Biological engineer Angela Belcher is genetically modifying viruses to create batteries that can be recharged thousands of times and then decay harmlessly
Katia Moskvitch: You're making batteries using viruses—don't they normally make us sick?
Angela Belcher: When people think of viruses, the flu often comes to mind. But there are also viruses everywhere, from in the ocean to inside the gut, that infect bacteria. Those are not harmful to humans. Viruses are basically genetic material with a protein coat. They need a host so they can use its molecular machinery to make copies of themselves.
The main virus I work with has a single strand of DNA in a protein coat and it is completely benign. It only infects a particular bacterial host—and doesn't kill it, just slows it down as it uses the host to replicate itself.
KM: How did the idea to use viruses to grow materials for batteries first occur to you?
AB: I was inspired by how the abalone marine snail makes its hard shell using minimal organic material. It uses proteins to guide the incremental development of calcium carbonate in a geometric pattern. That gave me the idea to try to use biology to work with more than just the usual materials. A virus is a beautiful example of self-assembly of an ordered protein structure, and it's also easy to manipulate genetically.
KM: Why do we need new types of batteries?
AB: Most of us use rechargeable batteries in our everyday lives—in cellphones, computers, hybrid cars and more. The main type on the market are lithium-ion batteries, which require highly reactive compounds to manufacture and take an environmental toll.
As we try to increase the amount of energy that can be stored and make batteries rechargeable for more cycles, not just any material will do: we need ones that are more abundant and more environmentally friendly. As you know, you can't just throw a traditional battery away because many of the materials currently used, including cadmium and lead, can be toxic to the environment. That's why we are focusing on rechargeable bio-batteries.
KM: How do you actually make these bio-batteries?
AB: To test if it would be possible to use a virus to grow materials for electrodes, I started with a tiny virus called the M13 bacteriophage, which has a long, tubular shape.
By inserting a specific gene, we spurred the virus to produce a protein coat that binds with compounds such as cobalt oxides and iron phosphates. The virus is long and tubular, so we were able to grow nanowires with these compounds, which we used in an electrode for a prototype lithium-ion bio-battery.
KM: Once you proved it was possible, how did you improve on these bio-batteries?
AB: We improved the power performance of electrodes made from iron phosphate nanowires by finding a genetic sequence for a virus that favourably binds to carbon nanotubes (CNTs), which are highly conducting. To do this, we started with a billion different viruses and forced them to interact chemically with the CNTs – simply by mixing them in a test tube.
KM:How did you narrow it down from a billion?
AB: We selected the viruses that attached to CNTs, maybe a thousand of them, and washed the rest away. We then isolated those viruses and made copies of them by putting them into a bacterial host through infection—the normal virus-bacteria interaction. Next, we repeated the CNT-binding process with our selected viruses and chose the ones that bonded best to the CNTs.
KM: What distinguished the most useful virus?
AB: We were looking for the survival of the fittest, the one virus out of a billion that could develop a strong and specific interaction to not only coax iron phosphate nanowires to grow into a particular shape, but also to serve as a type of glue to bond those nanowires and CNTs, resulting in a more conductive composite.
Once we found the specific virus to bind the conducting material strongly, we again created copies and coated them with the nanowire compound—in this case, iron phosphate. Then we dried these composite nanowires, which incorporate iron phosphate and CNTs, and put them into a battery. The end result looks like a regular rechargeable battery, but either one or both of the electrodes are grown biologically.
KM: Can you explain the advantages of building batteries from viruses?
AB: A great thing about using viruses is that we can work with them at low temperatures, even at room temperature in some cases.
Another big advantage is that viruses are pliable. By changing the genetic code, we can make the same virus bind to different materials at once, and in this way make nanocomposites with a variety of properties. It can be really hard to control things on the nano scale, but at that level you have the advantage of being able to introduce new properties not available with larger materials.
KM: You've been making these prototypes for some time. What's the latest?
AB: A typical battery has a cathode, an anode, an electrolyte that charged ions flow through and a separator to keep the two electrodes apart. When the positively charged lithium ions move from the anode to the cathode during cell discharge, an electric current is produced.
We have recently been working on lithium-air batteries, which are powered by reactions with oxygen in the air. We have demonstrated that we can greatly improve a lithium-air battery's charge-storage capacity by using our genetically modified viruses to build nanowires to use in the battery's cathode. This is because the virus-built nanowires have a spiky surface. Compared with wires made using traditional chemical methods, our spiky ones have a bigger surface area across which the electrochemical activity happens as you use or charge a battery.
KM: How well do your different types of batteries work, compared to what's now available?
AB: Our bio-batteries are still experimental. We have been able to demonstrate really great performance but at the moment they don't have the lifetimes to compete with commercially available batteries. We can only power small devices such as flashlights, laser pointers, watches and LED lights. For devices like cars and computers, which require significantly more energy and longer usage time, we would need to improve the power performance first.
We also want to make them rechargeable for thousands of cycles. Currently, we have batteries that are rechargeable for hundreds of cycles. Our eventual aim is to use viruses to not only power our everyday electronics but also the electric cars of the future.
KM: How do you dispose of bio-batteries when they can no longer hold a charge?
AB: The ultimate goal is to make them completely biodegradable. Our batteries are already greener because the materials we use to make the electrodes, including iron or manganese-based materials, are benign to the environment, unlike many of the materials currently used, such as cadmium and lead.
KM: hat other types of problems might viruses help us to solve?
AB: Biology is very good at solving problems through selection and evolution, so there is great potential when we apply biology to problems that are not normally seen as biological problems. Why not try to use evolution to come up with new solutions?
This article originally appeared in New Scientist.
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