Our bodies are alive with electrical signals that allow us to contract muscles and sense the world. The complex brain orchestrates these processes, but it turns out that even simpler biological entities generate electricity. In a new study published in Advanced Materials, researchers reported that a bioengineered virus generated electricity when exposed to heat, a phenomenon known as pyroelectricity.1 By working with viruses, the researchers hope to better understand bioelectricity in the human body and apply this knowledge to power novel biomaterials.
The study of bioelectricity dates back to the 18th century, when Luigi Galvani discovered that electrical stimulation caused muscle contraction in frogs.2 “But still, we don't understand how this bioelectric phenomenon is actually happening at the molecular level,” said Seung-Wuk Lee, a bioengineer at the University of California, Berkeley, and coauthor of the paper.
The M13 bacteriophage, a rod-shaped virus that infects bacteria, is adorned in a molecular coat, woven from nearly 3,000 copies of a helical protein. The protein is positively charged on the inside and negatively charged on the outside, but the arrangement of the thick protein coat balances out the charges.
Over a decade ago, Lee’s research team put the squeeze on the coat proteins, which caused the bacteriophage to exhibit piezoelectricity—the ability to transform mechanical force into electricity.3 When the researchers applied pressure to the viruses, the coat proteins changed shape, breaking the charge symmetry and becoming polarized, which generated an electric field and induced a current.
In their new study, the researchers addressed whether they could similarly use heat to shift the charge and generate electricity. They edited the genetic code of the viruses to include a specific protein sequence that is attracted to nickel. This way, the viruses would bind to and stand straight up on a thin nickel-coated plate, like a city block of skyscrapers. Then, they blasted these viral cities with heat, either with fire or a laser. As the proteins melted and unfolded, the proteins’ charges became unbalanced, generating voltage. “The heat induced a polarization change, and the polarization change induced the electric potential,” Lee said.
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Although the naturally occurring helical protein produces some pyroelectricity, the researchers wanted to see if they could give the molecule some added spark. To do this, they genetically altered the bacteriophage to add a string of glutamate, a negatively charged building block of proteins, into the outside of the coat protein.1,4 When the researchers turned up the heat, the added glutamate amplified the polarization change, more than doubling the pyroelectricity of the normal protein.
“The very fact that they can genetically mutate the virus and make them pyroelectric—it's fascinating work,” said Syed Tofail, a physicist at the University of Limerick who wasn’t involved in the study.
To demonstrate the practical applications of their supercharged virus, Lee’s team generated electrical signatures that flag the presence of hazardous chemicals. To do this, they engineered the protein coat to bind xylene. Then when they heat blasted the bacteriophages, the proteins shapeshifted and produced more electricity. By detecting this difference in electricity, the authors say that the viruses could act as biosensors for harmful gases.
“Currently, the most successful application of pyroelectricity is in pyroelectric sensors,” Tofail said, adding that pyroelectric sensors are made with lead or lithium, so biological materials are appealing because they offer a more sustainable material.
While the voltage that the researchers detected by heating the viruses was small, they plan to boost the virus to power more complex electronics. Since M13 viruses self-replicate, scientists can scale up the total number of viruses, and “we can amplify the electricity in a similar way,” Lee said. “It’s a big motivation.”
- Kim H, et al. Virus-based pyroelectricity. Adv Mater. 2023;35(46):e2305503.
- Piccolino M. Luigi Galvani and animal electricity: Two centuries after the foundation of electrophysiology. Trends Neurosci. 1997;20(10):443-448.
- Lee BY, et al. Virus-based piezoelectric energy generation. Nat Nanotechnol. 2012;7(6):351-356.
- Lee JH, et al. Vertical self-assembly of polarized phage nanostructure for energy harvesting. Nano Lett. 2019;19(4):2661-2667.