Antimicrobial activity of plasma-generated VUV radiation and its complete absorption by thin liquid layers

The atmospheric pressure argon plasma jet is a well-developed tool which is intended to be used for plasma-medical applications [1]. Therefore, plasma-generated UV and VUV radiation is of special interest with respect to medical safety because of their possible interactions with cellular compounds like DNA or proteins. [2,3]. In atmospheric air VUV-photons have a very limited range in general. However, in the case of the plasma jet the VUV-photons can come in very close vicinity of the target by the argon gas flow. Consequently, the question arises if this has any impact on medical application safety of this plasma source. Using bacteria spores in dry state on a polymer surface it could be demonstrated that the sporicidal efficacy of the argon plasma jet is mainly based on VUV action. In the case of medical applications e.g. for wound treatment contaminating microorganisms as well as cells in the tissue are usually surrounded by thin liquid layers forming its vital environment. Using a very sophisticated special analytical arrangement it could be demonstrated, that VUV <; 180 nm radiation is completely absorbed by liquid layers ≥ 100 μm. This effect was as stronger as the complexity of the liquid increased (e.g. cell culture media). However, forming of gas bubbles as a result from VUV irradiation is an indicator of liquid-changing activity of VUV. It is concluded that (a) biological effects of the argon plasma jet under wet or liquid conditions are at least partially caused by VUV-based changes of liquid composition, and (b) that direct VUV-interactions with cellular structures and resulting safety-relevant changes of cellular DNA or protein structures can be largely excluded.