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The language of molecules

Molecules, the connections between chemical elements, are contained in all the visible and invisible objects that surround us. Yet it is little known that molecules can also be used to transfer data and are a possible alternative to radio technology.

Tube
© Anna-Kristina Pries, Uni Kiel

The movements of the molecules are measured in this two-metre-long tube.

MaMoKo, or “Macroscopic Molecular Communication”, is the collaborative project based at Kiel University's Faculty of Engineering and funded by the Federal Ministry of Education and Research, in which precisely this is being investigated under the leadership of Professor Peter Adam Höher. The observation of nature was inspirational here. Ants do not communicate acoustically, but via simple chemistry through scented molecules. These pheromones not only show the exceedingly well organised creepy-crawlies the way, but also tell them what their role is in their community.

“We've implemented the same principle here,” said Professor Höher, pointing to a tube that is two metres long and 50 centimetres in diameter. An ultraviolet lamp is attached at one end, a spray bottle at the other, and somewhere in the middle is a camera. “Essentially, that is the communication system,” explained the specialist for Information and Coding Theory, who is being supported in his project, which began at the start of 2019 and is scheduled to run until the end of 2021, by doctoral researchers Martin Damrath, Sunasheer Bhattacharjee, and occasionally Max Schurwanz.

What takes place in this system is molecular communication in air-based media, as it is known by the experts. This means that molecules that move in the medium of air communicate something to the environment. But how do the scientists get these particles to talk to each other? They simply apply good old communication theory, which states that a message should be sent, conveyed, received and understood based on a common alphabet. In this case, the sender is a spray bottle that is filled with fluorescent liquid and connected to a microcontroller – a miniature computer – and sends its message to a camera in the form of water molecules. This then conveys the message to a decoder, which decrypts its meaning.

Sending Morse code with fluorescent water molecules

To make communication like this possible requires a predefined “vocabulary” in the form of sequential changes in concentration. “It's just like with a passport,” explained Professor Höher. “Every document has a unique number that is assigned to only one person worldwide.” The difference is that in this case, molecules are used instead of letters and names.

The spray bottle sends the molecules into the tube at different rates, similarly to Morse code. Thanks to the predefined combination options, it is therefore possible to ensure that no signal resembles another. The changes in concentration are recorded by a high-resolution camera, which can take up to 960 pictures per second, according to Max Schurwanz. Its work is made easier by the fluorescent dye, which makes contrasts more distinct.

Once the intensity and time sequence in which the molecules arrive has been established, it's not long until the message can be decrypted. The Kiel-based team surrounding Professor Höher and colleagues of the MaMoKo project located around Germany have the industrial sector in mind, in which the use of radio technology is prohibited or is not possible due to a high number of disruptive factors. Larger operations in the chemical industry, for instance, have miles of pipe networks that are susceptible to leaks. Every pipe could be assigned a sequence. Thanks to the communicating molecules, the damaged pipe could be easily located using cameras, as each possible combination occurs only once.

“The procedure works in principle,” emphasized Sunasheer Bhattacharjee, who deals primarily with the mathematical aspects of the project as well as experimental set-up. Yet he agrees with the others involved that molecular communication, which has only been a scientific topic for ten years or so, holds a lot of potential for optimisation.

Better understanding the spread of viruses

The Kiel-based group has already achieved one specific goal, even though it was unplanned: both the measuring set-up and the mathematical modelling behind it have been successfully used to trace the spread of airborne infectious diseases such as COVID-19. The spray bottle is an exact representation of an infected person who releases molecules with every breath and especially every cough or sneeze. The transmission and range of aerosols was compared with and without a mask using artificially induced coughing fits with volunteer test persons, who were of course not infected with the coronavirus. The result: larger particles are expelled up to three metres with each cough. Smaller suspended particles, however, can spread far throughout the room and stay in the air for a long time, like cigarette smoke. With medical protective masks though, barely any particles can be detected.

Author: Martin Geist