Engineering viruses: using biology to assemble materials, devices
MIT Professor Angela Belcher of materials science and engineering and bioengineering has an army of specially trained workers who have built—molecule by molecule—a small, flexible rechargeable battery. Her tiny, nimble workers are viruses. Mixed with certain chemicals, they develop solid coatings and stack themselves into orderly layers, creating novel materials as well as minuscule wires, coatings, and electronic devices.
The best way to make ever smaller and more powerful electronic components is to build them molecule by molecule. However, manipulating materials at the “nano-scale” (a millionth of a millimeter) to get the structure and properties you want is tricky.
But Mother Nature knows how to do it. As a graduate student, Belcher worked with the abalone and came to admire its ability to build a sturdy shell. On its surface, the animal has proteins that bind to materials in seawater, producing neatly ordered nano-scale tiles of calcium carbonate that form a surprisingly strong shell.
Abalones evolved this special ability in response to materials in their ocean environment—calcium, some iron, a bit of silica. “But what if they weren’t confined to what was within their environment as they were evolving?” Belcher said. “What if they had the whole periodic table to work with?” An organism with different proteins on its surface might work the same magic with other elements, including ones of industrial interest.
To test her idea, Belcher enlisted the help of a very simple organism—a bacteriophage. This hardy, benign virus has single-stranded DNA containing just a few genes that code for specific proteins. “With some genetic engineering, you can add DNA sequences to those genes that’ll add a little protein sequence on the virus,” said Belcher. “It’s really simple.”
The challenge is determining which genes will give the desired behavior. To find out, Belcher and her colleagues insert random DNA sequences into different viruses, put them all in solution, and test their tendency to bind to a sample material. They collect all those that bind, insert them into non-toxic bacteria that replicate millions of copies, and test them again. They repeat the process, changing conditions so that binding becomes harder and harder. “In the end, we take the winner, the one that survives, and then we clone it,” she said. “It’s sort of like having evolution happen on the time scale of a few months.”
Belcher’s team has now “trained” viruses to grow more than 40 semiconductor and electronic materials. They add precursor chemicals to a solution of selected viruses, and each virus grows a solid coating of the target material. Further tweaking has taught the coated viruses to align themselves in neat rows on a solid surface. And inserting several genes into a single virus causes it to grow multiple materials, “sewn” together without defects.
Building a battery
To create the first virus-based rechargeable battery, graduate student Kitae Nam used viruses to grow cobalt oxide on a copper surface and then added lithium on the other side. He worked at room temperature and used no toxic materials. The battery he produced looks just like Saran Wrap. It’s lightweight and flexible; its energy density is high due to its nano-scale structure; and it can be integrated into the device being powered, for example, as a coating on night-vision goggles or sewn into fabrics.
Belcher is now working with Professor Yet-Ming Chiang of materials science and engineering and Professor Paula Hammond of chemical engineering to make an even better battery. Hammond is creating a solid electrolyte from self-assembling polymers, and Belcher has developed viruses that will coat the top and bottom in monolayers to form the anode and cathode. The result: a battery that’s completely self-assembled.
Belcher’s group is already working on other energy-related technologies. They’ve built components for solar collectors—a challenge because of their large scale. And they’re beginning to think about how to make fuel cells.
In Belcher’s view, anything is possible. “I think we can apply our technologies to many other kinds of problems,” she said. Ideas include making organisms that would break down polymers to make fuels or that would incorporate carbon dioxide into their building material—a form of carbon sequestration.
Ultimately, she hopes to be able to biologically engineer the entire periodic table. “My goal is to have a DNA sequence that codes for the production of any kind of material I want,” she said. “You want a material to make some kind of object? Here’s the DNA sequence you need.”
