Some bacteria have a superpower that scientists would love to harness. These microbes capture energy from light, just as plants do. Scientists have wanted to tap these bacteria to make electricity. But in previous research, they didn’t survive long on artificial surfaces. Researchers have now moved them to a living surface — a mushroom. Their creation is the first mushroom to make electricity.
Sudeep Joshi is an applied physicist. He works at the Stevens Institute of Technology in Hoboken, N.J. He and his colleagues turned that mushroom — a fungus — into a mini energy farm. This bionic mushroom combines 3-D printing, conductive ink and bacteria to generate electricity. Its design could lead to new ways of combining nature with electronics.
Cyanobacteria (sometimes called blue-green algae) make their own food from sunlight. Like plants, they do this using photosynthesis — a process that splits water molecules, releasing electrons. The bacteria spit out many of these stray electrons. When enough electrons build up in one place, they can create an electrical current.
The researchers needed to clump a lot of these bacteria together. They decided to use 3-D printing to deposit them precisely onto a surface. Joshi’s team chose mushrooms for that surface. After all, they realized, mushrooms naturally host communities of bacteria and other microbes. Finding test subjects for their tests was easy. Joshi simply went to the grocery store and picked up white button mushrooms.
Printing on those mushrooms, though, turned out to be a real challenge. 3-D printers have been designed to print on flat surfaces. Mushroom caps are curved. The researchers spent months writing computer code to solve the problem. Eventually, they came up with a program to 3-D print their ink onto the curved mushroom tops.
The researchers printed two “inks” onto their mushrooms. One was a green ink made of cyanobacteria. They used this to make a spiral pattern on the cap. They also used a black ink made of graphene. Graphene is a thin sheet of carbon atoms that’s great at conducting electricity. They printed this ink in a branching pattern across the mushroom top.
Then it was time to shine.
“Cyanobacteria are the real hero[es] here,” says Joshi. When his team shone light on the mushrooms, the microbes spit out electrons. Those electrons flowed into the graphene and created an electric current.
The team published its results November 7, 2018, in Nano Letters.
Experiments like this are called “proof of concept.” They confirm an idea is possible. The researchers showed their idea worked, even if it’s not yet ready for practical use. Achieving even this much took a few clever innovations. The first was getting the microbes to accept being rehoused on a mushroom. A second biggie: figuring out how to print them on a curved surface.
To date, Joshi’s group has generated a roughly 70 nanoamp current. That’s small. Really small. It’s about a 7-millionth the current needed to power a 60-watt light bulb. So clearly, bionic mushrooms won’t be powering our electronics right away.
Still, Joshi says, the results show the promise in combining living things (such as bacteria and mushrooms) with non-living materials (such as graphene).
It’s noteworthy that the researchers have convinced the microbes and mushrooms to cooperate for a short while, says Marin Sawa. She’s a chemical engineer at Imperial College London in England. Although she works with cyanobacteria, she was not part of the new study.
Pairing two life forms together is an exciting area of research in green electronics, she says. By green, she’s referring to an eco-friendly technology that limits waste.
The researchers printed cyanobacteria on two other surfaces: dead mushrooms and silicone. In each case, the microbes died out within about a day. They survived more than twice that long on the live mushrooms. Joshi thinks the microbes’ long life on the living mushroom is proof of symbiosis. That’s when two organisms coexist in a way that helps at least one of them.
But Sawa isn’t so sure. To be called symbiosis, she says the mushrooms and bacteria would have to live together a lot longer — at least a week.
Whatever you call it, Joshi thinks it’s worth tweaking. He thinks this system can be greatly improved. He’s been gathering ideas from other researchers. Some have suggested working with different mushrooms. Others have advised tweaking the genes of the cyanobacteria so that they make more electrons.
“Nature gives you lots of inspiration,” Joshi says. Common parts can work together to produce surprising results. Mushrooms and cyanobacteria grow in many places, and even graphene is just carbon, he notes. “You observe it, you come to the lab and start experiments. And then,” he says, if you’re really lucky “the light bulb will go off.”
This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.