# Multimodal Comparison of Cold Atmospheric Plasma Sources for Disinfection
## 5 Conclusions  
Plasma medicine is a constantly growing field, already reaching clinical practice with some of its most studied technologies. However, the chain of components and processes involved in the interaction between plasma, atmosphere, liquids, and cells remains obscure in many aspects. The presence of numerous sources in various laboratories used for widely disparate applications represents an obstacle in defining a common standard which suits the research groups involved. An extensive campaign of source characterisation, following strict protocols and unified operating conditions, is fundamental to further understand the mechanisms involved, and therefore to design optimised sources that maximize the desired effects while preventing collateral damages.  
This work presents a proof of concept for such a campaign. Multiple sources with multiple diagnostics were tested on a fixed common setup. The protocol was defined in detail, allowing for its reproduction in different laboratories. The obtained measurements range from physical to chemical and biological analyses.  
The three different sources, in a total of five configurations, span six orders of magnitude in terms of biological effects. Connecting the physiochemical characterisation of the treated samples with the response of treated cells still remains a challenge. Indirect treatments, performed in the same setup as direct ones, led to excluding short-timescale phenomena from playing a key role in the considered treatments, confirming the fundamental importance of long-lived RONS. The chemical characterisation of the treated samples reported different equilibriums between oxygen and nitrogen species. These results well reflect the differences in nitrogen rotational and vibrational temperatures measured via emission spectroscopy, which can therefore be used as a real-time probe of the ongoing treatment. The analysed sources do not induce any significant change in pH, and in particular the samples treated with the micropulsed helium source reach more than 6 logAbat in a neutral solution, highlighting that acidification is not fundamental as reported in other setups [52]. Finally, the results from the chemical characterisation prove that the biological effects cannot be connected to an individual species: the samples with highest concentration of specific RONS does not coincide with the samples with the highest bacterial abatement, suggesting the presence of an optimal mix of nitrates, nitrites, peroxides (and eventually other species not measured here) for an efficient bactericidal effect. These comparisons between different sources and diagnostics have been possible thanks to the common setup in which all diagnostics are gathered together and the sources are adapted, confirming the need to define a complete and common protocol to obtain meaningful data.  
Further steps will involve enriching the diagnostic methods, aiming to add more detail to the source characterisation while maintaining the consistency of the setup and protocol, and broadening the range of available sources, gathering more evidence toward a full understanding of the entire process.  
Conceptualization, L.Z., C.R., I.F. and E.M.; Methodology, L.Z., R.A., I.F. and E.M.; Investigation, L.Z., R.A. and B.M.; Resources, R.C., L.C., G.D.M., M.Z., I.F. and E.M.; Data curation, L.Z.; Writing--original draft, L.Z.; Writing--review and editing, L.Z., R.A., B.M., I.F. and E.M.; Visualization, L.Z.; Supervision, I.F. and E.M.; Funding acquisition, C.R. and I.F. All authors have read and agreed to the published version of the manuscript.  
The work presented in this article was made possible by a Short Term Scientific Mission funded by the COST Action PlasTHER \"Therapeutical applications of cold plasmas\" (CA20114), supported by COST (European Cooperation in Science and Technology).  
Dataset available on request from the authors.  
The authors declare no conflicts of interest.