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In this study, a microbubble‐enabled plasma reactor driven by a nanosecond‐pulsed generator was developed to provide an effective means for transferring highly reactive plasma species into liquids for plasma‐activated water (PAW) production. The physicochemical characteristics of PAW at different temperatures were evaluated, and the corresponding antimicrobial effects of PAW against Escherichia coli cells were investigated. Results show that the microbubble‐enabled PAW at a lower temperature (10°C) had the highest antimicrobial activity, resulting in a 2.43 ± 1.02‐log10 reduction of E. coli in PAW. The excellent energy efficiency of the total reactive oxygen and nitrogen species production in PAW is 10.37 g kW−1 h−1. Overall, this study provides much‐needed insights into the microbubble‐enabled plasma chemistries for optimizing the biochemical activity of PAW. [ABSTRACT FROM AUTHOR]

Aims: This study aimed to compare the efficacy of plasma‐activated water (PAW) generated by two novel plasma reactors against pathogenic foodborne illness organisms. Methods and results: The antimicrobial efficacy of PAW produced by a bubble spark discharge (BSD) reactor and a dielectric barrier discharge‐diffuser (DBDD) reactor operating at atmospheric conditions with air, multiple discharge frequencies and Milli‐Q and tap water, was investigated with model organisms Listeria innocua and Escherichia coli in situ. Optimal conditions were subsequently employed for pathogenic bacteria Listeria monocytogenes, E. coli and Salmonella enterica. DBDD‐PAW reduced more than 6‐log of bacteria within 1 min. The BSD‐PAW, while attaining high log reduction, was less effective. Analysis of physicochemical properties revealed that BSD‐PAW had a greater variety of reactive species than DBDD‐PAW. Scavenger assays designed to specifically sequester reactive species demonstrated a critical role of superoxide, particularly in DBDD‐PAW. Conclusions: DBDD‐PAW demonstrated rapid antimicrobial activity against pathogenic bacteria, with superoxide the critical reactive species. Significance and impact of study: This study demonstrates the potential of DBDD‐PAW produced using tap water and air as a feasible and cost‐effective option for antimicrobial applications, including food safety. [ABSTRACT FROM AUTHOR]

The interactions between plasma‐generated excited particles and water play an integral role in sustainable degradation of pharmaceutical compounds, improving aerobic respiration of activated sludge, and efficient removal of microorganisms from water, and are fundamental to the intentional transfer of reactivity from plasmas to biological solutions for such medical applications as cancer treatment and wound healing. The physical and chemical mechanisms that govern this transfer of reactivity are complex, and include concomitant generation and consumption of species in the gas and liquid phases, and at the interface. As such, it is challenging to predict the quantities of biologically‐active radicals and molecules in liquid phase from gas phase measurements alone. Rapid and accurate quantification of reactive species, such as OH radicals and H2O2 molecules within the liquid phase and their link to specific biological effects is therefore critical for medical applications of plasma‐activated solutions. Using a simple, low‐cost method for trapping and stabilization of OH radicals by means of salicylic acid, this work seeks to provide further insights into the physics and chemistry of generation of OH radicals within the liquid phase, and integrate these findings with decontamination outcomes for four commonly used processing gases. [ABSTRACT FROM AUTHOR]

Atmospheric-pressure plasma and TiO2 photocatalysis have been widely investigated separately for the management and reduction of microorganisms in aqueous solutions. In this paper, the two methods were combined in order to achieve a more profound understanding of their interactions in disinfection of water contaminated by Escherichia coli. Under water discharges carried out by microplasma jet arrays can result in a rapid inactivation of E. coli cells. The inactivation efficiency is largely dependent on the feed gases used, the plasma treatment time, and the discharge power. Compared to atmospheric-pressure N2, He and air microplasma arrays, O2 microplasma had the highest activity against E. coli cells in aqueous solution, and showed >99.9% bacterial inactivation efficiency within 4 min. Addition of TiO2 photocatalytic film to the plasma discharge reactor significantly enhanced the inactivation efficiency of the O2 microplasma system, decreasing the time required to achieve 99.9% killing of E. coli cells to 1 min. This may be attributed to the enhancement of ROS generation due to high catalytic activity and stability of the TiO2 photocatalyst in the combined plasma-TiO2 systems. Present work demonstrated the synergistic effect of the two agents, which can be correlated in order to maximize treatment efficiency. [ABSTRACT FROM AUTHOR]

Plasma medicine is a relatively new field that investigates potential applications of cold atmospheric-pressure plasmas in bioengineering, such as for bacterial inactivation and degradation of organic molecules in water. In order to enunciate mechanisms of bacterial inactivation at molecular or atomic levels, we investigated the interaction of atmospheric-pressure air microplasmas with amino acids in aqueous solution by using high-resolution mass spectrometry (HRMS). Results show that the oxidation effect of plasma-induced species on the side chains of the amino acids can be categorized into four types, namely hydroxylation, nitration, dehydrogenation and dimerization. In addition, relative activities of amino acids resulting from plasma treatment come in descending order as follows: sulfur-containing carbon-chain amino acids > aromatic amino acids > five-membered ring amino acids > basic carbon-chain amino acids. Since amino acids are building blocks of proteins vital to the growth and reproduction of bacteria, these results provide an insight into the mechanism of bacterial inactivation by plasma. [ABSTRACT FROM AUTHOR]

The chemistry, antimicrobial efficacy and energy consumption of plasma-activated water (PAW) was optimized by altering the discharge frequency, ground-electrode configuration, gas flow rate and initial water conductivity for two reactor configurations, i.e., air pin-to-liquid discharge and air plasma-bubble discharge in water. The ratio of NO 2 − and NO 3 − formation was altered to optimise the antimicrobial effects of PAW, tested against two Gram-negative bacteria. An initial solution conductivity of 0.2 S·m−1 and 2000-Hz discharge frequency with the ground electrode positioned inside the pin reactor showed the highest antimicrobial effect resulting in a 3.99 ± 0.13-log 10 reduction within 300 s against Escherichia coli and 5.90 ± 0.24-log 10 reduction within 240 s for Salmonella Typhimurium. An excellent energy efficiency of reactive oxygen and nitrogen species (RONS) generation of 10.1 ± 0.1 g·kW−1·h−1 was achieved. Plasma-activated water (PAW) is deemed as an eco-friendly alternative to chemical disinfection because its bactericidal activity is temporary. Optimizing the design and operation of PAW reactors to achieve high inactivation rates of more than 5-log 10 reductions, as demonstrated in this work, will support the industrial application of this technology and the scaleup at industrial level. • Increasing discharge frequency from 1000 to 2000 Hz improved the antimicrobial characteristics of PAW by the pinreactor • Increasing initial liquid conductivity in the pin reactor increased the bacterial inactivation to 1.74–4.4-log 10 reduction • Ground electrode inside the pin reactor caused higher E. coli (3.99-) and S. Typhimurium (5.90-log 10 reduction) inactivations • Altering ground-electrode position from inside to outside the bubble reactor changed the NO 2 −/ NO 3 − ratio from 0.92 to 2.69 • The optimal PAW configuration, achieving more than 5-log reduction of S. Typhimurium , was the pin-to-liquid discharge [ABSTRACT FROM AUTHOR]