Scientists are developing technologies to use electrical nanowires buried in the ground and oceans

The study published in the journal nature communication, comes from researchers at Yale University. To further explore the details of the study and the implications of the discovery, Interesting Engineering spoke to the publication’s senior author, Nikhil Malvankar, associate professor of molecular biophysics and biochemistry at the Microbial Sciences Institute at Yale, where he directs the Malvankar Protein Nanowire Lab.

How do the nanowires work?

Essentially, all living things require oxygen to expel excess electrons during the process of converting nutrients into energy. But what happens when there is no access to oxygen, for example in the ground or deep at the bottom of an ocean? It turns out that some bacteria have adapted to this dilemma, essentially “breathing” minerals through very small protein filaments, or “nanowires.”

In addition, the scientists found a specific bacterium that can be manipulated to produce these nanowires on an industrial scale. As noted by Professor Malvankar, they discovered that a “bacterium called Geobacter has evolved over billions of years how it communicates electronically with the outside world” by using nanowires made up of chains of “heme” molecules, just like those that carry oxygen in our blood. But instead, Geobacter’s malice transmit electricity. The micron-long heme chains provide a continuous pathway for electrons.

When the bacteria are fed light, “you actually get almost 100 times more electricity,” revealed Malvankar.

The secret ingredient

How does Geobacter do this? Because Geobacter is a very common bacterium found in the soil beneath our feet, Malvankar believes it offers the solution to what he believes to be the biggest bottleneck problem they need to solve – “how can we make large-scale living systems efficient.” connect to electronics ?”

The key lies in the discovery of a metal-containing protein called cytochrome OmcS, which acts as a natural photoconductor. According to Malvankar, this was their most important discovery. The metal gives the bacterial nanowires high electron conductivity.

“You look like real wire. The heme molecule is like a wire and the protein is like insulation around the wire,” the scientist explained, comparing it to the insulation found in our phone chargers.

Why do some bacteria need nanowires?

The answer, according to Malvankar, lies in the quote “Life is nothing but an electron looking for a place to rest” by Albert Szent-Györgyi, a biochemist who discovered the cycle of oxygen metabolism and received the 1937 Nobel Prize in “Physiology or Medicine”. “

Growing nanowires allows the bacteria to survive without the presence of oxygen. The bacteria use the wires to send electrons, giving them access to a much larger area. Light accelerates bacterial respiration due to rapid electron transfer between nanowires.

“What excites me about this work is that it expands the range of how far electrons can travel in a living system,” Malvankar shared, adding, “typically, in humans, an electron can only exceed a nanometer, or a billionth of a meter, because proteins aren’t very good at moving electrons for very long. While here the electrons can travel hundreds of microns.” That makes it almost several million times longer, thanks to the network of nanowires.

How the nanowires are made

Malvankar shared that they can now make these multifunctional “living electronics” much faster and at a lower cost.

A big plus of the material in the wires is that it combines useful properties – it is self-repairing, flexible, biodegradable and non-toxic. Malvankar compared it to silicon, which works well under certain conditions, while the nanowires are even more flexible. They can work in a range of different and extreme environments – at high and extremely low temperatures or in low-acid situations – while remaining very stable and robust.

As for production, the nanowires can now be grown in the lab and retain their properties even when not alive.

The scientists can use the bacteria to grow the wires, then “put them in a blender” to get rid of the bacteria and leave only the “cleaned filaments – the wires that are then strong enough to use”.

What are possible applications for the nanowires?

Malvankar sees a number of exciting applications for the biomaterials they are developing that would be cheaper, faster and more precise than other current technologies of this type.

The nanowires could be very useful in combating greenhouse gas emissions that lead to rising temperatures and a warming of the planet. As they develop the nascent field of electrogenetics (which uses electrical stimulation to control biological processes), the researchers aim to figure out how to activate the electrical grid on the seafloor to prevent methane from being released into the atmosphere.

As Malvankar elaborated, they hope to “put electrodes in the ocean or in the ground, and those electrodes will be used to induce these electrical connections between bacteria. And that could be a way to locally stop the release of methane into the environment or locally rid the environment of toxic pollutants. So if there is an oil spill, these bacteria can eat oil. So we can accelerate this process locally by using these electrodes.”

The nanowires could also be a revolutionary tool for use in DNA sequencing, data processing, light collection or health monitoring, creating a new generation of self-sufficient body sensors that measure glucose or oxygen levels.

Another application of these wires stems from the fact that “they exhibit properties that no other protein has had before,” according to the scientist. The wires his lab is working on are highly adaptable and work particularly well at very low temperatures. When the scientists cooled them, electron transfer actually accelerated by a factor of 300. This could work for low temperature sensors or other electronics that need to work under extreme conditions.

One such extreme condition could be outer space — specifically, exploration of Mars. Malvankar speculates that it might be possible to use their methods to trick the bacterial nanowires into producing certain chemicals, biofuels, or nutrients needed to colonize Mars. It may also turn out that Mars, whose soil is particularly rich in iron, already has such bacteria on its surface. By using their techniques to activate it, the scientists could “essentially mimic how we evolved life on Earth,” Malvankar suggested.

Study Summary:

Light-induced microbial electron transfer has potential for efficient production of value-added chemicals, biofuels, and biodegradable materials due to diversified metabolic pathways. However, most microbes lack photoactive proteins and require synthetic photosensitizers that suffer from photocorrosion, photodegradation, cytotoxicity, and the formation of photoexcited radicals that are harmful to cells, severely limiting catalytic performance. Therefore, there is an urgent need for biocompatible photoconductive materials for an efficient electronic interface between microbes and electrodes. Here we show that living biofilms of Geobacter sulfurreducens use cytochrome OmcS nanowires as intrinsic photoconductors. Photoconductive atomic force microscopy reveals up to a 100-fold increase in photocurrent in cleaned individual nanowires. Photocurrents react quickly (< 100 ms) to the excitation and persist reversibly for hours. Femtosecond transient absorption spectroscopy and quantum dynamics simulations reveal ultrafast (~200 fs) electron transfer between nanowire hemes upon photoexcitation, improving charge-carrier density and mobility. Our work unveils a new class of natural photoconductors for whole-cell catalysis.