Thousands of the virus-based electrodes created a power-pack array about 1 centimetre across. Credit: Nam et al/PNAS

A virus has helped to create a new type of tiny battery, made with a simple stamping technique, that could power miniature devices.

Electronic devices used for controlled drug delivery, or to power tiny lab-on-a-chip applications, need to get their power from somewhere. But as conventional batteries are made smaller and smaller, they contain less and less of the materials that actually store charge, causing a decline in efficiency.

Using nanoscale components can boost a battery's capacity to store charge. Now, scientists at the Massachusetts Institute of Technology, Cambridge, have designed a quick method to build a microbattery that relies on a genetically-engineered virus called M13.

The scientists first made a template from polydimethylsiloxane (PDMS), a commonly used silicon-based organic polymer. After coating it with alternating layers of positive and negative electrolytes, they added the virus.

The virus had been designed to have negatively charged amino acids at its surface, so that it stuck to the template, and an affinity for cobalt — a favoured material for batteries. Each virus is a semi-rigid fibre a few nanometres in diameter and about a micrometre long, which tends to pack tightly into a whorl that looks similar to a fingerprint.

Scanning electron microscope image of the microbattery electrodes. Each whorl is about 4 micrometres across. Credit: Nam et al / PNAS

The whole assembly was dipped into a solution of cobalt ions, which coated the viruses to create a very large surface area that could store charge. Stamping the template onto a platinum layer and peeling off the PDMS left behind an array of small dots of the prepared material, cobalt-side down, which formed the heart of an effective battery. The work is published in the Proceedings of the National Academy of Sciences1.

"This is the first time anyone has ever stamped a battery device," says Paula Hammond, part of the MIT team.

It's also an elegant demonstration of the potential use of viruses for making nanodevices, says Jan van Hest from the Nijmegen Centre for Molecular Life Sciences, the Netherlands. But he wonders if the addition of viruses could actually be overengineering the system. "Using viruses as a template introduces an extra non-active layer, which lowers the percentage of active material," van Hest says. He suggests that cobalt oxide nanoparticles could work just as efficiently.

But the process is certainly an improvement on current technologies, says Hammond, "We're talking about a simple, inexpensive and environmentally better way of generating a microbattery," she says. She hopes to extend the design so that the second electrode necessary for a complete battery can also be stamped using the same process.