Imagine a world where electronic devices are powered by living organisms and biodegrade after use, eliminating the problem of electronic waste. This isn't the plot of a futuristic sci-fi movie-it's a real, growing area of research known as bioelectronics. Microbes, naturally, are the stars of this show.
Microbial activity has shaped the chemistry of Earth and actively drives biogeochemical cycles. But ever since scientists stumbled upon what are known as electroactive microbes, the potential to revolutionize electronics, creating more sustainable, eco-friendly technologies, is increasingly being explored.
Microbes That Generate Electricity
As the name suggests, electroactive microbes can generate electricity. For over a decade, microbes like Shewanella and Geobacter have dominated research in microbial electroactivity. These bacteria live in environments where oxygen is limited or absent and rely on a remarkable energy strategy: they transfer electrons out of their cells onto conductive terminal electron acceptors like minerals. Essentially, they can "breathe" metals instead of oxygen, and in doing so, they generate electricity.
Scientists have leveraged electroactivity to create bioelectrochemical systems, which use electrodes as a substitute for the minerals that these microbes would naturally use as their terminal electron acceptors. Thus, these systems use microbes as catalysts to generate electricity by reducing the electrode. Bioelectrochemical systems have come a long way since their conception and have branched out into several applications, like wastewater treatment, recovery of heavy metals, biosensing to detect contaminants in water and soil and carbon capture.
However, these bacteria (and bioelectrochemical systems) have limitations. Their electron transfer only occurs over short distances-micrometers-meaning their applications, while promising, have remained limited in scope. However, in recent years, a new microbe was discovered that takes electron transfer to a whole new level.
The Discovery of Cable Bacteria: Nature's Electric Wires
The discovery of cable bacteria in 2012 was a groundbreaking event in biology and opened new possibilities in bioelectronics. Cable bacteria connect oxidation of sulfide and reduction of oxygen via electron transfer over centimeter-distances. Picture a long, filamentous bacterium with a conductive "wire" running through its body, allowing electrons to flow from one end of the entire structure to the other, like an electric cable. This is exactly what cable bacteria do in their natural habitats, typically marine and freshwater sediments. Their ability to conduct electrons across such long distances is fascinating from a bioelectronics standpoint. Scientists are still unraveling the structure of the conductive periplasmic wire, but their remarkable qualities are already capturing the imagination of scientists and innovators alike.
Bioelectronics: Integrating Conductive Microbial Structures into Electronics
So, how does this research go from the ocean floor to high-tech electronics? While the idea of living and breathing electronics might sound like science fiction, research in this area is advancing. One of the most exciting applications of electroactive bacteria like Geobacter and cable bacteria is in the development of biological electronics. Conductive nanowires from Geobacter can be produced on a mass scale, extracted and integrated into electronic circuits. These nanowires have been used in thin film circuits to generate electricity from ambient humidity. The advantage of such materials lies in the fact that they can conduct electricity while remaining biodegradable and non-toxic, thus, introducing the potential to create biodegradable electronics that would degrade naturally at the end of their life cycle.
Scientists are also exploring how mineral-encrusted bacteria could be used in electronic components. Some electroactive microbes, including Geobacter and cable bacteria, produce conductive mineral layers-such as iron and manganese oxides-along their filaments. These encrustations could further enhance the ability to store and transfer electrical energy. This is where the idea of microbial "batteries" or biological capacitors comes in-living devices that can store and release energy, just like the capacitors in your phone or laptop.
Imagine powering sensors used to explore remote environments-like deep-sea exploration, or even in outer space-using bacteria that generate their own electricity. In fact, microbial fuel cells have been used to generate energy from microbes and power a meteorological buoy. Recent studies suggest that certain minerals produced by these microbes are even photoactive, meaning they could be used in solar-powered devices, with applications in microbial-based solar energy generation.
Sustainability of Bioelectronics
What sets bioelectronics apart from traditional electronic technology isn't just the science-it's the sustainability factor. In today's electronics production, one of the biggest challenges is the increasing quantity of e-waste generated. The demand for new electronic devices, like smartphones and computers, has led to an increasing amount of e-waste that is toxic for the environment. Currently, less than 20% of e-waste is recycled globally, while the rest is often dumped in landfills, where it releases harmful toxins, like heavy metals (arsenic, chromium, cadmium and mercury) and organic compounds (polychlorinated biphenyls), into the environment.
But what if the devices we use every day could be made from materials that naturally degrade over time? By harnessing the electron-transferring capabilities of microbes, researchers are on the path to creating biodegradable circuits and self-sustaining electronic systems. This means devices could function off the grid, powered by microbial metabolism, and when they are no longer needed, they could break down into harmless components.
Bioelectronics powered by microbes could also reduce the reliance on rare and toxic materials currently used in the electronics industry, offering a green alternative for powering the future. However, this goal still needs a lot of work before it becomes practical. While cable bacteria seem to demonstrate semiconducting properties in their electrical grid, the nature of their conductive wire is still not known. Additionally, cable bacteria are still difficult to culture in the lab, and our understanding of how to fully harness their electron-transfer capabilities is still in its early stages.
On the electronics side, the main challenge is ensuring long-term operational stability of these devices, which is tricky. Scaling up these technologies is also not straightforward. However, the potential to create sustainable electronics is exciting, and interdisciplinary teams of biologists, chemists, physicists and engineers are working together to turn this vision into reality. As research progresses, we may see conductive microbial structures integrated into more complex devices. As we look to the future, the integration of biology and electronics offers a pathway toward a more sustainable world, where living organisms help power the devices of tomorrow. As these tiny microbes continue to surprise us, they may well hold the key to solving some of the biggest challenges facing modern technology.
