Fluorescence measurements of peroxynitrite/peroxynitrous acid in cold air plasma treated aqueous solutions

• Published in: Physical chemistry chemical physics : PCCP 2019-04, Vol.21 (17), p.8883-8896
• Main Authors: Tarabová, Barbora, Lukeš, Petr, Hammer, Malte U, Jablonowski, Helena, von Woedtke, Thomas, Reuter, Stephan, Machala, Zdenko
• Format: Article
• Language: English
• Subjects: Acids; Air plasma; Aqueous solutions; Buffers; Diagnostic systems; Electric sparks; Fluorescence; Fluorescent dyes; Hydrogen peroxide; Nitrites; Nitrogen dioxide; Organic chemistry; Plasma; Reaction kinetics; Scavenging; Selectivity; Sensitivity
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c9cp00871c

Qualitative detection of peroxynitrite/peroxynitrous acid (ONOO − /ONOOH) as one of the key bactericidal agents produced in cold air plasma activated aqueous solutions is presented. We examined the use of the 2,7-dichlorodihydrofluorescein diacetate (H 2 DCFDA) fluorescent dye to detect ONOO − /ONOOH in plasma activated non-buffered water (PAW) or buffered solution (PAPB) generated by DC-driven self-pulsed transient spark discharge at atmospheric pressure in ambient air. The diagnostic selectivity of H 2 DCFDA to reactive oxygen and nitrogen species (RONS) typical of plasma activated aqueous solutions was examined by using various scavengers of RONS. This cross-reactivity study showed the highest sensitivity of the H 2 DCFDA dye to ONOO − /ONOOH. However, besides ONOO − /ONOOH, H 2 DCFDA also exhibited sensitivity to hypochlorite anions/hypochlorous acid (OCl − /HOCl), showing that for a selective study it is important to have an idea about the possible constituents in the studied solutions. The sensitivity of H 2 DCFDA to other RONS even in much higher concentrations was negligible. The presence of nitrites (NO 2 − ) and hydrogen peroxide (H 2 O 2 ) in PAW led predominantly to the production of peroxynitrous acid with a strong fluorescence response of H 2 DCFDA in PAW. Plasma treatment of buffered solutions led to the weak response of H 2 DCFDA. The fluorescence induced in PAW decreased after scavenging individual reactants, namely NO 2 − and H 2 O 2 , as well as by scavenging the product of the peroxynitrite forming reaction, proving that the fluorescence response of H 2 DCFDA is primarily due to the formation of ONOO − /ONOOH. A chemical kinetics analysis of post-discharge processes and the pseudo-second order reaction between H 2 O 2 and NO 2 − confirms formation of peroxynitrous acid in PAW with a rate in the order of tens of nM per second. The post-discharge evolution of the ONOOH formation rate was clearly correlated with the parallel detection of ONOO − /ONOOH by fluorescence spectroscopy using the H 2 DCFDA dye. The first study providing direct fluorescence detection of peroxynitrite/peroxynitrous acid (ONOO − /ONOOH) in plasma activated liquids correlated with the chemical kinetics of ONOOH formation.