Direct Sensing of Superoxide and Its Relatives Reactive Oxygen and Nitrogen Species in Phosphate Buffers during Cold Atmospheric Plasmas Exposures.

This study aims at sensing in situ reactive oxygen and nitrogen species (RONS) and specifically superoxide anion (O2•-) in aqueous buffer solutions exposed to cold atmospheric plasmas (CAPs). CAPs were generated by ionizing He gas shielded with variable N2/O2 mixtures. Thanks to ultramicroelectrodes protected against the high electric fields transported by the ionization waves of CAPs, the production of superoxide and several RONS was electrochemically directly detected in liquids during their plasma exposure. Complementarily, optical emissive spectroscopy (OES) was used to study the plasma phase composition and its correlation with the chemistry in the exposed liquid. The specific production of O2•-, a biologically reactive redox species, was analyzed by cyclic voltammetry (CV), in both alkaline (pH 11), where the species is fairly stable, and physiological (pH 7.4) conditions, where it is unstable. To understand its generation with respect to the plasma chemistry, we varied the shielding gas composition of CAPs to directly impact on the RONS composition at the plasma-liquid interface. We observed that the production and accumulation of RONS in liquids, including O2•-, depends on the plasma composition, with N2-based shieldings providing the highest superoxide concentrations (few 10s of micromolar at most) and of its derivatives (hundreds of micromolar). In situ spectroscopic and electrochemical analyses provide a high resolution kinetic and quantitative understanding of the interactions between CAPs and physiological solutions for biomedical applications.

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

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.