Plasma pencil kills germs
thoughts site


Plasma pencil kills germs

Posted by archive 
The wand developed by an ODU professor looks like a flame, but it isn't hot. Scientists have so far used it to kill E. coli.

October 7, 2005

NORFOLK -- Physicist Mounir Laroussi walks quickly through the gray, empty space that greets him when the elevators open to the Frank Reidy Research Center for Bioelectrics on Southampton Avenue.

He enters a hall and unlocks a wooden door to his lab. On a worktable lies a small, plastic wand that you might not have noticed in the midst of tall metal helium tanks, computers and assorted machines.

But the wand is the most interesting thing in the room.

Laroussi calls it the "plasma pencil." Plasma is a substance made of energized atomic particles that's created when gas is electrified. It's considered the fourth state of matter besides solids, liquids and gases.

The pencil generates a "cold plasma," which can be used to kill germs that contaminate surfaces, infect wounds and rot your teeth. In the future, it might be used to destroy tumors without damaging surrounding tissue. Laroussi, an associate professor at Old Dominion University, hopes the beam will soon find its way into doctors' and dentists' offices.

When he turns the pencil on, it blows a high pitched whistle as a glowing, blue-violet beam about 2 inches long instantly appears at one end. Stick your finger in its path and you only feel a cool breeze, but the beam is powerful enough to blast apart bacteria that's crawling on your skin.

It's like a mini blowtorch without the heat.

In nature, plasma can be extremely hot and difficult to control. Solar flares and lightening bolts are a form of plasma. So are the Northern Lights.

Plasmas are made when energy splits bonds between atoms in the air, sending atomic particles flying like balls on a pool table. That activity can release massive amounts of heat.

But cold plasmas are different.

"The electrons are your agents," Laroussi said. "You put energy in them and they do the chemistry for you."

Since electrons are unimaginably light and move quickly, they don't emit heat the way heavier particles do. Thus, to make cold plasma, you energize the electrons and not the heavier, heat generating particles. Cold plasmas can be room temperature or heat up higher than 134 degrees Celsius (273 F). But the plasma pencil's plume is just 34 degrees Celsius (75 F), which is about room temperature.

"I have been dreaming of a device like this," Laroussi said. "Inside it's mostly empty. There's nothing to it."

Perhaps that's a bit modest. After all, no one else has a device like this.

Laroussi, a native of Tunisia in Northern Africa, developed an interest in cold plasmas while working on his electrical engineering doctorate at the University of Tennessee. The Air Force Office of Scientific Research provided him with $500,000 in grants over the years for his research in cold plasmas. The pencil, developed with the help of colleague Xinpei Lu, is one device to emerge from that work.

Normally, scientists use big, metal vacuum chambers to create tiny blobs of plasma between two electrified plates. You couldn't open the machine or touch the plasma. The machines also cost up to $20,000 or more and used a lot of power.

The plasma pencil is made of inexpensive material and uses less than three watts of electricity.

It uses a stream of helium gas laced with oxygen that is blown between two copper electrodes. Electricity pulses through the electrodes thousand of times in a second to split the oxygen molecules into single oxygen atoms.

The atoms, called radicals, are extremely reactive. They attack the cell walls of bacteria, tearing them open or boring holes through them. Bacteria's internal contents spill out and the organisms die.

So far, the researchers have only used the pencil to kill E. coli bacteria in a petri dish. Wayne Hynes, ODU associate professor of Biological Sciences, is helping Laroussi test the pencil for dental uses. Unfortunately, it won't replace the sharp tools that scrape plaque off the teeth, but it could sterilize dental equipment or kill bacteria that cause gum disease. He cautions that it's still very early in the research.

Laroussi and his team are working on the device to make the plume bigger and longer and the pencil smaller. It takes a lot of complex math, physics and geometry.

Laroussi said anything is possible. Rather than using harsh, noxious chemicals to clean medical equipment or mop up bioterror agents, we could use plasma plumes of various sizes and strengths to kill the contaminants without damaging surfaces or ruining expensive equipment.