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SPIE Professional January 2012

Ionized plasmas as cheap sterilizers for the developing world

PHOTONICS FOR A BETTER WORLD

University of California, Berkeley scientists have shown that ionized plasmas like those in neon lights and plasma TVs not only can sterilize water, but make it able to kill bacteria for as long as a week after treatment.

Devices able to produce such plasmas are cheap, which means they could be life-savers in developing countries, disaster areas, or on the battlefield where sterile water for medical use — whether delivering babies or major surgery — is in short supply and expensive to produce.

"One of the most difficult problems associated with medical facilities in low-resource countries is infection control," said David Graves, chemical engineer at UC Berkeley. "It is estimated that infections in these countries are a factor of three-to-five times more widespread than in the developed world."

Graves and his colleagues published a paper in the November issue of the Journal of Physics D: Applied Physics, reporting that water treated with plasma killed essentially all the E. coli bacteria dumped in within a few hours of treatment and still killed 99.9 percent of bacteria added after it sat for seven days.


A brief spark in air produces a low-temperature plasma of partially ionized and dissociated oxygen and nitrogen that will diffuse into nearby liquids or skin, where they can kill microbes similar to the way some drugs and immune cells kill microbes by generating similar or identical reactive chemicals.
(Courtesy of Steve Graves)

Based on other experiments, Graves and colleagues at the University of Maryland in College Park reported at the annual meeting of the American Vacuum Society in October that plasma can also "kill" dangerous proteins and lipids — including prions, the infectious agents that cause mad cow disease — that standard sterilization processes leave behind.

Plasma discharges have been used since the late 1800s to generate ozone for water purification, and some hospitals use low-pressure plasmas to generate hydrogen peroxide to decontaminate surgical instruments. Plasma devices also are used as surgical instruments to remove tissue or coagulate blood. Only recently, however, have low-temperature plasmas been used as disinfectants and for direct medical therapy, said Graves, who recently focused on medical applications of plasmas after working for more than 20 years on low-temperature plasmas of the kind used to etch semiconductors.

"I'm a chemical engineer who applies physics and chemistry to understanding plasmas," Graves said. "It's exciting to now look for ways to apply plasmas in medicine."

-Source: UC Berkeley News Center


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DOI: 10.1117/2.4201201.09

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