Influence of NaCl concentration on reactive species formation in plasma-activated saline solutions using coaxial DBD

Abstract Plasma-Activated Saline Solutions (PAS), derived from Plasma-Activated Water (PAW), are increasingly recognized for their versatile applications in infection control, wound healing, and sterilization. These solutions are produced by exposing liquids to cold plasma, generating a rich mixture of reactive oxygen and nitrogen species (RONS) and reactive chlorine species (RCS). This study investigates the production of PAS using a coaxial dielectric barrier discharge (DBD) operating with compressed air and evaluates the impact of varying sodium chloride (NaCl) concentrations (0.9%, 1.8%, 3.6%, and 7.2%) on the generation of RONS and RCS. Deionized water (DI water) was also activated as a baseline comparison. Physicochemical properties, including pH, oxidation–reduction potential (ORP), conductivity, and total dissolved solids (TDS), were measured before and after plasma activation. Real-time UV–Vis and Raman spectroscopy were employed to monitor the formation and stability of reactive species. To complement the UV–Vis data, additional analytical methods, such as colorimetric test strips and estimations based on pH and equilibrium constants, were employed. The analyses revealed that NaCl concentration significantly influences the composition and behavior of PAS, with lower concentrations favoring the generation of RONS such as nitrites ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">NO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo>−</mml:mo> </mml:msup> </mml:math> ) and nitrates ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">NO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> <mml:mo>−</mml:mo> </mml:msup> </mml:math> ), while higher concentrations modulate the production of RCS like hypochlorous acid (HClO). The results demonstrated a pronounced decrease in pH and an increase in ORP, indicating enhanced oxidative and antimicrobial potential. Spectroscopic analyses revealed distinct patterns of RONS formation, including <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">NO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> <mml:mo>−</mml:mo> </mml:msup> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">NO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo>−</mml:mo> </mml:msup> </mml:math> , H 2 O 2 , and HClO, with notable interactions between RCS and RONS at higher NaCl concentrations. These findings underscore the dynamic interplay between ionic strength, reactive species production, and solution stability, providing critical insights into optimizing PAS for biomedical applications. The study highlights PAS’s potential as eco-friendly, residue-free alternatives for disinfection and wound care, offering tailored properties based on NaCl concentration to meet specific therapeutic needs.