In 1987, the microbiologist Derek Lovley made a surprising discovery. While digging through the mud of the Potomac River in Washington DC, he encountered a strain of bacteria with properties that had never been seen before.
The bacteria, which he christened Geobacter metallireducens, were able to survive without oxygen or sunlight thanks to their unusual dietary habits. They ‘eat’ and ‘breathe’ metals such as iron, feeding on waste compounds and passing their energy onto metal oxides outside the cell.
It didn’t take Lovley long to realise the implications: since these bacteria ‘eat’ organic compounds, they could potentially be used to clean toxic waste. By the early 2000s, Lovley had found 70 types of Geobacter, which were variously used to decontaminate an oil spill and a uranium mine.
The possibilities, however, didn’t end there. When a Geobacter bacterium ‘breathes’, it excretes electrons, passing them down tiny wires that protrude from its surface. These wires – dubbed ‘microbial protein nanowires’ – make the bacteria a natural electricity source.
“The bacteria produce these protein nanowires as part of their metabolism and also to communicate with their neighbours,” explains Alexander Smith, a biomedical engineering PhD student at the University of Massachusetts (UMass) Amherst, who works with Lovley. “Because of that, these microbial filaments are electrically conductive, and that’s a pretty interesting property – they’re basically like a biologically made electronic material. You can fit thousands of these protein nanowires in the width of one human hair.”
Over the decades since Geobacter were discovered, research in the field has advanced rapidly. Most recently, Lovley’s team has found a way to combine the protein nanowires with a non-conductive polymer, producing a flexible electronic composite material. The material in question, which can function even under harsh conditions, is suitable for manufacturing sensors and electronic devices.
Once limited to small quantities of protein nanowires (those that were produced naturally), the researchers are now working on scaling up production, generating the nanowires in commercially useful quantities.
“We can genetically modify the bacteria to produce even more of these protein nanowires in abundance. We’re then able to purify the protein nanowires and discard the rest of the cell, so that we can use the nanowires to make materials,” explains Smith.
They have made the jump from microbiology to engineering, from mud to material science. This could open the door to all kinds of commercial applications.
“In the past, Derek’s research has been about characterising these microbes and studying their properties,” says Smith. “He was also involved in projects where they were using the microbes for different applications such as bioremediation and fuel cells. But it wasn’t until recently that we discovered how these protein filaments could be purified from the bacteria and used as a material. All of a sudden we have the opportunity to produce a biologically made material that can be used to make devices for different applications.”
Green electricity
The advantages are obvious. Not only are these protein nanowires electrically conductive and super-sensitive – easily rivalling human-made materials such as carbon nanotubes or silicon nanowires – but they’re highly sustainable to produce.
In fact, protein nanowires could spell the beginning of a truly green field of electronics, free from the toxic components that make electronic waste such a concern. While today’s electronic devices are predominantly considered disposable, they are nonbiodegradable and difficult to recycle. With the dawn of electronic biologics, this could be about to change.
“The process to make carbon nanotubes and other traditional materials is pretty nasty, requiring toxic chemicals and reactions,” says Smith. “By contrast, these protein nanowires are produced by the Geobacter naturally – all we have to do is feed the bacteria with renewable feedstocks. So we have this sustainable and inexpensive way to produce the protein nanowires even at scale, eliminating a lot of the toxic chemical production that’s used with current technology.”
Another benefit of the nanowires is their versatility. Through tweaking the Geobacter, it is possible to produce different types of nanowires suitable for different forms of biomedical and environmental sensing.
“Since it’s a biologically made protein, we can genetically modify different strains of protein nanowires so they are sensitive to very specific analytes,” says Smith. “One of the biggest challenges in sensors nowadays is making them really selective, so that’s a challenge we can conquer with our protein nanowires, by functionalising them with highly selective molecules.”
Solving this challenge has been Smith’s key focus during his PhD career. An enterprising and commercially minded young researcher, he had read about Lovley’s work in the field, and quickly caught wind of the possibilities.
“I was on a mission to look for technologies at the UMass Amherst campus that could be viable products,” he says. “I came across Dr Lovley’s patent for biological microbial protein nanowires, and as I was reading about them I decided I needed to talk to this man more. So I sent him an email out of the blue, and he agreed to meet with me the next day. As he was telling me about them I just became more and more fascinated and saw the potential. I said, wow, we need to commercialise these, they’re so cool. Derek said that one of the big challenges, though, is finding the right application and the right businessperson to translate the research. So I rounded up some business mentors and we formed a team.”
The result was e-Biologics, a start-up dedicated to commercialising the protein nanowires. Five months after Smith’s meeting with Lovley, his fledgling company won first prize in the UMass Amherst 2018 Innovation Challenge, going home with $30,000 in funding.
That summer, he participated in the Berthiaume Centre Summer Accelerator, which provided further funding and gave him a crash course in launching ventures. The company is now moving towards making device prototypes and applying for patents.
“My PhD research is focused on developing the technology for the protein nanowire devices, and then my activities with the start-up company will be taking the technology that I’m developing and putting it to use for practical applications,” explains Smith.
To begin with, the e-Biologics team is focusing on a single biomedical application, which Smith describes as the original vision for their minimum viable product – something that will pave the way for more complex biomedical sensors. It is a skin sensor patch, worn like an Elastoplast, which can be used to detect the early signs of diabetic ketoacidosis
Protein nanowires can be stabilised in water, which makes them ideal for detecting metabolites in sweat. They are particularly good at gauging acidity, with their conductivity changing in response to changes in pH.
“With the help of my business mentors, I came up with the concept of a wearable device that would analyse your sweat continuously and noninvasively to measure biomarkers that can indicate the early onset of diseases,” says Smith. “Sure enough, there’s a condition called diabetic ketoacidosis, which particularly affects people with type 1 diabetes and is indicated by changes in pH.”
The device will be linked to a smartphone app that alerts the wearer to the possible onset of ketoacidosis. It will be marketed to high-risk patients with type 1 diabetes, and could ultimately prevent many hospital bills and trips to the emergency room.
This, however, is only the beginning. As Smith explains, the protein nanowires constitute a kind of platform technology that could be used for all kinds of purposes in the future.
“While these protein nanowires are responsive to pH initially, we can genetically tune them so they can respond to other analytes as well,” he says. “The vision is that we could measure many analytes simultaneously in a very small space.”
They would look not just at sweat, but also at other biological fluids such as urine, saliva and breath. This could provide an assessment of many diseases, such as Parkinson’s disease, Alzheimer’s disease and cancers.
“Because the sensor is so small and biocompatible, our vision is that it could be placed pretty much anywhere in or on the body with a very small footprint, and would be able to measure many analytes simultaneously, providing a comprehensives assessment of a patient’s health,” says Smith. “Not just diseases, but applications like nutrition and fitness tracking as well. Providing personalised monitoring of a person’s health in real time is very exciting.”
Industrial use
Since the nanowires can also be used as gas sensors, there are potential industrial uses in the works too. In these cases, the sensor would be integrated into something like a microchip, which could be used for gas sensing within chemical processing. This in itself could have implications for human health.
“During production of industrial materials such as fertiliser, if toxic gases are produced and people inhale them that can make them sick,” says Smith. “So we can make sensors that detect the presence of dangerous gases to prevent health problems from occurring.”
While e-Biologics is still in its early stages, the future certainly looks promising. The next step, says Smith, will be to rent a space in the University Of Massachusetts Institute for Applied Life Sciences, where the company will set up shop and continue to produce the technology. He is also looking to apply for further sources of funding, such as non-dilutive government grants.
Over the next few years, the team hopes to move on to testing their sensing devices with animals and eventually humans. Eventually, they want to move beyond their prototypes into a whole host of applications.
For Smith, putting these protein nanowires to good use is “a goal not just for the start-up but also for my life”. And for his mentor, Lovley, who has spent over three decades focusing on the Geobacter bacteria, the latest developments are no less exciting.
“Derek has studied these protein nanowires for their interesting microbiological properties, but he’s thrilled to see them used in an actual application that is clinically relevant and can help people,” says Smith. “He loves the interdisciplinary nature of the project, combining microbiologists with engineers and businesspeople – it’s this whole new startup environment that has been super productive for research and for translating the research. At one point he told me, ‘I never imagined that these applications could arise when I was studying Geobacter rolling around in the mud.’ And now it’s got the potential to save people’s lives.”
