M13 viruses emerging from an E. Coli bacteria.  (Source: Profimedia)
Viruses act as tiny piezoelectric generators

Viruses, tiny chunks of protein and nucleic acid, have long plagued mankind and its evolutionary ancestors before it.  But thanks to the wonders of modern genetic engineering, researchers believe they have finally been able to instill a beneficial purpose in these deadly pests.

I. From Pest to Power

A team of researchers at Lawrence Berkeley National Laboratory -- one of 16 U.S. Department of Energy (DOE) national laboratories -- has created a special breed of virus that undergoes self-nanoassembly to form tiny piezoelectric generators -- machines which harvest mechanical energy (vibrations or pressure) to directly produce electricity.

The special "bug" is the M13 bacteriophage, a rod-shaped virus that only infects bacteria (such as E. coli bacteria) -- not humans.

Faculty researchers Seung-Wuk Lee, Ramamoorthy Ramesh, and Byung Yang Lee selected the virus due to its tendency to self-assemble into nanofilms, given its rod-like shape.  The viruses tightly pack "like chopsticks in a box" and are easy to grow by the millions given a small supply of host bacteria.

Bacteriophage research team
The team responsible for the virus generator includes Byung Yang Lee, Seung-Wuk Lee, and Ramamoorthy Ramesh (from left to right). [Image Source: Roy Kaltschmidt of Berkeley Lab]

Professor Ramesh, a professor of engineering and physics at the University of California Berkeley carried out tests on the virus films to see if the viruses' nanostructure was piezoelectric.  Sure enough, when exposed to an electric field, the helical proteins coating the virus's genetic material twisted and turned -- a sure sign that the film was piezoelectric.

II. Refining the Virus

But the effect was too weak to be of use.  So the researchers spliced a quadruplet of negatively charged amino acids into one of the coat proteins.  The results was a larger voltage gradient across the coat.  The researchers also tested stacking films of the modifed viruses to see how thick they could layer the viruses in order to get the maximum effect.

M13 Bacteriophage
A peek at the modified coat protein (left) and an atomic force microscopy image of the virus nanofilm (right). [Image Source: Roy Kaltschmidt of Berkeley Lab]

The best results were observed using 20 of the virus nanofilms.  Using spontaneous assembly, the researchers created a 1 cm2 multi-nanofilm with gold electrodes on either side.

When pressure was applied to the film a 400 millivolt, 6 nanoampere current was put off.  That's about a quarter of the voltage of an AAA battery, albeit at a far smaller current.  Still it was enough to power a '1' to show up on a low-power liquid crystal display.

Virus generator
Pressing the virus multifilm powers an LCD. [Image Source: Roy Kaltschmidt of Berkeley Lab]

III. Great Expectations

The development is an exciting one for the field of piezoelectrics, which relies on a phenomena first described a century and three decades ago.  While the piezoelectric effect is a crucial part of electric cigarette lighters and scanning probe microscopes, typical piezoelectrics rely on toxic materials.

By contrast, the virus piezoelectric films are nontoxic and nonreactive.  The researchers imagine the self-assembing nanofilms to one-day become an integral part of clothing, producing power to recharge mobile electronics from common activities such as walking, lifting objects, or typing.  The generator could also be used in medical nanobots.

In the meantime, the team is busy working to refine their proof of concept design, by further tweaking the viruses' genetics to produce more current and voltage.  Professor Lee comments, "We're now working on ways to improve on this proof-of-principle demonstration.  Because the tools of biotechnology enable large-scale production of genetically modified viruses, piezoelectric materials based on viruses could offer a simple route to novel microelectronics in the future."

The team's work has been published [abstract] in the prestigious peer-reviewed journal Nature Nanotechnology.

The work was funded by the National Science Foundation and DOE funding.

Source: Lawrence Berkeley National Lab

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