Chemistry and biochemistry of cold physical plasma derived reactive species in liquids

Reactive oxygen and nitrogen species deposited by cold physical plasma are proposed as predominant effectors in the interaction between discharge and biomedical application. Most reactive species found in plasma sources are known in biology for inter- and intracellular communication (redox signaling) and mammalian cells are equipped to interpret the plasma derived redox signal. As such, considerable effort has been put into the investigation of potential clinical applications and the underlying mechanism, with a special emphasis on conditions orchestrated significantly via redox signaling. Among these, immune system control in wound healing and cancer control stands out with promising in vitro and in vivo effects. From the fundamental point of view, further insight in the interaction of the plasma-derived species with biological systems is desired to (a) optimize treatment conditions, (b) identify new fields of application, (c) to improve plasma source design, and (d) to identify the trajectories of reactive species. Knowledge on the biochemical reactivity of non-thermal plasmas is compiled and discussed. While there is considerable knowledge on proteins, lipids and carbohydrates have not received the attention deserved. Nucleic acids have been profoundly investigated yet focusing on molecule functionality rather than chemistry. The data collected underline the efforts taken to understand the fundamentals of plasma medicine but also indicate 'no man's lands' waiting to be discovered.