Scientists around the world are working on new technologies for the nanofactories of the future, which one day could be used to analyze biochemical samples or produce active medical agents. The required miniature machines can already be produced costeffectively using the DNA-origami technique.

Electric fields drive a rotating nano-crane 100,000 times faster than previous methods. (Enzo Kopperger/TUM)

The only reason these molecular machines have not been deployed on a large scale to date is that they are too slow. The building blocks are activated with enzymes, strands of DNA, or light to then perform specific tasks; for example, to gather and transport molecules. However, traditional nanobots take minutes to carry out these actions — sometimes even hours. Therefore, efficient molecular assembly lines cannot, for all practical intents and purposes, be implemented using these methodologies.

Building up a nanotechnological assembly line calls for a different kind of propulsion technology. A new technology substitutes biochemical nanomachine switching for the interactions between DNA structures and electric fields. The principle behind the propulsion technology is simple: DNA molecules have negative charges. The biomolecules can thus be moved by applying electric fields. The oretically, this should allow nanobots made of DNA to be steered using electrical impulses.

The electric propulsion technology for nanorobots allows molecular machines to move 100,000 times faster than with the biochemical processes used to date. This makes nanobots fast enough to do assembly line work in molecular factories. By applying electric fields, the robot arms can arbitrarily rotate in a plane.

To determine whether and how fast the robot arms would line up with an electric field, the researchers affixed several million nanobot arms to a glass substrate, and placed this into a sample holder with electrical contacts designed specifically for the purpose. Each of the miniature machines comprises a 400-nanometer arm attached to a rigid, 55 ¥ 55-nanometer base plate with a flexible joint made of unpaired bases. This construction ensures that the arms can rotate arbitrarily in the horizontal plane.

The tips of the robot arms were marked using pigment molecules. Motion was observed using a fluorescence microscope. Then the direction of the electric field was changed, allowing the researchers to arbitrarily alter the orientation of the arms and control the locomotion pro cess. The experiment dem onstrated that molecular machines can be moved, and thus also driven electrically.

The new control technology is suited not only for moving around pigments and nanoparticles — the arms of the miniature robots can also apply force to molecules. These interactions can be utilized for diagnostics and in pharmaceutical development. Millions of the nanorobots could work in parallel to look for specific substances in samples, or to synthesize complex molecules — not unlike an assembly line.

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