Evolution of Electrical and Optical Parameters of a Helium Plasma Jet in Interaction With Liquids

A helium-operated atmospheric pressure plasma jet was used to treat biologically relevant liquids, such as ultrapure water and phosphate-buffered saline. The present experiments are focused on the behavior and evolution of selected electrical and optical signals of the helium plasma jet, while in contact with the liquid targets. To that extent, this article presents multiple results extracted from the monitoring of the electrical current over the entire treatment duration, with emphasis on the identification of a minute order long plasma warm-up duration and the differences observed when using the two liquid targets. Moreover, spectral monitoring of the intensity of lines and bands corresponding to helium, oxygen, and nitrogen excited species in the gas phase also points to a similar evolution towards a steady state level. The existence of transient regimes should not be disregarded when plasma jets are used for industrial and life science applications, where the exposure duration of biological targets, liquids, and solid state materials is usually of the order of a few minutes.