Comparison of different Plasma Activated Water produced by different plasma devices by optical and analytical techniques

The work was carried out at the Laboratory of Optical Diagnostics under the leadership of Dr. Milan Šimek. Two reactors designed at the ISTP-Bari laboratory were used to produce Plasma Activad Water (PAW): -Surface Dielectric Barrier Discharge (SDBD) plasma reactor: smaller volume, higher concentration of Reactive Oxygen and Nitrogen Species (RONS) in the PAW; -Volume DBD (VDBD) plasma reactor: larger volume, lower concentration of RONS in the PAW. At the end of this STSM we were able to achieve a better understanding on the comprehensive chemical composition of the PAW produced in the VDBD reactor designed in Bari, while more work is still needed to characterize the PAW produced in the SDBD reactor. The species detected by ionic chromatography, using an analysis protocol based on an already existing one designed by Dr. P. Lukes, where mainly H2O2, NO2- and NO3-. Based on the concentration of these species and on the measured pH values, it was possible to infer from kinetic calculations that the concentration of more unstable and harder to detect species like peroxynitrite is too low (or the species are too short-lived in the PAWs) to really play a definite role in the interaction mechanism between the liquid and the fungi it was tested on. Ionic chromatography was also used to check the consistency of different quantification among one another. From the gathered results, we could conclude that the chemical characterization of PAWs performed by standard colorimetric tests, carried out with a portable photometer and commercially available reactants and protocols, is consistent with the one obtained by ionic chromatography, within a 10% interval that can be attributed to experimental error. The chemical analyses were combined with biological experiments aimed at evaluating the decontaminating properties of the produced PAW against fungi. The eventual conidial inhibition reached at different levels for different treatment conditions allowed for the fine-tuning of the discharge characteristics towards its antimicrobial effects. Transcriptomic studies on the treated samples are planned in order to better understand the mechanisms of interaction between reactive species and cells. Gas-phase species produced by the plasma was assessed as planned through spectroscopic analyses, using optical emission, FTIR and UV-adsorption. In particular, FTIR ex and in situ analyses were pivotal in clarifying the interaction of plasma-created species with the liquid medium (water) for different discharge conditions. Finally, taking all the results into account, it was possible to evaluate which species are the most significant for the decontaminating effect of PAW obtained using the VDBD reactor (acidic nitrates), while more analyses are still needed to draw similar conclusions about the SDBD-produced PAW. Still, this collaboration proved successful in the optimization of the discharge parameters that are utilized in PAW production.