Electric field measurements during plasma jet operation on/in biological samples and tissues

Many recent experiments or treatments related to biological applications of cold plasmas have been recently performed using plasma jets. It concerns either applications in vitro or in vivo. The observed effect are most of the time attributed to the very rich chemistry generated by the interaction of the rare gas plasma plume with the surrounding environment constituted either from the ambient air or this last one in complex interaction with liquids at the interface with the target (nutritious medium for in vitro experiments, organ liquids for in vivo applications). Recent experiments performed on tissue oxygenation [1] or breast cancer treatments on immunocompetent mice [2] lead to the conclusion that probably the involved chemistry could not, alone, completely allow to describe the observed phenomena. This, especially under very soft treatment conditions, was suggesting possible triggering of some immune system chain processes, but also possible modifications in the microenvironment of tissue and tumors. In this context, there is still an unknown role of the electric field associated with the ionization front or generated in the environment of the plasma plume tip. In this work, we measured the electric field in real conditions of the GREMI plasma jet applied to various biological samples (tissues and liquids), in addition to free jet conditions, using a new device (bi-component EOP Kapteos probe) that allows time (ns) and space (1 mm³) resolved measurements in two radial and longitudinal directions. We will present data obtained along the discharge capillary together with measurements along and in the plasma plume and at different level in biological samples. Both in the capillary and the plume, high longitudinal induced electric fields have been measured just ahead of the apparition of a strong radial electric field in good agreement with Kushner model results. More interesting, is the measurement of a significant electric field presence rather deep i- tissue of euthanatized animals (down to two millimeters) at levels that may affect cell permeability or behavior.