Investigations Of A Helium Plasma Jet In Interaction With Biological Liquids

Abstract

For the plasma medicine community it is of high interest to understand the physicochemical mechanisms concerning the effects of plasmas on living cells and cancerous cells, in particular. A first step is to study the effects produced upon biological liquids, as they represent the exchange environment for most biological process. After plasma exposure of liquids, minor changes of the basic parameters such as pH, ionic strength or chemical composition can lead to a major biological impact. Thus, this indirect effect of plasma treatment on cells behaviour must also be addressed during plasma cancer studies, together with direct exposure.

In this context, the present experiments are focused on the plasma production and transfer of oxygen and nitrogen reactive species to a liquid target, e.g. ultra pure water or phosphate-buffered saline. The plasma source consists of a helium plasma jet in a barrier discharge configuration, operated at atmospheric pressure which interacts with solutions up to 40 minutes. Electrical and optical monitoring of the plasma jet was performed over the entire exposure duration, using high speed techniques, in order to assess the plasma jet warm-up period and settling time [1], with and without liquid target. Molecular beam mass spectrometry of the jet confirmed the presence in the various negative and positive ions based on oxygen and nitrogen species [2].

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Fig. 1. Influence of elapsed time on peak values of the current (I_max), time (t_Imax) and O (777 nm) line integral intensity.

The ultraviolet absorption spectra of liquids, in the 200 - 400 nm wavelength range, were acquired immediately after exposure and they were repeated up to 14 days, in order to monitor the liquid chemistry evolution. Using spectral deconvolution, we monitored the variation of absorption bands corresponding to the following species: O₂, NO₂^-, NO₃^-, H₂O₂ and O₃. We observed an increase of the O₂ and NO₂ ^- bands, while the absorption bands related to all other species remain unchanged.