Hot Prospects for Cold Plasma

During the Persian Gulf War in 1991, the Pentagon feared that a desperate Saddam Hussein would unleash biological weapons on U.S. soldiers. Although that threat never materialized, the U.S. military decided after the war that the conventional method of decontaminating tanks and rifles -- a dousing with water and bleach solutions -- was insufficient. Decontamination of infected soldiers was even more problematic.

The result was a Pentagon-funded research effort to focus on a technology called cold plasma. No, not the plasma found in human blood. This plasma is actually a fourth state of matter, a soup of positively and negatively charged atomic particles and molecules. A bluish substance that resembles a foglike gas, cold plasma can destroy the deadliest microbes lodged on the skin, weapons, or clothes. Yet despite its deleterious effects on bacteria, scientists believe this treatment won't burn skin -- you'd only feel a tingle -- or damage materials such as plastic or steel.

Beyond these military applications, scientists now foresee much broader civilian uses for the technology. They envision that cold plasma could be used to sterilize fragile, plastic medical instruments that are destroyed by heat sterilization. Another application with even greater business potential would be using cold plasma to ensure that foods are free of dangerous Salmonella bacteria or to create food packaging that resists microbe growth. Barely out of research stages, these new biological uses could be tried out by some of the food or medical industry giants within a year, predicts Karl Schoenbach, a cold plasma expert at the Old Dominion University (ODU).

THE STUFF OF STARS. Although the substance may sound exotic, plasma is actually quite common, making up some 99% of the known universe. It can be found in the sun, the stars, and bolts of lightning. Humans have learned to control plasma through electric and magnetic fields. Welders have long used searing-hot plasmas to weld metals.

But plasma comes in two basic types -- hot and cold. The latter kind has already found uses in a variety of manufacturing processes. For example, flat-screen televisions use cold plasma to radiate light and create images. Consumer-products companies use cold plasma in the processes that apply coatings to make diapers water-resistant, strengthen beer bottles, and make lettering stick to the plastic surface of potato chip bags. Most important, cold plasma is used to finely etch channels on integrated circuits -- the chips inside our desktop and laptop computers that made the Computer and Internet Age possible.

Only recently did scientists decide to try out biological applications for cold plasma. Their research showed that plasma can break down complex chemicals found in nerve gases and deadly biological agents like anthrax. Plasma can decontaminate in minutes what might require hours of work with standard methods. And anthrax can live in soil for years, so long-term decontamination could prove crucial should a biological war ever occur. "It's very exciting, especially if you look at the alternative of dousing people with chlorine bleach," says Robert Barker, program manager for plasma physics at the Air Force's Office of Scientific Research.

BROAD IMPACT. The plasma dividend could be huge, considering the meager research tab. Over the past five years, the Air Force and other grantors have invested about $1 million per year into biological cold plasma research. Interest from commercial sector is likely to bring in much larger sums, says Gerald Rogoff, chairman of the Coalition for Plasma Science. And recently developed cold-plasma applications could have as much impact on other industries as cold plasma has had on chipmaking, says Joseph Cecchi, dean of the school of engineering at the University of New Mexico.

Cold plasma has been used in semiconductor manufacturing for at least 15 years. It is used in 40% of the steps used to make semiconductors, says Noah Hershkowitz, director of the Center for Plasma Aided Manufacturing. And cold-plasma equipment accounts for a large chunk of the chipmaking-equipment market. That market clocked $17.6 billion of sales in 1999 but is projected to reach $33 billion by 2004, according to semiconductor-equipment manufacturer Applied Materials Inc.

"We are incredibly dependent on [cold plasma processes]," says Joe Mogab, director of advanced process development and external research for Motorola's semiconductors products. At Motorola, cold-plasma processes account for about 35% of circuit-manufacturing costs.

SOME BIG IFS. Still, the various newer applications of cold plasma could outstrip semiconductors in terms of dollars spent on cold plasma in the near future. That's because health-care costs are expected to grow worldwide, and the use of alternative technologies to kill germs could come to the fore as more resistant strains of bacteria emerge. The food industry is expected to become as big or even bigger a user of cold-plasma processes.

But to reach such widespread use, researchers have several hurdles to overcome. Scientists everywhere -- from Stanford and Princeton universities to ODU -- are searching for ways to make cold-plasma generation more cost-effective by lowering the amount of power these processes consume. Currently, making one cubic meter of low-density cold plasma requires between 30 megawatts to 100 megawatts of energy, Barker says. Even though most uses require far less than one cubic meter, the power intensity of cold-plasma generation makes it cost-prohibitive.

"Everybody wants them right now, but nobody is willing to pay the money," says Joe Birmingham, vice-president for research and development at Meso Systems Technology, a company that's developing commercial applications for cold plasma. Yet, "I think it's going to happen in spite of cost," he says, citing the economic benefits of using plasma for otherwise messy or costly treatments.

TINGLY FEELING. Another challenge is to prove that cold plasma is safe for direct human exposure. Igor Alexeff, a professor emeritus at the University of Tennessee, Knoxville, and a pioneer in the field, says he put his hand in a small field of cold plasma and felt nothing but a tingling sensation. His skin was not damaged. Alexeff and others are fairly certain that cold plasma will prove safe. But those opinions are still a long way off from a full-fledged U.S. Food & Drug Administration approval.

In spite of these challenges, many of the researchers involved in these projects remain confident. "This technology works already and works in [an] extremely effective fashion," Barker says. The field continues to attract talent from the research community, and commercial interest has grown, too. Grants from business for work in cold plasma are expected in 2001, and more graduate students are entering the field. "It may be cold plasma, but it's really a hot field," says Mounir Laroussi, a plasma researcher in the Department of Electrical & Computer Engineering at ODU.

It remains to be seen whether or not cold plasma can catch fire in the consumer arena, but a blue fog may be coming to a hospital near you in the not-so-distant future. By Olga Kharif in New York

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