Electrical and optical characterization of the plasma needle

The plasma needle is a source to create a non-thermal radiofrequency plasma at atmospheric pressure. To improve the ease of working on biological samples, a flexible plasma probe was designed. In the new configuration, the needle was confined in a plastic tube through which helium flow was supplied. The new set-up was characterized by impedance measurements and emission spectroscopy. Impedance measurements were performed by means of an adjustable matching network; the results were modelled. The discharge was found to be entirely resistive; the measured voltage was in the range 140-270V(rms) and it was in excellent agreement with model results. From the resistance, the electron density was estimated to be 1017 m(-3). Optical measurements showed substantial UV emission in the range 300 400 nm. Active oxygen radicals (O-. and OH.) were detected. Furthermore, the influence of helium flow speed was investigated. At low flow speeds, the density of molecular species in the plasma increased. UV emission and density of active species are important factors that determine the performance of plasma in the treatment of biological materials. Therefore, the new characterization will help us to understand and optimize the interactions of atmospheric plasma with cells and tissues.