Low-flow argon cold atmospheric plasma jet for E. coli inactivation and PAW fingerprinting

Abstract Chemical disinfectants are effective in many settings, yet they can leave persistent residues and contribute to environmental contamination pathways. In parallel, the growing prevalence of antibiotic-resistant pathogens increases the demand for alternative decontamination strategies. Cold atmospheric pressure plasma (CAP) represents a promising physical approach because reactive species are generated locally without requiring persistent chemical biocides. Here, a portable low-flow argon plasma jet prototype (12 kV AC, 60- 130 kHz, argon 1 L/min) is evaluated for direct antibacterial surface activity and for plasma-activated water (PAW) fingerprinting. In an agar diffusion assay, direct plasma exposure produced a significant time-dependent inactivation of Escherichia coli DSM 613, with inhibition zone diameters increasing from 6.3 ± 1.2 mm (1 min) to 12.5 ± 1.0 mm (5 min; n = 6) at 5 mm distance. Under identical geometry, the reference device kINPen MED yielded larger inhibition zones (10.0 ± 0.9 mm to 22.3 ± 2.5 mm), but operated at an approximately fivefold higher process gas flow (5 L/min). In addition, PAW generated by both systems was characterized by pH, electrical conductivity, and redox potential as a chemical fingerprint. The prototype induced stronger changes in these sum parameters for selected matrices. These PAW parameters are reported as process markers for device comparison and optimization rather than as direct evidence of antibacterial efficacy in the liquid phase.