Reactive Oxygen Species Generated by Cold Atmospheric Plasmas in Aqueous Solution: Successful Electrochemical Monitoring in Situ under a High Voltage System

Abstract

Many investigations are dedicated to the detection and quantification of reactive oxygen and nitrogen species (RONS), particularly when generated in liquids exposed to cold atmospheric plasmas (CAPs). CAPs are partially ionized gases that can be obtained by applying a high electric field to a gas. A challenge is to get better insights on the plasma–liquid interactions in order to understand the induced effects on different targets (liquid, cells, tissues, etc.). As RONS are biochemically reactive, the difficulty lies in finding efficient methods to get both dynamic and quantitative data. Herein, we developed an innovative setup aimed at performing an in situ electrochemical monitoring of redox species generated by CAPs in a physiological buffer (PBS, pH 7.4). The challenge was to apply millivolt-potential variations and measure nanoampere Faradaic currents in the presence of ionization waves generated by micropulsed electric fields of some 10 kV·cm–1 amplitude and ampere-transient currents. This was fulfilled by using dedicated working ultramicroelectrodes (Pt-black UMEs) and protecting them, as well as the reference and counter electrodes, within insulated-earthed containers. In this condition, we succeeded in performing both cyclic voltammetry and chronoamperometry in situ, with a resolution equivalent to working in a static solution (subnanoampere currents). Thus, we monitored the accumulation over time of species (H2O2, NO2 –) generated by CAPs in PBS and observed the mean dynamic of RONS chemistry during and after plasma exposition, particularly through the detection of a short-living species.

Human Trial for the Effect of Plasma-Activated Water Spray on Vaginal Cleaning in Patients with Bacterial Vaginosis

“…Generally, plasma irradiation at atmospheric pressure induces various ionized gases and free radicals that originate primarily from oxygen and nitrogen gases in the air and water [18][19][20]. In particular, oxygen-derived free radicals such as superoxide anions and hydroxyl ions are responsible for the antibacterial activity [21][22][23]. Additionally, many previous studies also support that underwater plasma exposure to chlorinated tap water can increase free residual chlorine molecules such as hypochlorous acid and hypochlorite ions, eliminating harmful microorganisms [24,25].…”

Dynamics of Singlet Oxygen-Triggered, RONS-Based Apoptosis Induction after Treatment of Tumor Cells with Cold Atmospheric Plasma or Plasma-Activated Medium

“…The gaseous and liquid phase of CAP contains electrons, photons, superoxide anions (O 2 ●− ), hydroperoxyl radicals (HO 2 ● ), hydrogen peroxide (H 2 O 2 ), hydroxyl radicals ( ● OH), atomic oxygen (O), singlet oxygen ( 1 O 2 ), ozone (O 3 ), nitric oxide ( ● NO), nitrogen dioxide ( ● NO 2 ), peroxynitrite (ONOO − ), nitrite (NO 2 − ), nitrate (NO 3 − ), dichloride radicals (Cl 2 ●− ) and hypochloride anions (OCl − ) 3,16,37,38 . Due to the high reactivity and short live time of most CAP-derived species, PAM (as well as other plasma-activated liquids) essentially contains only H 2 O 2 , NO 2 − and NO 3 − 33,39–41 . It is intriguing that a liquid with a RONS composition of such an apparently low complexity can trigger impressive antitumor effects in many tumor systems in vitro and in vivo , as shown by many groups 5,14,30,33–36,40,42–51 , and reviewed by Yan et al .…”

Electrodes and electrocatalysts for electrochemical hydrogen peroxide sensors: a review of design strategies

“…4c shows a probe with microelectrodes sealed in an insulated container, used to monitor H 2 O 2 related ROS generated in cold atmospheric plasma under ultrahigh voltages. 82 It is desirable to evaluate the defense potential of biofilms against electrochemically produced H 2 O 2 in bioelectrochemical systems. However, it is impossible to measure H 2 O 2 concentrations under the interference of a strong electric field using common electrodes.…”