürich (ETH Zürich) have - for the first time - successfully integrated separate pick-up and delivery zones into one system. The team already had a working system where a microtubule is propelled along a carpet of motor proteins inside a chip: the 'train' and 'train track'. To improve their system, Schmidt and Vogel have added 'departure and arrival stations'.

 

Cargo is picked up and delivered using DNA strands

The researchers labelled the cargo with stretches of DNA, and placced complementary strands on the pick-up and delivery stations. By tuning the length of the DNA strands on the stations, and the geometry of the interactions, the team could control the strength of the different interactions and crucially the force needed to break them. Tailoring the force required to rupture the bonds ensures the cargo is collected at the pick-up station and deposited at the delivery station. The relative strengths of the interactions means that the cargo cannot be collected at the delivery station - so it doesn't make the reverse trip.

'Recreating the intracellular transport systems, where motor proteins deliver packages like FedEx couriers, in a synthetic environment has been a goal in nanotechnology for the past decade,' says Henry Hess, an expert in biomedical engineering at Columbia University, New York, US. 'The work is remarkable for harnessing diverse concepts and approaches - including DNA nanotechnology, microfabrication, self-assembly and molecular motors - to realise a complex nanoscale process,' he adds. 

In the future, Schmidt says that the team hope to develop a nanoscale assembly line and eventually 'integrate their transport system into synthetic self-healing materials that mimic wound-healing'.

Russell Johnson 

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