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Before you next flush the toilet, consider this: Scientists in Singapore
have developed a battery powered by urine.

Researchers at the Institute of Bioengineering and Nanotechnology
created the credit card-size battery as a disposable power source for
medical test kits.

Scientists have been scrambling to create smaller, more efficient, and
less expensive "biochips" to test for diseases such as diabetes. Until
now, however, similarly small batteries to power the devices remained
elusive.

Diagnostic test kits commonly analyze the chemical composition of a
person’s urine to detect a malady. Ki Bang Lee and his colleagues
realized that the substance being tested—urine—could also power the
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"In order to address this problem, we have designed a disposable
battery on a chip, which is activated by biofluids such as urine," Lee
wrote in an e-mail to National Geographic News.

The research team describes the battery in the current issue of the Journal of Micromechanics and Microengineering.

Daniel Kammen, director of the Renewable and Appropriate Energy
Laboratory at the University of California, Berkeley, said the
technology is a welcome innovation in a time of rising energy prices.

"All jokes [about] urine aside, what is needed are low-cost
batteries. …" he said. "The other neat thing about this is the fact
that it’s basically a biodegradable battery."

Photos: Urine sample (top) and two urine-powered batteries the size of credit cardsUrine Power

To make the battery, Lee and his colleagues soaked a piece of
paper in a solution of copper chloride and sandwiched it between strips
of magnesium and copper. This sandwich was then laminated between two
sheets of transparent plastic.

When a drop of urine is added to the paper through a slit in
the plastic, a chemical reaction takes place that produces electricity,
Lee said.

The prototype battery produced about 1.5 volts, the same as a standard
AA battery, and runs for about 90 minutes. Researchers said the power,
voltage, and lifetime of the battery can be improved by adjusting the
geometry and materials used.

Urine contains many ions (electrically charged atoms), which allows the
electricity-producing chemical reaction to take place in the urine
battery, said UC Berkeley’s Kammen. Other bodily fluids, such as tears,
blood, and semen, would work easily as well to activate the battery.

"Little bags of urine may generate chuckles," Kammen said. "But
really urine is just a nice example [of] a whole variety of compounds
that do this stuff." Even children’s lunch-box fruit-juice packets are
sufficient, he added.

Alternative Energy

While medical devices inspired the urine battery, it can activate any
electric device with low power consumption, according to Lee, the
battery’s co-inventor.

"For example, we can integrate a small cell phone and our
battery on a plastic card. This can be activated by body fluids, such
as saliva, during an emergency," he said.

According to Kammen the technology could even be applied to
laptop computers, mp3 players, televisions, and cars.
Body-fluid-powered batteries "can do all kinds of things. The issue is
how they scale up" to produce more power, he said.

One approach is to simply build larger batteries. Another method is to
link lots of little battery cells side by side, which is how the
batteries in laptop computers work, Kammen explained.

Kammen, who advocates government funding for alternative energy
research, says the wide number of applications for cheap and efficient
biofluid-powered batteries illustrates the value of research.
"Investigation leads to innovation," he said.

By John Roach