# Water Modification by Cold Plasma Jet with Respect to Physical and Chemical Properties
## 3 Results and Discussion
### Liquid Treatment--ROS Detection  
Following the above observations on the plasma induced modifications of the water, the next step is their interrogation in terms of ROS formation. Thus, here follows the identification and quantification of the ROS components \({}^{\bullet}\)OH, H\({}_{2}\)O\({}_{2}\) and O\({}_{2}^{\bullet-}\) generated by the plasma jet in both DDW and PBS. Tables 2 and 3 summarize the results for the treatment time of 30 min. The radical \({}^{\bullet}\)OH is identified by its specific probe TPA against the control conditions (i) of non-exposure to the plasma and (ii) exposure in the presence of its specific scavenger DMSO. As \({}^{\bullet}\)OH is being produced in DDW or PBS due to the plasma exposure, in the presence of excess TPA, the concentration of 2-OH-TPA (thus, of \({}^{\bullet}\)OH) increases linearly over time, reaching about 550 nM in DDW at 30 min. H\({}_{2}\)O\({}_{2}\) identification and quantification employ an established specific method [36], using as a control condition the non-exposure to the plasma. In addition, the use of the \({}^{\bullet}\)OH-specific scavenger DMSO [47; 48] as an additional control condition ensures that H\({}_{2}\)O\({}_{2}\) produced in the plasma-treated liquid is not produced by the recombination of 2 moles \({}^{\bullet}\)OH. This control translates to a concentration of about 350 uM of H\({}_{2}\)O\({}_{2}\) in DDW after 30 min of plasma exposure. A similar approach to that of the \({}^{\bullet}\)OH is followed for the detection of O\({}_{2}^{\bullet-}\) by its specific probe HE with two independent innovative methodologies [33; 37]. The non-exposure control condition is also used, and the produced concentration is around 850 nM in DDW after 30 min of plasma exposure. The corresponding concentrations in PBS are about 450 nM, 250 uM, and 80 nM (\({}^{\bullet}\)OH, H\({}_{2}\)O\({}_{2}\), and O\({}_{2}^{\bullet-}\), respectively). However, the recorded \({}^{\bullet}\)OH and O\({}_{2}^{\bullet-}\) levels are considered minimum. The reasons being: (i) these radicals are only those being trapped by their respective probes TPA and HE during 30-min plasma exposure; (ii) their quantification is made by the respective 2-OH-TPA and 2-OH-E\({}^{+}\) (i.e., products of the reaction of \({}^{\bullet}\)OH and O\({}_{2}^{\bullet-}\) with their respective probes TPA and HE) that survived plasma oxidation; and (iii) only part of HE forms 2-OH-E\({}^{+}\) with O\({}_{2}^{\bullet-}\) while the other part is converted to non-specific oxidation products by 1 or 2 electron-oxidation [49; 50; 51]. Regarding H\({}_{2}\)O\({}_{2}\), its concentration is similar in both the DDW and the PBS (about 25% lower in PBS). Another factor adding to the difficulty in obtaining absolute production values for \({}^{\bullet}\)OH, O\({}_{2}^{\bullet-}\) and H\({}_{2}\)O\({}_{2}\) is their participation in numerous side reactions involving both their generation and destruction [12; 14; 15; 52; 53; 54; 55; 56; 57; 58]. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \({}^{\bullet}\)**OH (2-OH-TPA) (nM)** & **H\({}_{2}\)O\({}_{2}\) (uM)** & \(\Delta\)**pH** \\ \hline Plasma-exposed: TPA in DDW & 565 (565) \(\pm\) 27 & 359 \(\pm\) 17 & 2 \(\pm\) 0.02 \\ Plasma-exposed: TPA + DMSO & 0 (0) & 336 \(\pm\) 15 & 2 \(\pm\) 0.01 \\ (\({}^{\bullet}\)OH scavenger) in DDW & 0 (0) & 0 (0) & 0 \(\pm\) 0.02 \\ Plasma-non-exposed: TPA in DDW & 481 (481) \(\pm\) 23 & 255 \(\pm\) 11 & 0 \(\pm\) 0.02 \\ Plasma-exposed: TPA + DMSO & 0 (0) & 263 \(\pm\) 13 & 0 \(\pm\) 0.02 \\ (\({}^{\bullet}\)OH scavenger) in PBS & 0 (0) & 0 (0) & 0 \(\pm\) 0.01 \\ Plasma-non-exposed: TPA in PBS & 0 (0) & 0 (0) & 0 \(\pm\) 0.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Plasma generated \({}^{\bullet}\)OH and H\({}_{2}\)O\({}_{2}\) in DDW and PBS; values are averages from 5 repeats, with standard deviation around 5%.