The team sandwiched a stack of postage stamp-sized sheets of viruses, which, when tapped with a finger, could generate enough electricity to power a small liquid crystal display (LCD).

Piezoelectric qualities of a virus

The scientists made the device after finding and developing a suitable virus to enhance its natural piezoelectric qualities – piezoelectric materials are materials that can build up an electrical charge when pushed or squeezed.

They used a rod-shaped virus that only infects bacteria called M13 bacteriophages. The virus replicates quickly, with one bacterium able to produce one million copies of the virus within 4 hours. In addition, the virus neatly self-assembles into stacked rows in sheets when spread on a surface.

The researchers electrified a film made with the virus and observed that helical proteins that cover the virus twist in the current. This transfer of electricity into mechanical motion within a material is the tell-tale sign that the opposite can also be true – mechanical motion can be converted into electricity.

Piezoelectric potential increased through genetic engineering

Using genetic engineering to increase the virus’s piezoelectric potential, the researchers added four extra negatively charged amino acids (called glutamates) to one end of the helical surface protein – thereby increasing the charge difference between the positively and negatively charged ends of the helix and so increasing the electrical energy it could produce when squashed.

The team stacked small sheets of the engineered virus and then sandwiched these between two gold-plated electrodes. In turn, the electrodes were connected to an LCD by wires.

When the stack is tapped with a finger, it produces up to 6 nA (nanoamperes) of current and 400 mV (millivolts) of potential. This equates to about a quarter the voltage of an AAA battery and was enough to flash the number ‘1’ on the team’s LCD display.

Device not toxic and easy to construct

The idea of piezoelectric devices is not new, and others have been demonstrated. However, the team writes that their device is unique due to its lack of toxicity and ease of construction. Existing piezoelectric devices use materials that often require toxic starting compounds, harsh conditions and/or complex procedures to develop.

Future applications

The experiment, while small scale, does raise the possibility that very useful devices could be made with the viruses that could harvest electrical energy from the vibrations all around us. One of the researchers, Dr Byung Yang Lee, writes that, within 10 years, viral piezoelectric films in your shoes could be personal electricity generators to power your iPod as you run or they could use the thumping of your heart to power a pacemaker.