A novel electric propulsion technology for nanorobots: 100K Faster computer controls for molecular machines


fastcomputerElectric fields drive the rotating nano-crane – 100,000 times faster than previous methods. Credit: Enzo Kopperger / TUM

Scientists at the Technical University of Munich (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. This makes nanobots fast enough to do assembly line work in molecular factories. The new research results will appear as the cover story on 19th January in the renowned scientific journal Science.

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. Prof. Friedrich Simmel observes the movement of the nanomachines on the monitor of a fluorescence microscope. A simple mouse click is all it takes for the points of light to move in another direction.

“By applying electric fields, we can arbitrarily rotate the arms in a plane,” explains the head of the Chair of Physics of Synthetic Biological Systems at TU Munich. His team has for the first time managed to control nanobots electrically and has at the same time set a record: The new technique is 100 000 times faster than all previous methods.

DNA-origami robots for the manufacturing plants of tomorrow

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.

The only reason these  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.

Fast computer control for molecular machines
Rotation of the arm between two docking points (red and blue). Credit: Enzo Kopperger / TUM

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.

Electronic speed boost

“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, who is also the co-coordinator of the Excellence Cluster Nanosystems Initiative Munich (NIM).

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 impulses.

Robotic movement under the microscope

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 produced by the lead author Enzo Kopperger 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.

In collaboration with fluorescence specialists headed by Prof. Don C. Lamb of the Ludwig Maximillians University Munich, the researchers marked the tips of the  using pigment molecules. They observed their motion using a . 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 experiment demonstrated that molecular machines can be moved, and thus also driven electrically,” says Simmel. “Thanks to the electronic control process, we can now initiate movements on a millisecond time scale and are thus 100 000 times faster than with previously used biochemical approaches.”

On the road to a nanofactory

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, emphasizes Simmel. “Nanobots are small and economical. Millions of them could work in parallel to look for specific substances in samples or to synthesize complex molecules – not unlike an .”

 Explore further: Scientists create world’s first ‘molecular robot’ capable of building molecules

More information: Enzo Kopperger et al. A self-assembled nanoscale robotic arm controlled by electric fields, Science (2018). DOI: 10.1126/science.aao4284

 

Magnetic nanoparticles enhance performance of solar cells: Technical University of Munich


1-magneticnanoMagnetic nanoparticles can increase the performance of solar cells made from polymers – provided the mix is right. This is the result of an X-ray study at DESY’s synchrotron radiation source PETRA III. Adding about one per cent of such nanoparticles by weight makes the solar cells more efficient, according to the findings of a team of scientists headed by Prof. Peter Müller-Buschbaum from the Technical University of Munich. They are presenting their study in one of the upcoming issues of the journal Advanced Energy Materials (published online in advance).

Polymer, or organic, solar cells offer tremendous potential: They are inexpensive, flexible and extremely versatile. Their drawback compared with established is their lower efficiency. Typically, they only convert a few per cent of the incident light into electrical power. Nevertheless, organic solar cells are already economically viable in many situations, and scientists are looking for new ways to increase their efficiency.

One promising method is the addition of nanoparticles. It has been shown, for example, that absorb additional sunlight, which in turn produces additional electrical charge carriers when the energy is released again by the gold particles.

Müller-Buschbaum’s team has been pursuing a different approach, however. “The light creates pairs of charge carriers in the solar cell, consisting of a negatively charged electron and a positively charged hole, which is a site where an electron is missing,” explains the main author of the current study, Daniel Moseguí González from Müller-Buschbaum’s group. “The art of making an organic solar cell is to separate this electron-hole pair before they can recombine. If they did, the charge produced would be lost. We were looking for ways of extending the life of the electron-hole pair, which would allow us to separate more of them and direct them to opposite electrodes.”

Crystalline structures within polymer solar cells cause characteristic diffraction patterns in experiments with synchrotron radiation. Credit: Credit: TU München

This strategy makes use of a quantum physical principle which states that electrons have a kind of internal rotation, known as spin. According to the laws of quantum physics, this spin has a value of 1/2. The positively charged hole also has a spin of 1/2. The two spins can either add up, if they are in the same direction, or cancel each other out if they are in opposite directions. The electron-hole pair can therefore have an overall spin of 0 or 1. Pairs with a spin of 1 exist for longer than those with an overall spin of 0.

The researchers set out to find a material that was able to convert the spin 0 state into a spin 1 state. This required nanoparticles of heavy elements, which flip the of the electron or the hole so that the spins of the two particles are aligned in the same direction. The iron oxide magnetite (Fe3O4) is in fact able to do just this. “In our experiment, adding magnetite nanoparticles to the substrate increased the efficiency of the solar cells by up to 11 per cent,” reports Moseguí González. The lifetime of the electron-hole pair is significantly prolonged.

Adding nanoparticles is a routine procedure which can easily be carried out in the course of the various methods for manufacturing organic solar cells. It is important, however, not to add too many nanoparticles to the solar cell, because the internal structure of organic solar cells is finely adjusted to optimise the distance between the light-collecting, active materials, so that the pairs of charge carriers can be separated as efficiently as possible. These structures lie in the range of 10 to 100 nanometres.

“The X-ray investigation shows that if you mix a large number of nanoparticles into the material used to make the solar cell, you change its structure”, explains co-author Dr. Stephan Roth, head of DESY’s beam line P03 at PETRA III, where the experiments were conducted. “The solar cell we looked at will tolerate magnetite nanoparticle doping levels of up to one per cent by mass without changing their structure.”

The scientists observed the largest effect when they doped the substrate with 0.6 per cent nanoparticles by weight. This caused the efficiency of the polymer solar cell examined to increase from 3.05 to 3.37 per cent. “An 11 percent increase in energy yield can be crucial in making a material economically viable for a particular application,” emphasises Müller-Buschbaum.

The researchers believe it will also be possible to increase the efficiency of other by doping them with nanoparticles. “The combination of high-performance polymers with holds the promise of further increases in the efficiency of organic in the future. However, without a detailed examination, such as that using the X-rays emitted by a synchrotron, it would be impossible to gain a fundamental understanding of the underlying processes involved,” concludes Müller-Buschbaum.

 Explore further: New technique helps probe performance of organic solar cell materials

More information: Advanced Energy Materials, 2015; DOI: 10.1002/aenm.201401770