Bacteria 'mini-skyscrapers' convert light into electricity

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A very particular type of bacteria has just been “rehoused” with great fanfare. Researchers at the University of Cambridge have designed tiny “skyscrapers” for it, which allow it to generate electricity from sunlight and water.

Scientists have indeed 3D printed grids of “nano-housings” in height, on the scale of bacteria. These structures were created in nanoparticles of indium tin oxide, and allow its inhabitants to quickly develop a colony there. However, this “housing” is not free! These mini “skyscrapers” are actually electrodes, since researchers expect bacteria that take up residence there to produce energy that can be used by humans.

Indeed, it is a particular type of bacteria that is targeted by this innovation: cyanobacteria, or photosynthetic bacteria. According to ANSES’s definition, “ cyanobacteria are micro-organisms that have been present on Earth for two to three billion years. Present throughout the world, in plants, in water, but also in sand, they shape our planet. (…) When the environmental conditions – temperature, nutrients – are favorable to them, they can proliferate massively and quickly, sometimes in just a few days
”.

This is what makes this bacterium, when it develops a lot in water, can give this green color and these Bad odors that are not very appreciated… As you will have understood, cyanobacteria are anything but a rare resource. It is this prolixity, associated with one of their particularities, which makes them so interesting for scientists. Indeed, they have the particularity of being able to carry out photosynthesis and naturally produce electrons as “waste”.

The theory therefore seems rather simple: it would suffice to “connect” these bacteria to electrodes to recover natural energy from photosynthesis. However, many scientists have tried it without really achieving exploitable results, explain the researchers in a press release from the University of Cambridge: “ It there has been a bottleneck in how much energy you can actually extract from photosynthetic systems, but no one has figured out where it is ”, explains Jenny Zhang of the Yusuf Hamied Department of Chemistry, who led the research. “Most scientists assumed it was on the biological side, in bacteria, but we found that a substantial bottleneck is actually located on the material side”.

A “mini-city” to make bacteria live in community

Indeed, depending on how the bacteria are installed, it seems that we can recover more or less electricity. Several constraints come into play. To recover the energy produced, the bacteria must be connected to electrodes. On the other hand, to produce a lot of energy, they must be in a very bright place, like the surface of a lake in summer. These bacteria also live in a “community” and should therefore not be too isolated.

It is therefore by taking into account all these parameters that the team of researchers has designed a nanostructure made up of electrodes that form very small pillars adapted to the lifestyle of bacteria. For this, they have developed a 3D printing method capable of controlling several length scales, making the structures very customizable.

diagram cyanobacteria photosynthesis nanostructures
a) Schéma d’une cellule chimique biophotoélectrique produisant de l’électricité solaire biologique en utilisant des biofilms photosynthétiques comme photocatalyseurs. Le flux d’électrons provenant de l’oxydation photosynthétique de l’eau est récolté
à l’anode et transféré à une cathode, qui réduit l’oxygène en nanoparticules de H²O.

b) Schéma de l’interface cyanobactérie-anode. La lumière est récoltée par le photosystème II (PSII), qui est utilisé pour oxyder
l’eau entraînant la libération d’électrons, O2 et H+. Les électrons sont transférés via la chaîne de transport d’électrons photosynthétique au photosystème I (PSI), qui pompe l’énergie lumineuse absorbée
dans les électrons.

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a) Diagram of a cell biophotoelectric chemical producing biological solar electricity by using photosynthetic biofilms as photocatalysts. Electron flux from photosynthetic oxidation of water is harvested at the anode and transferred to a cathode, which reduces the oxygen to H2O nanoparticles.

b) Diagram of the cyanobacterium-anode interface. Light is harvested by photosystem II (PSII), which is used to oxidize water, resulting in the release of electrons, O2 and H+. Electrons are transferred via the photosynthetic electron transport chain to photosystem I (PSI), which pumps the absorbed light energy into electrons. © Jenny Z. Zhang et al./Cambridge University

« The electrodes have excellent properties of light management, like a high-rise apartment with lots of windows”, explains Jenny Zhang, who draws parallels with skyscrapers. “ Cyanobacteria need something they can attach to and form a community with their neighbors. Our electrodes allow a balance between a large surface and a lot of light, like a glass skyscraper ”. The final structure could also be compared to a miniature city made up of skyscrapers.

Once installed in this way, the bacteria turned out to be productive, and the researchers were also able to closely observe the way in which they convert the light, in order to optimize its recovery. “Our approach allows us to exploit their energy conversion pathway at a pr ecoce, which helps us understand how they perform energy conversion so that we can use their natural pathways for the production of renewable fuels
”, they say.

Energy recovery has therefore reached a level of efficiency that could make it usable among other forms of renewable energy. The researchers even claim that the method is more effective than certain biotechnological technologies currently in use, particularly in the creation of biofuels. “ Our approach is a step towards making even more sustainable renewable energy devices for the future”, therefore welcomed Jenny Zhang. The study nevertheless specifies that the nanostructures are composed of indium tin, a material known to be rare and non-renewable.

Source: Nature Materials