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TV Plasmas Create Antimicrobial Water
Wed, 11/16/2011 - 3:49am
LISTED UNDER:
November 16, 2011
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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.
Image: Steve Graves
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Univ. 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
antimicrobial–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.
“We know plasmas will kill bacteria in water, but there
are so many other possible applications, such as sterilizing medical
instruments or enhancing wound healing,” says chemical engineer David Graves,
a professor in Semiconductor Processing at UC Berkeley. “We could come up
with a device to use in the home or in remote areas to replace bleach or
surgical antibiotics.”
Low-temperature plasmas as disinfectants are “an
extraordinary innovation with tremendous potential to improve health
treatments in developing and disaster-stricken regions,” says Phillip Denny,
chief administrative officer of UC Berkeley’s Blum Center for Developing
Economies, which helped fund Graves’ research and has a mission of addressing
the needs of the poor worldwide.
“One of the most difficult problems associated with
medical facilities in low-resource countries is infection control,” added
Graves. “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 UC Berkeley 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. Mutant strains of E. coli have caused
outbreaks of intestinal upset and even death when they have contaminated
meat, cheese and vegetables.
Based on other experiments, Graves and colleagues at the
Univ. of Maryland in College Park reported Oct. 31 at the annual meeting of
the American Vacuum Society 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.
In 2009, one of Graves’ collaborators from the Max Planck
Institute for Extraterrestrial Physics built a device capable of safely
disinfecting human skin within seconds, killing even drug-resistant bacteria.
“The field of low-temperature plasmas is booming, and this
is not just hype. It’s real!” Graves says.
In the study published this month, Graves and his UC
Berkeley colleagues showed that plasmas generated by brief sparks in air next
to a container of water turned the water about as acidic as vinegar and
created a cocktail of highly reactive, ionized molecules – molecules that
have lost one or more electrons and thus are eager to react with other
molecules. They identified the reactive molecules as hydrogen peroxide and
various nitrates and nitrites, all well-known antimicrobials. Nitrates and
nitrites have been used for millennia to cure meat, for example.
Graves was puzzled to see, however, that the water was
still antimicrobial a week later, even though the peroxide and nitrite
concentrations had dropped to nil. This indicated that some other reactive
chemical – perhaps a nitrate – remained in the water to kill microbes, he
says.
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, says 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 says. “It’s exciting to now look for ways
to apply plasmas in medicine.”
The research is supported by the U.S. Department of
Energy’s Office of Fusion Science Plasma Science Center, the UC Berkeley Blum
Center for Developing Economies, and the UC Berkeley Sustainable Products and
Solution Program.
Source: UC Berkeley
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