Minature Light Saber is Tough on Germs
Mounir Laroussi Invents a Handy Cold Plasma Device

By Jim Raper

Most of the electronic instruments in the laboratory of Old Dominion University researcher Mounir Laroussi are gangling and custom-rigged to accomplish mind-boggling tasks.
But the homemade device that is his latest claim to fame is a plain-looking cylinder about the size of an electric toothbrush.

He sometimes calls it the plume. Others called it a miniature light saber. The name that seems to have gained the most traction, however, is simply “pencil,” as in plasma pencil.

After Laroussi went public with his invention of the pencil in the summer of 2005, the device’s ability to kill germs without harming healthy human tissue was noted in several scientific publications, as well as in the February 2006 issue of National Geographic magazine. Representatives of private industry from the United States, the United Kingdom, France and Switzerland have made contact with him—and several have visited Norfolk—to inquire about commercial rights to the pencil.

“The interest pleases me,” he says, “and I am pleased by how far our small plasma community has come.” During the past decade he has been a leader in the development of the so-called “cold” plasma, and of the use of plasma technology in biomedical applications. Nevertheless, like any pioneer, he has had some moments of frustration and uncertainty during his quest to turn an original idea into marketable products.

When Laroussi was growing up and beginning his education in his native Tunisia, the only plasma he knew about was blood plasma. During his doctoral education and postdoctoral work in electrical engineering at the University of Tennessee, however, an altogether different plasma grabbed his attention. This type of plasma is a soupy cloud created when some sort of energy, such as extremely high heat, rips electrons away from the nuclei of atoms.

Think of H2O energized so that it progresses from ice to water to steam, and, finally, to plasma, which some scientists call the fourth state of matter. Plasma can emit light of different colors and conduct electricity. The sun is mostly a superheated plasma and so is lightning. Neon gas contained between electrodes produces plasma that lights up the lettering and logos of neon signs. A field of plasma cells glows in precise colors to create images on plasma television sets. Jets of plasma can etch silicon chips, or can treat surfaces of potato chip packages so that ink or paint sticks more readily to them.

Cold plasma proves useful
Laroussi’s “plasma-heating” experiments at the University of Tennessee in the early 1990s were in support of attempts to create energy by fusion—in a manner similar to how the sun produces heat and light. He also studied ways to change surface properties of polymers. These initial experiments involved plasmas activated inside a vacuum chamber, because at normal atmospheric pressure the plasmas are too hot and aggressive to use.

“But, doing everything under vacuum is very tedious, and we wanted to move outside the vacuum chamber and into normal pressure,” he said. By trial and error, including the use of ultrafast pulses of electricity, Laroussi was able to turn gases at normal atmospheric pressure into “cold” plasmas. He quickly moved to the head of the class in his field of research, and became known for his ability to produce an abundant amount of cold plasma economically.

In cold plasma, electrons are wildly excited but they are so light in weight that they produce little heat. Heavier ions in this particular soup are relatively unexcited and so they also produce very little heat. Although much less aggressive than conventional plasmas, the cold plasma that was the subject of Laroussi’s research retained enough potency for many industrial tasks, while having a significant ease-of-use advantage over conventional plasma.

“Then one evening I was home, and probably bored, and I began to wonder what I could do with plasma next,” Laroussi says. “I started thinking about treating surfaces, not in order to affect the surfaces, but to affect the biological materials that may be on the surfaces. I guessed that the plasma would have an effect on cells. That was 1994.”

The very next year he presented his first research paper on the capabilities of plasma to kill bacteria, as might be used in sterilizing medical instruments. (Sterilizing with heat can ruin delicate instruments and chemical disinfection can leave problematic residues.) “I wanted very much to publish my findings, but I worried that the editors of a plasma journal may not accept a paper that mixed plasma findings and biological findings. They might ask, ‘What do the two things have to do with one another?’ ”

Nevertheless, he got the paper published in the Institute of Electrical and Electronics Engineers’ journal, Transactions on Plasma Science, and then set his sights on slipping the topic of biological applications of plasmas into one session or another of the IEEE’s annual International Conference on Plasma Science.

“The problem was, these sessions were set up rather rigidly and biological applications research was so new,” he says. Laroussi finally worked out an agreement with a colleague who ran a session on microwave-plasma interaction. “He would break his session into two and let me be chair of one half of it,” Laroussi says. “That was 1998. I remember well, the conference was in Raleigh, N.C. We looked all over and found only three papers on biological applications. So much has changed since then. We have gone from having to sneak half of a session into the program to having the biological applications session be the largest or among the two largest each year at the conference. Today every international conference on plasma science includes a session on biomedical applications.”

Also during the closing years of the 1990s, Laroussi set up what has been a lasting funding relationship. Many research funding agencies, he says, “were a little skeptical” of biological applications of plasmas, “but the one who really believed in its potential was the Air Force.” He describes Robert Barker, the program manager for plasma physics at the Air Force Office of Scientific Research, as a “visionary.”

From Tennessee to Norfolk
The year 1998 was important for Laroussi for another reason; that was when he decided to come to Old Dominion. The person most responsible for luring him to Norfolk was Karl Schoenbach, eminent scholar and professor of electrical engineering at ODU’s Frank Batten College of Engineering and Technology. By 1998, Schoenbach had built a sturdy reputation in bioelectrics research. “He encouraged me to come to ODU because we are going to try to form a center devoted to bio-inspired research,” Laroussi says.

The Frank Reidy Research Center for Bioelectrics did come to pass in 2003 as a collaborative endeavor of ODU’s Batten College and Eastern Virginia Medical School. The facility is located four miles from the ODU campus in the City of Norfolk Public Health Building. Schoenbach, who now is the Batten Chair in Bioelectrics Engineering, is director of the center.

Even before the center opened, however, in 2001, Business Week magazine named Laroussi and Schoenbach as experts in the new field of cold plasmas, and both men had begun to create a stir internationally with their research involving electrical-pulse and plasma treatments related to medicine. (See companion story about research of Schoenbach and others at the Reidy Center that uses pulsed electric fields to kill cancer cells.)

“Mounir Laroussi is a real asset to our center,” Schoenbach says. “The plasma pencil has a Star Wars aspect as a space-age lifesaver, but his work with large plasmas is very well suited to bacterial decontamination and is equally impressive.”

Laroussi’s reputation as a researcher has been enhanced by his knack for mechanical tinkering. During his development of the plasma pencil he invented a new type of ultraviolet lamp and he has built several other devices that apply plasma technology; he holds four patents in the field. But his main quest was to build a plasma pencil that shot out an external, cold plasma plume. Such a device would be much more user friendly than early cold plasma generators, which created a cloud of plasma between two electrodes that were no more than a couple of inches apart. “We needed to get the plume out where we could access it,” he explains.

While he was working on his ideas, other researchers produced devices smaller than a breadbox that could shoot out plasma plumes less than a half-inch or so. But these devices tended to be hotter, unwieldy, unpredictable and unsuited to prolonged use because of overheating. Laroussi wanted true portability, he wanted a genuinely cold plume that could be tuned to lengths between 1 inch to 2 inches, and he wanted reliable usage for up to eight hours at a time.

“I always go back to the saying of Thomas Edison,” Laroussi says. “He said that invention is 1 percent inspiration and 99 percent perspiration. That is the way it was with the plasma pencil. Edison was 100 percent right. We tried many ideas, changing materials and et cetera, day in and day out, and finally one day we hit everything right.”

Xin Pei Lu, a postdoctoral researcher at the Reidy Center, assisted Laroussi during the testing of the various versions of the device.

Right out of the chute last summer, the pencil was lauded in scientific publications and other national media for its potential uses, including killing plaque- or infection-causing bacteria in the mouth, disinfecting wounds and sterilizing tools.

More research is needed
Follow-up research in early 2006 supported predictions that the pencil could be useful to dental and medical professionals. Together with Wayne Hynes, ODU associate professor of biological sciences, and Gayle McCombs, ODU associate professor and director of the Dental Hygiene Research Center of the Gene W. Hirschfeld School of Dental Hygiene, Laroussi’s research group did extensive tests of the plume’s effect on various organisms under various sets of conditions.

“We have seen that the pencil is able to affect the growth of a number of different organisms, including some spore-forming organisms,” Hynes says. “When bacteria are spread on the surface of a nutrient media and then exposed to the pencil plasma plume, the growth of some bacteria are inhibited. We are currently expanding our screening to determine what organisms are inhibited by the plasma, and trying to determine the conditions needed to inhibit growth of different organisms.”

Hynes, whose comments about the research were made in spring 2006, believes that the pencil has potential to be used by dental professionals to treat bacterial infections of the mouth. “A number of conditions still need to be sorted out before we can predict if that is going to be the case, but it seems possible.”

Adds McCombs: “It is our hope that the cold plasma research will ultimately lead to technology that can be used in dentistry as a cost-effective, efficient way to reduce or eliminate oral and environmental pathogens that cause disease.” 

Another round of research just under way in spring 2006 pairs Laroussi with Fred Dobbs, ODU professor of ocean, earth and atmospheric sciences, whose primary expertise is in marine microbial ecology. A grant from the Air Force will allow the researchers to learn more about how cold plasma impacts complex eukaryotic cells such as mammalian cells.

Every time Laroussi passes his hand in a slow sweep through the plume of the plasma pencil he illustrates what seems to be an important characteristic of the device: although a brief burst of cold plasma plume can zap various types of simple prokaryotic cells (such as bacteria), the same burst tends to have no significant effect on the complex eukaryotic cells that make up human tissue. Through these latest experiments, Laroussi and Dobbs hope to provide more evidence of the pencil’s ability to kill bacteria inside the mouth or in an open wound without damaging healthy tissue.

The researchers also want to obtain data that will indicate whether cold plasma treatments can be devised to attack certain eukaryotic cells—such as cancer cells—or to remove dead tissue and accelerate healing.

Laroussi says other studies have shown that eukaryotic cells are protected from a plasma assault because their DNA and other essential components are protected by inner membranes. Prokaryotic cells, however, have only outer membranes and free-floating DNA. He theorizes that the upcoming experiments by him and Dobbs will show that the jet of the pencil can blow out the outer membranes of prokaryotic cells and cause internal damage that is not so easily accomplished with eukaryotic cells. (The pencil’s jet is produced from a neutral helium medium, but is peppered with highly reactive oxygen atoms that can kill prokaryotic cells.)

Zohir Handy, the ODU licensing manager in the Office of Research, calls the pencil “a sexy appliance that is getting a lot of attention from industry,” and says that any studies showing its safety and the extent of its usefulness in medicine and dentistry will make it even more attractive for commercial development.