Molecular machines: Piecework at the nano assembly line

Jan 31, 2018

Scientists at LMU and TUM have developed a novel electric propulsion technology for nanorobots. It allows molecular machines to move a hundred thousand times faster than with the biochemical processes used to date.

Rotation of the nano-arm between two docking points (red and blue). Image: Enzo Kopperger / TUM

Up and down, up and down. The points of light alternate back and forth in lockstep. They are produced by glowing molecules affixed to the ends of tiny robot arms. A simple mouse click is all it takes for the points of light to move in another direction. By applying electric fields, the arms can be arbitrarily rotated in a plane. Don Lamb, Professor at LMU’s Department of Chemistry, and Friedrich Simmel, head of the Chair of Physics of Synthetic Biological Systems at TUM, now present their research results in the renowned scientific journal Science. The team has, for the first time, managed to control nanobots electrically, and at the same time, set a record: The new technique is 100 000 times faster than all previous methods.

Scientists around the world are working on new technologies for the nanofactories of the future. They hope these will one day be used to analyse biochemical samples or produce active medical agents. The required miniature machines can already be produced cost-effectively using the DNA-origami technique. One 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 perform their 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.

Robotic movement under the microscope

“Building up a nanotechnological assembly line calls for a different kind of propulsion technology. We came up with the idea of dropping biochemical nanomachine switching completely in favour of the interactions between DNA structures and electric fields,” explains TUM researcher Simmel. The principle behind the propulsion technology is simple: DNA molecules have negative charges. The biomolecules can thus be moved by applying electric fields. Theoretically, this should allow nanobots made of DNA to be steered using electrical fields.

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 by 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.

To visualize the functions of those tiny nanobots, highend microscopy and analysis techniques are necessary. In collaboration with fluorescence specialists headed by Prof. Don Lamb, the researchers marked the tips of the robot arms using dye molecules. They observed their motion using a fluorescence microscope. They then changed the direction of the electric field. This allowed the researchers to arbitrarily alter the orientation of the arms and control the locomotion process.

The new control technology is suited not only for moving around dye molecules and nanoparticles. The arms of the miniature robots can also be used to apply force to molecules. These interactions can be utilized for diagnostics and in pharmaceutical development. (TUM/LMU)
Science 2018