The biological effect of the physical energy of plasma

Since the publication of the initial paper on atmospheric pressure plasma sterilization by Dr Laroussi in 1996, researchers have contributed to the field with an extensive number of papers on plasma medicine. However, these studies have primarily concentrated on the biological impacts of the chemical reactive components generated by plasma, specifically focusing on the effects of reactive oxygen and nitrogen species. Conversely, when plasma directly interacts with biological organisms, there are additional physical energies involved, such as electric fields, ultraviolet (UV)/vacuum ultraviolet (VUV) radiation, heat, etc., which may also play crucial roles in their interaction. This paper delves into this aspect by using the simplest bactericidal effect as a model for biological effects. Three dielectrics-Al2O3, quartz, and MgF2 glass-are employed to isolate the chemical active components, enabling the examination of the bactericidal effects of the electric field, UV, and VUV, respectively. The findings indicate that the plasma-induced electric field can induce irreversible electroporation, effectively eliminating bacteria at 27 kV cm-1. Notably, at a plasma-induced electric field of 40 kV cm-1, sterilization efficiency experiences a significant enhancement. The bactericidal effects of UV and VUV are closely linked to the choice of the plasma's working gas. Specifically, when Ar is the working gas, the bactericidal effect of UV surpasses that of using only the plasma-induced electric field by two orders of magnitude, while using He results in only a one-order increase. Despite VUV radiation being considerably weaker than UV, its bactericidal effect remains substantial. In instances where He plasma is utilized, the addition of VUV doubles the bactericidal effect. In short, this paper pioneers the exploration of the biological effects of plasma's physical energy, providing essential insights for the advancement of plasma medicine.