Chemical and antibacterial effects of plasma activated water: correlation with gaseous and aqueous reactive oxygen and nitrogen species, plasma sources and air flow conditions

Abstract

When cold atmospheric plasma comes into contact with water and biological media, antimicrobial or antitumor effects are induced, representing great potential for applications in biomedicine and agriculture. The need to control and tune the chemical composition and biomedical effects of plasma activated water/media (PAW/PAM) is emerging. By comparing two nonthermal air plasma sources, streamer corona and transient spark, interacting with water in open and closed reactors, and by enhancing the plasma-liquid interaction by water electrospray through these discharges, we demonstrate that the plasma gaseous products strongly depend on the discharge regime, its deposited power and gas flow conditions. The streamer corona strongly leads to the formation of ozone and hydrogen peroxide, while the more energetic transient spark leads to nitrogen oxides and hydrogen peroxide. The gaseous products then determine the chemical properties of the PAW and the dominant aqueous reactive oxygen and nitrogen species (RONS). The production of hydrogen peroxide depends on water evaporation and hydroxyl radical formation, which is determined by the discharge power. A transient spark produces higher concentrations of gaseous and aqueous RONS and induces stronger antibacterial effects than a streamer corona; however, the RONS production rates per joule of deposited energy are comparable for both studied discharge regimes. The net production rate per joule of gaseous nitrogen oxides strongly correlates with that of aqueous nitrites and nitrates. The antibacterial effects of the PAW tested on Escherichia coli bacteria are determined by the aqueous RONS: in the lower power streamer corona, this is ascertained mainly by the dissolved ozone and hydrogen peroxide, and in the higher power transient spark, by the combination of hydrogen peroxide, nitrite and acidic pH, while in the transient spark in the closed reactor it is determined by the acidified nitrites present.

Direct Treatment of Liquids Using Low-Current Arc in Ambient Air for Biomedical Applications

“…It was found that the number of surviving E. coli was about 2 × 10 3 mL −1 after direct plasma treatment for 10 s and decreased to the colony counting method detection limit of 10 mL 1 after 30 s, showing a 6-log reduction in the concentration of bacteria. As shown in Figure 8, the bactericidal effect of treatment with AALCA was significantly higher than the bactericidal effect of treatment with NEAPRS and APPJ, corona, or DBD discharges reported elsewhere [9,43,[49][50][51][52][53][54][55][56]. It was confirmed by thermographic observation that the suspension was heated by irradiation to temperatures up to 38 • C, which is below the temperature harmful for E. coli reported elsewhere, suggesting that heating of the sample was not involved in the sterilization process [57].…”

Mode transition and plasma characteristics of nanosecond pulse gas–liquid discharge: Effect of grounding configuration

“…In the nitrogen discharge, the electron‐impact dissociation of N 2 will produce ground state N ( 2 D), N ( 2 P), and N ( 4 S), and then produce the excited state N (3 p ) via the electron‐impact excitation processes . The related reactions are shown as R1–R3 in Table .…”

“…The related reactions are shown as R1–R3 in Table . Ground state H atoms are generated through the electron dissociation of H 2 O, and excited to H ( n = 3) by electron excitation processes (see R4 and R5) . The quenching processes of metastable N 2 (A) or N atoms by H 2 O are other pathways to generate H atom (see R6 and R7) .…”

Removal of Microcystis aeruginosa through the Combined Effect of Plasma Discharge and Hydrodynamic Cavitation

“…The emission spectra, showing atomic oxygen, atomic hydrogen and excited nitrogen molecules/ions in the discharge, clearly indicate that water vapour molecules were dissociated to OH radicals. The presence of excited nitrogen molecules and atomic oxygen also suggests the presence of nitrogen oxide species [23], commonly observed in discharge spectra of discharges used to produce RONS in water [24,25]. While other spectroscopic methods (e.g., Fourier transform infrared absorption, laser absorption, electron paramagnetic resonance), along with fluorescence/colorimetric measurements [22,26,27], may be better placed to confirm and quantify RONS, our own spectroscopic evaluation clearly showed production of RONS by HC + plasma.…”