Ushering in a New Generation of Green Electronics

When Jun Yao was applying for a junior faculty position in the UMass Amherst Department of Electrical and Computer Engineering around 2017, he hoped to continue his research on silicon nanowires at the university. So, he was puzzled when, during the interview process, he was scheduled to meet with Derek Lovley, research professor in the UMass Department of Microbiology.

Lovley is a microbial ecologist who studies microbes with environmental or biotechnological applications. In the 1980s, while working in the mud of the Potomac River, he discovered Geobacter, a microbe with many unique properties and interesting environmental applications. Lovley’s research group studied Geobacter for decades and discovered among its special properties that it has the ability to produce tiny electrically conducive nanowires. When Lovley described these protein nanowires to Yao during the interview, Yao practically began “jumping up and down in his seat,” Lovley recalled. “He had never heard of protein nanowires before and was very enthusiastic about studying their use in electrical engineering. Meanwhile, we had always studied them for their biological function, but their application in electrical engineering was a wide-open field. Jun was doing sophisticated things with silicon nanowires, and was the perfect person to take this to the next level.”

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Their mutual excitement during that fateful meeting turned out to be justified. Yao and Lovley’s collaboration researching protein nanowires has yielded several groundbreaking discoveries—from developing a device that literally creates electricity out of thin air to the basis for highly sensitive biomedical sensors—and is at the leading edge of a paradigm shift in electrical engineering: producing truly green electronics.

Yao and Lovley both have faculty appointments in the UMass Amherst Institute for Applied Life Sciences (IALS), which fosters interdisciplinary research and its translation to innovative product candidates, technologies, and services that benefit human health and well-being.

“This kind of interdisciplinary research is often where really bold innovation occurs,” said Lovley. “Without the connection and support offered by IALS, this collaboration likely wouldn’t have happened.”

Stuck in the Mud

In 1987, Lovely reported in Nature about his discovery of the microbe Geobacter, which could grow on iron in sediments and make unique iron minerals. His continued research into Geobacter revealed other unusual properties, including its ability to clean up uranium contamination and to convert organic matter into electricity. “During the course of that research is when we discovered the protein nanowires, which we called microbial nanowires at the time,” Lovley said.

While many scientists are pursuing development of more sustainable electronics, Lovley and Yao are rare in trying to produce them biologically—an approach requiring low energy and renewable biological inputs. It is also non-toxic and produces no e-waste, in contrast to both today’s silicon nanowires and to alternative approaches that attempt to manually construct protein nanowires from their component amino acids.

“These biologically produced protein nanowires sit at a sweet spot of being sustainably produced, extremely small, and environmentally stable enough for real applications,” said Yao.  

Moreover, through gene editing, the specific properties of the nanowires can be carefully tailored for different applications. For example, they can be made dramatically more electrically conductive or turned into highly sensitive sensors.  

“It’s a unique material because of the fine scale on which we can make these modifications,” said Lovley. “I think we’ve only scratched the surface there.”

Putting Protein Nanowires to Work

When he first began working with protein nanowires, Yao had some general ideas of what they might be able to do from an electrical engineering perspective, but he kept an open mind. Initially, the two labs sought to use protein nanowires to create a sensor that could detect humidity. But one day, Xiaomeng Liu, a PhD student working in the lab, forgot to plug in power for the device, and the researchers realized that the device still gave an electrical signal.  

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“We looked at the data and realized it’s a true signal, which means the device itself was generating power,” Yao recalled. That serendipitous discovery led to the creation of the “Air-gen,” an air-powered generator that connects protein nanowires produced by Geobacter to electrodes in order to harvest electricity from water vapor naturally present in the air. Yao and Lovley first reported on this discovery in Nature in February 2020 and, in the same year, won the Armstrong Fund for Science award, a two-year, $40,000 grant to support scaling up their invention for practical applications.

“We are literally making electricity out of thin air,” Yao said. Unlike other forms of renewable energy, Air-gen requires neither sunlight nor wind to operate, and can work in very low-humidity environments or indoors. The original Air-gen produced enough electricity to power small electronics.  

A series of discoveries based on protein nanowires followed the invention of the original Air-gen, with the research receiving funding from sources including IALS, the National Science Foundation (NSF), and the U.S. Army Combat Capabilities Development Command Army Research Laboratory. In 2022, Yao and Lovley announced in Nature Communications that they had engineered a biofilm (a layer of cells about the thickness of a sheet of paper, produced naturally by an engineered version of Geobacter) capable of producing long-term, continuous electricity from sweat. The biofilm could “plug in” to the moisture always present on the surface of our skin and convert the energy locked in evaporation into enough energy to power small devices. The researchers imagined an application in which it could be worn, like a Band-Aid, as a patch applied directly to the skin.

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Yao and Lovley have also harnessed Geobacter’s potential in creating sensors. In February 2023, in the journal Biosensors and Bioelectronics, they announced the invention of an “electronic nose.” Through gene editing of Geobacter, they trained it to produce nanowires that could “sniff out” a vast array of chemical tracers. This technology could one day be used to detect a wide range of medical conditions like asthma and kidney disease.  

“Genetically modifying the nanowires made them 100 times more responsive to ammonia than they were originally,” says Yassir Lekbach, the paper’s co-lead author and a postdoctoral researcher in microbiology at UMass Amherst. “The microbe-produced nanowires function much better as sensors than previously described sensors fabricated with traditional silicon or metal nanowires.”

The researchers have also made exciting discoveries about protein nanowires’ capacities to create intelligent systems. In 2020, Yao, Lovley, and PhD candidate Tianda Fu reported in Nature Communications that they had created a neuromorphic memristor, or “memory resistor,” device with protein nanowires. It runs extremely efficiently on very low power, as brains do, to carry signals between neurons. The following year, the team also reported in Nature Communications on developing with protein nanowires a “self-intelligent” electronic microsystem that can respond to information inputs without any external energy input, much like a self-autonomous living organism.

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With their latest research, published in May 2023 in the journal Advanced Materials, Yao and Lovley broadened the “Air-gen” effect initially discovered in protein nanowires and demonstrated that nearly any material could be turned into a device that continuously harvests electricity from humidity in the air. This is accomplished through creating in the material very tiny nanopores—holes smaller than 100 nanometers, or less than a thousandth of the width of a human hair. As water molecules pass through the pores in the thin layer of material and bump into the pores’ edges, a charge imbalance is created between the upper and lower parts of the material—much like what occurs in a cloud when it produces a lightning bolt. This would effectually create a battery that runs off humidity in the air.

This discovery offers broad choices for cost-effective and environment-adaptable fabrications. Because it’s so thin, it could be dramatically scaled up by stacking multiple layers while barely increasing the footprint of a device.

Though their research showed that this technology worked in a range of different materials, said Yao, the protein nanowires produced by microbes still appear to be, by far, the most efficient in producing electricity.

The Future of Sustainable Electronics

According to Lovley, scaling up this technology for broad application will require overcoming a limitation in the supply of Geobacter, which is slow-growing and anaerobic—meaning it only grows in environments devoid of oxygen. Lovely’s lab has shown that E. coli, a microbe that grows rapidly in air, can be genetically engineered to produce a diversity of different protein nanowires, just like Geobacter. Yao is currently planning a collaboration with a former post-doc from Lovley’s lab, now at the University of California, Berkeley, to explore large-scale production of nanowires.

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Going forward, Yao and Lovley are continuing to explore other applications of protein nanowires, such as creating sensors that work in liquid (for example, to detect certain molecules in blood). With their combined sensing, memory storage, and electricity generation capabilities, protein nanowires seem primed to create “a very holistic package for making wearable biomedical sensors,” said Lovley.

Yao is also interested in scaling up the technology’s electricity generation capabilities to make a major contribution to sustainable energy production.

“If we can scale up the Air-gen—which I think is fundamentally feasible—I envision this technology could really be deployed anywhere,” he said. “It could be painted on the walls of your home or underneath your desk. It could even be in forests, where current renewable energy technologies like solar panels don’t work because the sun is blocked. I dream that one day, this really could revolutionize society.”

 

This story was originally published in July 2023.