Using viruses to assemble inorganic materials has several advantages, says Daniel Morse, professor of molecular genetics and biochemistry at the University of California, Santa Barbara. First, the placement of the proteins, and the cobalt and gold that bind to them, is precise. The virus can also reproduce quickly, providing plenty of starting material, suggesting that this is manufacturing technique that could quickly scale up. And this assembly method does not require the costly processes now used to make battery materials.
“You could do this at the industrial level really quickly,” says Brent Iverson, professor of organic chemistry and biochemistry at the University of Texas at Austin. “I can’t imagine a way to template or scaffold nanoparticles any cheaper.”
Yet-Ming Chiang, materials science and engineering professor at MIT and one of Belcher’s collaborators, says that, while small batteries designed for specific applications could be made using this process within a couple of years, much work remains to be done. For example, cobalt oxide might not be the best material, so the researchers will be engineering viruses to bind to other materials.
One of the ways they have done this in the past is using a process called “directed evolution.” They combine collections of viruses with millions of random variations in a vial containing a piece of the material they want the virus to bind to. Some of the viruses happen to have proteins that bind to the material. Isolating these viruses is a simple process of washing off the piece of material –only those viruses bound to the material remain. These can then be allowed to reproduce. After a few rounds of binding and washing, only viruses with the highest affinity for the material remain.
The researchers also want to make viruses that assemble the negative electrode as well. They would then grow the positive and negative electrodes on opposite sides of a self-assembling polymer electrolyte developed by Paula Hammond*, another major contributor to the project. This would create self-assembled batteries, not just electrodes. Another goal is to make “interdigitated” batteries in which negative and positive electrode materials alternate, like the tines of two combs pushed together – this could pack in more energy and lead to batteries that deliver that energy in more powerful bursts.
And batteries could be just the beginning. Since the viruses have different proteins at different locations – one protein in the center and others at the ends – the researchers can create viruses that bind to one material in the middle and different materials on the ends. Already, Belcher’s group has produced viruses that coat themselves with semiconductors and then attach themselves at the ends to gold electrodes, which could lead to working transistors.
“If you can make batteries that truly are effective this way, it’s just mind-boggling what the applications could be,” Iverson says.
*Correction: The virus-battery work was the result of a collaboration between researchers at MIT. The original article mentions Angela Belcher and Yet-Ming Chiang. An important part of this work was the development of a self-assembling polymer electrolyte by Paula Hammond, MIT chemical engineering professor.
Home page image courtesy of Angela Belcher, MIT.