# Biological Decontamination by Microplasma
## 4 Discussions  
The microplasma discharge in air generates reactive oxygen species (ROS) such as O, O\({}_{2}\)(a\({}^{1}\Delta_{g}\)) and O\({}_{3}\), and reactive nitrogen species (RNS) such as NO, NO\({}_{2}\), and ONOO\({}^{-}\)[16; 40; 41; 42]. The discharge using room-temperature air benefits from the presence of water vapor; thus, H\({}_{2}\)O\({}_{2}\), OH, HNO\({}_{3}\), and HNO\({}_{2}\) are also generated. The mechanisms responsible for the generation of ROS and RNS by microplasma are initiated by the electron impact dissociation of O\({}_{2}\), N\({}_{2}\), and H\({}_{2}\)O (humidity in room \begin{table}
\begin{tabular}{l l l l l} \hline \hline  & \multicolumn{4}{c}{**CFU**} \\ \cline{2-5}  & \multicolumn{2}{c}{\(-\)**1.5 kV**} & \multicolumn{2}{c}{\(-\)**1.7 kV**} \\ \hline  & **Treated** & **Control** & **Treated** & **Control** \\ \hline _E. coli_ & 279 \(\pm\) 77.7 & 348 \(\pm\) 44.6 & 222.5 \(\pm\) 13.4 & 348 \(\pm\) 44.6 \\ _P. aeruginosa_ & N.A. & N.A. & N.A. & N.A. \\ _S. aureus_ & 35.5 \(\pm\) 6.3 & 205 \(\pm\) 103.9 & 287 \(\pm\)69.3 & 205 \(\pm\) 103.9 \\ \hline mean \(\pm\) s.d.; N.A.—not applicable. & & & & \\ \end{tabular}
\end{table} 
Table 1: Colony-forming units developed after 24 h after microplasma treatment at \(-\)1.5 and \(-\)1.7 kV. Figure 6: Inhibition-zone measurement for bacterial strains treated with microplasma at \(-\)1.7 kV. temperature air). Some ROS and RNS are generated at this stage, as well as the reactive products that are further necessary to form other ROS and RNS [43]:  
\[\mathrm{e}+\mathrm{O}_{2}\rightarrow\mathrm{O}+\mathrm{O}+\mathrm{e} \tag{5}\]  
\[\mathrm{e}+\mathrm{N}_{2}\rightarrow\mathrm{N}+\mathrm{N}+\mathrm{e} \tag{6}\]  
\[\mathrm{e}+\mathrm{H}_{2}\mathrm{O}\rightarrow\mathrm{OH}+\mathrm{H}+\mathrm{e} \tag{7}\]  
\[\mathrm{e}+\mathrm{H}_{2}\mathrm{O}\rightarrow\mathrm{H}+\mathrm{H}+\mathrm{O}+ \mathrm{e} \tag{8}\]  
\[\mathrm{e}+\mathrm{H}_{2}\mathrm{O}\rightarrow\mathrm{H}_{2}+\mathrm{O}+ \mathrm{e}. \tag{9}\]  
The electrons are losing energy mainly through inelastic collisions that are responsible for producing excited states of O\({}_{2}\), N\({}_{2}\), and H\({}_{2}\)O. These electronically, rotationally, or vibrationally excited states are O\({}_{2}\)(\(r\)), O\({}_{2}\)(\(p\)), O\({}_{2}^{\ast}\), O\({}_{2}\)(\({}^{1}\)S), N\({}_{2}\)(\(r\)), N\({}_{2}\)(\(v\)), N\({}_{2}^{\ast}\), or H\({}_{2}\)O(\(v\)). The formation of NO consists of the electronically excited states of N\({}_{2}\) (N\({}_{2}^{\ast}\)) which are quenched dissociatively by O\({}_{2}\) to produce O atoms, and furthermore participate in reactions with O. The three-body reaction of O\({}_{2}\) and O produces ozone (O\({}_{3}\)) [44]:  
\[\mathrm{O}+\mathrm{O}_{2}+\mathrm{M}\rightarrow\mathrm{O}_{3}+\mathrm{M} \tag{10}\]  
where M is a third collision partner: O, O\({}_{2}\) or O\({}_{3}\). The direct three-body recombination is the mechanism for production of O\({}_{2}\)(a\({}^{1}\Delta_{g}\)) [45]:  
\[\mathrm{O}+\mathrm{O}+\mathrm{M}\rightarrow\mathrm{O}_{2}(\mathrm{a}^{1} \Delta_{g})+\mathrm{M}. \tag{11}\]  
The third body M can be in room-temperature air, primarily as O\({}_{2}\)/N\({}_{2}\), but can also be a third oxygen atom. ROS, RON, and also UV light affect the cell envelope and internal components of bacteria. Due to these active species, the cellular envelope collapses and the intracellular components (DNA) are damaged [18,46]. [PERSON] et al. [9] pointed out the differences between the inactivation mechanism of _E. coli and S. aureus_. For _E. coli_, a Gram-negative bacteria, the main reason for the inactivation process occurs due to the action of ROS and RNS on the cell envelope; thus, the cell envelope of _E. coli_ is affected and leads to cellular swelling, rupture, and cytoplasmic leakage. Furthermore, a denaturation of biomacromolecules occurs because ROS and RNS enter excessively into the intracellular milieu. For _S. aureus_, a Gram-positive bacteria, the deactivation mechanism consists of the accumulation in excess of ROS and RNS on internal structures. _S.