Mistifying the Fourth State of Matter: Characterizing a Plasma Jet and Water Interface for Applications in Medical Treatment

Abstract

Plasma is referred to as the fourth and most energetic state of matter; it is similar to a gas of positive ions and electrons, but it can carry an electric current, its constituents behave as a collect unit, and it is macroscopically neutrally charged. This interesting property has allowed people to harness the power of plasma for many different applications, including digital displays, lighting, dry etching in semiconductor chip technology, and most recently medical treatment. Plasma can be generated at various temperatures and pressures, but atmospheric pressure low-temperature plasma is particularly interesting when it comes to medical treatment, since it can safely interact with biological cells. Through the rise of atmospheric pressure plasma, medical applications have increased in the past decade. Recent studies have shown that medical treatment using low temperature plasma can heal chronic wounds and even kill cancer cells. One study was able to kill breast cancer cells through apoptosis with an atmospheric pressure plasma jet created by a pulsed electric field. In order to harness this complex power of plasma, it is important to first understand it. Plasma medicine is the cross functional field of study that brings biologists and engineers together to study these phenomena. While it is the biologist’s task to discover the mechanisms with which the plasma interacts with biological cells, it is the engineer’s job to discover what chemical quantities exist in plasma, and develop a means for controlling the reactive species composition. This project aims to understand the chemical composition of a low temperature plasma jet and water interface.

Although most plasmas are well studied, low temperature plasma, especially when it is in contact with water, is still in need of basic research. Recently, the plasma-liquid interface has been identified as one of the most relevant regions of interest. To study this type of plasma-liquid interaction in the necessary environment, an experimental set-up was made to study plasma and water interactions with a design emphasis on ease-of-use. Most importantly, a direct optical access to the plasma-liquid interface was included. This set-up was used to measure chemical species concentrations using spectroscopic methods. Reactive oxygen species concentrations, specifically ozone concentration, is of particular interest because of its relevance in recent biological studies showing it's role in killing cancer cells. Ozone is one of the most abundant reactive species in plasma and controlling its generation will allow us to understand the processes that lead to its generation, as well as control less abundant species. A chemical kinetics theoretical model was utilized to understand how these chemical species concentrations change over time in an oxygen plasma created by a pulsed electric field. These results will lead to the ability to control the reactive species concentrations generated by the plasma, and therefore create a tool that allows for fundamental research in the field of plasma medicine. Once this precise composition is determined, it can be used as a trigger for in-vitro biological studies that lead to a response that can be understood by data analysis tools. This data can lead to the insights required for developing novel therapies, such as cancer treatment.