## 3 Applications of Cold Atmospheric Pressure Plasma
### Medicine
used pseudoviruses with the SARS-CoV-2 S protein as a model (for biosafety limitations), and showed that plasma-activated water effectively inhibited pseudovirus infection through S protein inactivation [70]. Decontamination procedures of pathogenic viruses in different media and on various surfaces could help to limit virus spread [43]. [PERSON] et al. studied SARS-CoV-2 inactivation using APPJ with argon and helium feed gas on various surfaces including plastic, metal and leather (the discharge voltages for argon and helium were 16.8 kV and 16.6 kV at 12.9 kHz and 12.7 kHz frequency, flow rate 6.4 L/min and 16.5 L/min). The roughness, material composition and absorptivity were aspects that influenced surface inactivation of SARS-CoV-2. The argon plasma treatment inactivated all viruses in less than 180 s. Helium plasma did not disinfect all viruses on surfaces even at 300 s because of the much lower RONS concentrations compared to argon plasma for the same operating conditions. The results confirmed the important role played by RONS concentration in virus inactivation. Comprehension of how SARS-CoV-2 interacts with CAPP is essential for future plasma utilization. [71]. The spread of SARS-CoV-2 is mostly via the transmission of respiratory droplets in poorly ventilated closed spaces [72]. It is important to try to improve the indoor air quality, e.g., by reducing the airborne time of SARS-CoV-2 aerosol microdroplets. [PERSON] et al. used a lab-scale dielectric barrier discharge plasma source to inactivate aerosols containing purified SARS-CoV-2 RNA suspension flowing through the device. Results show that CAP can degrade viral RNA in a short residence time (<0.2 s) [73]. The virus contains nucleic acids encased in a capsid protein coat. Reactive oxygen and nitrogen species have been shown to be responsible for virus inactivation through effects on capsid proteins, which preceded the degradation of nucleic acids. RONS can disrupt virus integrity by etching away the protein protective layer, and then act directly on nucleic acids, damaging the genetic material used for virus genome translation and replication. CAPP treatment can result in loss of viral infectivity [24; 74]. Application of cold plasma is expected to decontaminate face masks or shields from SARS-CoV-2 surrogates without affecting their filtration and fitting performance [24; 75]. Furthermore, CAPP can be used as an alternative to alcohol-based hand disinfection [76]. Hands are one of the most common transmission routes for many infections because people frequently touch their facial mucous membranes--the eyes, nose and mouth, which are the main portal of entry for germs [24, 43]. Sterilization using CAPP is a fast and efficient method, which is essential in healthcare institutions. However, some undesirable effects have to be solved (e.g., ozone is a toxic byproduct) by optimization of the geometry of the hand dispensary system [76]. Based on early and incomplete results, CAPP has potential in inactivating different types of viruses in the near future, but confirmation will be required, because studies are in their infancy at present. Scientists anticipate that CAPP will be an effective and environmentally friendly tool to replace, complement, or upgrade existing sterilization methods, mitigating the economic and public health burdens of the pandemic [43]. [PERSON] et al. analyzed in full theoretical detail the influence of oxidation on the SARS-CoV-2 CTD protein structure and the SARS-CoV2-CTD/hACE complex. Via molecular dynamics, the basic statistical characteristics, relative binding free energy of the oxidized complex and the effect of CAPP-induced oxidation on the stability/flexibility have been determined. It was shown that the protein structures are sensitive to radical oxygen and the binding free energy (without entropic term) is lowered as a consequence of the plasma oxidation. However, the inactivation mechanism of SARS-CoV by CAPP is still an open problem, the application of cold plasma seems to be a very prospective method in this field [77].