News in Science

Viruses to power batteries of the future

The energy for tomorrow's miniature electronic devices could come from tiny microbatteries about half the size of a human cell and built with viruses.

Researchers from the Massachusetts Institute of Technology in the US believe they can build them, thanks to a new advance in battery technology.

By pouring a mixture of the harmless, genetically engineered M13 virus and the metal cobalt over stamped silicon film, Professor Angela Belcher and her colleagues have created a flexible, microscopic battery that could be cheaply mass produced.

In theory, it could turn virtually any surface - from large computers to tiny implanted detectors for cancer or heart disease - into an energy-storing device.

"The idea of using stamping technique to produce a battery is pretty different," says Belcher. "We can make the batteries really small, which lets us put a power source on all sorts of tiny sensors."

Belcher and her colleagues created the first virus-powered battery in 2006.

Since then they have been refining their viral battery while working to create other novel energy-storing devices that could be woven into fabrics or poured into containers.

Powerful

Their most recent advance, detailed in the Proceedings of the National Academy of Science, involves stamping a base material, in this case silicon, so that the negatively charged M13 virus and positively charged cobalt can self-assemble based on their relative charges and the pattern of the stamp.

Stamping the base materials, which can theoretically be nearly any surface, means that the batteries can be produced more cheaply and efficiently. With silicon as the base material, flexible and curved batteries can be created as well.

Gram for gram, the virus-based batteries are roughly twice as powerful as traditional chemical batteries, says Belcher, although the battery cells are so small - about four micrometres across - that exact measurements are difficult. It takes about an hour for an M13 battery to form.

While one tiny cell can't hold much energy, when many cells are combined they can power real devices.

Nine months ago Belcher created a button-sized, M13-based battery and put it into her laser pointer. After numerous recharges she is still on her first virus-based battery.

"It hasn't failed yet," says Belcher.

Like her laser-pointer battery, other virus-based batteries would be rechargeable and more environmentally friendly that traditional batteries.

The virus batteries are assembled at room temperature, have a relatively neutral pH, and use smaller amounts of potentially troublesome metals like lithium or cobalt.

Applications

Because the batteries are so small they will first be used to power small things, such as lab-on-a-chip technology and implantable devices that would monitor patient health, say Belcher and other researchers.

"This technique has tremendous potential to monitor diseases like cardiovascular disease and cancer," says Assistant Professor Kimberly Kelly, an oncologist at the University of Virginia.

After chemotherapy or surgery for cancer, patients must be monitored to ensure the cancer doesn't return. In theory, a small device implanted under the skin, powered by M13, could detect proteins produced by renewed cancer cells.

In response, it could light up (literally, by triggering a small visible LED, as one example), alerting both patient and physician. It would be like a check engine light for cancer or heart attacks.

"[Belcher] is pretty close to developing this technology for light-based applications," says Kelly. "I could see them coming out in two years, five years at worst."

Eventually Belcher hopes to scale up virus-based batteries for larger devices like computers or even cars that wouldn't need a separate battery. The battery would instead be built into the surface of the car itself.

"It would be part of the manufacturing process," says Belcher. "What we do is provide the surface and the ions, and the batteries built themselves."