Technology
Plasma Sterilization
By Hope Cristol
Move over, autoclave. Step
aside, toxic chemicals. There's a new type of sterilization so effective and versatile
that it can kill bacteria on everything from food packaging to spacecraft.
Plasma sterilization, developed by researchers at Old Dominion
University in Norfolk, Virginia, and the University of California in San Diego, may even
have applications in decontaminating biological warfare agents.
Plasma, a collection of electrically charged particles and non-charged
particles, is sometimes called the fourth state of matter. Just as heat turns water (a
liquid) into steam (a gas), heat can turn steam into plasma. Thus, most plasma is
thousands of degrees centigrade and impractical for daily use.
However, the Old Dominion and University of California researchers
created a "cold" plasma that can sterilize at room temperature and pressure.
They tested it on two types of bacteria: One was spore-forming, similar to anthrax but not
dangerous; the other was E. coli, a non-spore-forming bacteria that causes food poisoning.
Both types of bacteria were killed after being exposed to the cold
plasma--which is particularly significant because the bacterial spores are much harder to
kill than normal bacterial cells.
To produce the cold plasma--a form of plasma that was first created in
the 1990s--the researchers spaced two flat electrodes about five centimeters apart. Then
they injected the gap with 97% helium and 3% oxyhen. Finally, they supplied the electrodes
with 50 to 300 watts of electricity--less than what many food processors use.
The result: plasma that's cheaper and easier to use than other plasmas
because it works at room temperature and pressure and uses little power.
Old Dominion researcher Mounir Laroussi has high hopes for it. "The
use of cold plasma to sterilize heat-sensitive reusable medical tools in a rapid, safe,
and effective way is bound to replace the present method, which uses a toxic gas," he
says. "Plasma is also being seriously considered for the decontamination of
biological warfare agents."
Source: Institute of Physics, 76 Portland Place, London W1B 1NT, United
Kingdom. Web site: www.iop.org.
