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Plasma needle investigations:

In 2005 we built a low-power millimeter-size atmospheric plasma jet and tested it for dental applications.

The apparatus is modeled after the "plasma needle" introduced by Eva Stoffels and her group in Holland.

Teaming with Professor David Drake of the The University of Iowa College of Dentistry, we performed tests to demonstrate that the plasma needle kills Streptococcus mutans (S. mutans) bacteria, which is the most important microorganism for causing caries (cavities).

Our first paper (1.4 MB pdf preprint):
"Disinfection of S. mutans Bacteria Using a Plasma Needle at Atmospheric Pressure," J. Goree, Bin Liu, David Drake, and E. Stoffels, submitted to IEEE Transactions on Plasma Science, 13 October 2005.

A powerpoint presentation, with color images (14.7 MB .ppt):
"Disinfection by plasma needle for dental treatment," Bin Liu, Plasma Physics Seminar, The University of Iowa, 19 September 2005.

Images from July 2005 tests :

Nozzle of the plasma needle handset. Helium gas flows from this nozzle, and radio-frequency high voltage is applied to the tungsten needle to ionize the gas. A plasma jet flows out of the nozzle and mixes with air. Radicals O and OH are formed when air molecules are dissociated. The plasma jet impinges on a surface.

We imaged the glow from the side and then used Abel inversion to reveal its internal structure. The needle is just above the center of the image, while the treated surface is horizontal, at the bottom.

Plasma treatment was performed in 501 Van Allen Hall by John Goree (left) and Bin Liu. The samples were prepared, incubated, and imaged the Dental Science Building by the group of Dr. David Drake.

Image of a 5-mm diameter plasma-treated spot on the surface of an agar plate. A light-brown color indicates living bacterial colonies, while a dark-brown color indicates dead bacteria.

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updated 13 October 2005