## 3 Applications of Cold Atmospheric Pressure Plasma  
### Medicine  
In the past 20 years, cold plasma treatment has been extended to medicine, mainly as a tool for the inactivation of pathogens (bacteria, fungi, viruses, biofilms) on medical or laboratory equipment (e.g., surgical instruments, pharmaceutical devices, implants, dialysis tubes, glassware, plastic tubes, pipette tips, beds, floors, etc.) [42; 43; 44]. Conventional methods for disinfection (inactivation of pathogenic organisms) and sterilization (elimination of all viable microorganisms), such as steam and heat treatment, autoclaves, irradiation, wet chemical treatment (ethylene oxide, ozone, chlorine, hydrogen peroxide, sodium hypochlorite, alcohol or any carbohydrate solutions, superoxidized water, various kind of acids, etc.) and UV light exhibit several drawbacks [45]. They are often slow-acting, flammable or unstable at ambient conditions [46]. Moreover, they can cause irreversible damage to the modified material and irritate the skin and eyes of humans [47]. On the contrary, CAPP can be utilized for heat labile or chemically reactive materials (e.g., heat sensitive biomaterials, polymers, living tissues) to prevent secondary infections. Two basic types of CAPP systems are dominating in plasma medicine: indirect (e.g., plasma jet, pen, needle) and direct (e.g., dielectric barrier discharge device) plasma sources [26; 36; 48; 49]. In the direct exposure mode, the plasma is in contact with the biological target. Floating electrode DBD (FE-DBD) system allows safe usage of plasma in therapeutic applications. It consists of two electrodes, the first is a dielectric-protected powered electrode and the second electrode is a human or animal body (skin or organ) [41; 50]. Direct application of CAPP requires high standards of safety (e.g., homogeneous discharge with permitted values has to be created in order to provide nondestructive treatment). Indirect plasma sources do not use the human tissue as a counter electrode, the afterglow of plasma or plasma-activated liquid (it can be stored and shipped) is used [49; 51]. Typically, these devices are portable, and allow efficient treatment of large areas even with uneven surfaces. However, their homogeneity and stability need further improvement [47]. Plasma sources produce reactive species (with a lifetime ranging from nanoseconds to hours), which are known from redox biology and play a pivotal role in biological applications [52; 53; 54; 55; 56; 57]. Reactive oxygen-based species (ROS) include, e.g., superoxide (O\({}_{2}^{\bullet-}\)), hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)), hydroxyl radical (\({}^{\bullet}\)OH), singlet oxygen (\({}^{1}\)O\({}_{2}\)), ozone (O\({}_{3}\)), alkoxyl (RO\({}^{\bullet}\)) and peroxyl (RO\({}_{2}^{\bullet}\)). Nitrogen-based species include (RNS), e.g., nitric oxide (\({}^{\bullet}\)NO), nitrogen dioxide (\({}^{\bullet}\)NO\({}_{2}\)) and peroxynitrite (ONOO\({}^{-}\)). These reactive species (ROS/RNS=RONS) also play a crucial role in the pathogen inactivation mechanism (Figure 2), because they can modulate the environment of cells and affect their behavior [30; 48; 49; 58; 59]. RONS can cause cell wall erosion, cell membrane disruption (protein denaturation, virus leakage), functionality changes (oxidation of amino acids), damage to DNA and RNA and apoptosis [43; 57; 60]. However, it should be pointed out that the precise mechanism of microbial inactivation using CAPP treatment and the contribution of various components (UV, electrons, ion bombardment and reactive species) has not yet been fully understood [61]. Drug resistance and incurable bacterial infections are serious public health threats, as the world is heading towards a post-antibiotic era, mainly caused by the misuse and overuse of various medications [62]. It is an urgent need to develop new techniques to treat infectious diseases caused by multidrug-resistant germs.