## Results and Discussion
### Characteristics of the Plasma-Activated Water Produced by the Soft Plasma Jet
reported that the concentrations of \(H_{2}O_{2}\) and nitrate in PAW treated for 5 min by DBD plasma with plane-parallel electrodes were measured to be 114.04 uM (indirect)/403.84 uM (direct) and 150.0 uM (indirect)/1.14 mM (direct), respectively [23]. The PAW was prepared by treating DI water with a DBD plasma device that consisted of two circular aluminum plate electrodes (158 mm diameter) over polypropylene dielectric layers (2 mm thickness). In this work, the PAW was prepared by activating DI water with an electric shock-free, nonthermal atmospheric pressure air plasma jet. The level of RONS in the PAW generated by the soft plasma jet are comparable to those generated by the DBD plasma. To further investigate the plasma-induced reactive nitrogen species, the optical absorption spectra of the PAW were measured. As shown in Figure 2a,b, the nitrite and nitrate reference solutions exhibited absorption peaks at 209.2 and 200.8 nm, respectively. The PAW exhibited an absorption peak at 205.5 nm, indicating that both nitrite and nitrate ions coexist in the PAW. Figure 3 exhibits the absorption spectra of the PAW in the wavelength region of 300-420 nm. For all the plasma activation times of 1, 3, 6, and 10 min, the absorption spectra of the PAW in Figure 3a exhibit four absorption peaks at 346.8, 358.1, 371.0, and 386.0 nm, respectively, attributable to the \(n-\pi^{*}\) electronic transition of aqueous \(NO_{2}^{-}\) and \(HNO_{2}\). Meanwhile, the nitrite reference solutions exhibit a single absorption peak at 347 nm, as shown in Figure 3b. This result indicates that the PAW contains \(HNO_{2}\) as well as \(NO_{2}^{-}\). On comparing the measured absorption spectrum of the PAW with the molar absorption coefficients of \(HNO_{2}\), \(NO_{2}^{-}\), and \(NO_{3}^{-}\), which are described in the literature [44; 45; 46; 47], the concentrations of \(HNO_{2}\), \(NO_{2}^{-}\) and \(NO_{3}^{-}\) in the PAW were estimated to be 0.59 mM, 0.72 mM, and 1.04 mM, respectively. When \(NO_{x}\) was approximated as the sum of \(HNO_{2}\), \(NO_{2}^{-}\), and \(NO_{3}^{-}\), the concentration of \(NO_{x}\) measured by optical absorption spectra of the PAW in 300-420 nm was 2.3 mM. This concentration is comparable to that measured by a Nitric Oxide Assay Kit (DIOX-100). Under acidic conditions, the formation of conjugate acids (\(HO_{2}\), \(HNO_{2}\), and \(HNO_{3}\)) corresponding to \(O_{2}^{-}\), \(NO_{2}^{-}\), and \(NO_{3}^{-}\) could play an important role in the inactivation of fungal spores. These results demonstrate that the PAW produced by our soft plasma jet device contains RONS that react readily with cellular components such as lipids, proteins, carbohydrates, and nucleic acids and may result in significant damage to cell structures, cumulating in a condition known as oxidative stress [42; 48]. Viability of the A. brasiliensis Spores Treated with Plasma-Activated Water and Chemically Induced RONS Solutions  
Both the PAW and the direct plasma treatments against _A. brasiliensis_ spores revealed that they have a remarkable effect on the viability of the spores, as seen in Figure 4a. The PAW treatment clearly reduced spore viability. A reduction of the spore viability tended to increase with the treatments of PAW that had longer plasma activation times. After being treated for 30 min in the PAW with a plasma activation time of 3 min, the spore viability dropped sharply to 15%, indicating that the PAW treatment significantly inactivated 85% of the tested spores. The spore viability also quickly dropped to 9% when the spores were treated directly with the soft plasma jet for 3 min. This result indicates that the viability of the PAW-treated spores is almost comparable to that of the spores treated directly with plasma. These results demonstrated that the PAW produced by the soft plasma jet can be applied in fungal spore inactivation.