Cars, planes and many electronic products are now built with the help of sophisticated assembly lines. Mobile assembly carriers, on to which the objects are fixed, are an important part of these assembly lines.

In the case of a car body, the assembly components are attached in various work stages arranged in a precise spatial and chronological sequence, resulting in a complete vehicle at the end of the line.

The creation of such an assembly line at molecular level has been a long-held dream of many nanoscientists. "It would enable us to assemble new complex substances or materials for specific applications," says Professor Viola Vogel, head of the Laboratory of Applied Mechanobiology at ETH Zurich.

Vogel has been working on this ambitious project together with her team and has recently made an important step.

In a paper published in the latest issue of the Royal Society of Chemistry's Lab on a Chip journal, the ETH researchers presented a molecular assembly line featuring all the elements of a conventional production line: a mobile assembly carrier, an assembly object, assembly components attached at various assembly stations and a motor (including fuel) for the assembly carrier to transport the object from one assembly station to the next.

Production line three times thinner than a hair At the nano level, the assembly line takes the form of a microfluid platform into which an aqueous solution is pumped. This platform is essentially a canal system with the main canal just 30 micrometres wide - three times thinner than a human hair. Several inflows and outflows lead to and from the canal at right angles.

The platform was developed by Vogel's PhD student Dirk Steuerwald and the prototype was created in the clean room at the IBM Research Centre in Ruschlikon.

The canal system is fitted with a carpet made of the motor protein kinesin. This protein has two mobile heads that are moved by the energy-rich molecule ATP, which supplies the cells of humans and other life forms with energy and therefore make it the fuel of choice in this artificial system.

Assembling molecules step-by-step The ETH researchers used microtubules as assembly carriers. Microtubules are string-like protein polymers that together with kinesin transport cargo around the cells. With its mobile heads, kinesin binds to the microtubules and propels them forward along the surface of the device.

This propulsion is further supported by the current generated by the fluid being pumped into the canal system. Five inflows and outflows direct the current in the main canal and divide it into strictly separated segments: a loading area, from where the assembly carriers depart, two assembly stations and two end stations, where the cargo is delivered.

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Nanoscale assembly line