The plasma pencil is a dielectric tube where two disk-shaped electrodes of about the same diameter as the tube are inserted, and are separated by a small gap. Each of the two electrodes is made of a thin copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 ring attached to the surface of a centrally perforated dielectric

Dielectric

A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...

 disk. The plasma

Plasma (physics)

In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

 is ignited when nanoseconds-wide high voltage pulses at kHz repetition rate are applied between the two electrodes and a gas mixture (such as helium

Helium

Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

 and oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

) is flown through the holes of the electrodes. When a plasma is ignited in the gap between the electrodes, a plasma plume reaching lengths up to 12 cm is launched through the aperture of the outer electrode and into the surrounding room air. The cold plasma plume emitted by the plasma pencil can be used to kill bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 without harming skin tissue.

Applications of the plasma pencil are in wound

Wound

A wound is a type of injury in which skin is torn, cut or punctured , or where blunt force trauma causes a contusion . In pathology, it specifically refers to a sharp injury which damages the dermis of the skin.-Open:...

 healing, killing of oral bacteria, and in controlled surface modification of heat-sensitive materials. The plasma pencil was invented by Mounir Laroussi

Mounir Laroussi

Mounir Laroussi, is a Tunisian-American scientist. He is known for his work in plasma science, especially low temperature plasmas and their biomedical applications.Early Life...

, a plasma science professor at Old Dominion University, Norfolk, VA, USA.

Sources

• M. Laroussi and X. Lu, “Room Temperature Atmospheric Pressure Plasma Plume for Biomedical Applications”, Applied Physics Letters, Vol. 87, 2005.

• M. Laroussi, C. Tendero, X. Lu, S. Alla, and W. L. Hynes, “Inactivation of bacteria by the Plasma Pencil”, Plasma Proc. Polym.3, pp. 470–473, 2006.

External Links

• http://abcnews.go.com/health/ColdandFluNews/story?id=5987227&page=7
• www.nature.com/news/2005/050919/full/news050919-13.html