Effect of discharge polarity on the propagation of atmospheric-pressure helium plasma jets and the densities of OH, NO, and O radicals

Plasma-enhanced microbial electrolytic disinfection: Decoupling electro- and plasma-chemistry in plasma-electrolyzed oxidizing water using ion-exchange membranes

Pathogenic microorganisms pose a global threat to public health and environment. Common antibacterial chemicals produce toxic residues, inevitably harming the environment. Electrolyzed oxidizing water (EOW), a promising environment-friendly alternative disinfectant, still lacks effective production processes, sufficient bactericidal efficacy and stability, while the enabling physico-chemical mechanisms remain unclear. Here, we report, for the first time, an effective hybrid plasma electrochemical EOW production process and reveal the mechanisms by combining nonthermal plasmas and a two-chamber electrochemical cell separated by a cation exchange membrane (CEM) for decoupling the chemical reactions during the plasma treatment of water. Experimental results demonstrate that combined chlorine (chloramine) was the main chlorine product in the plasma-enhanced EOW (P-EOW) without a membrane, owing to the consumption of free chlorine  (Cl₂, HOCl, ClO^-) by plasma-generated reactive nitrogen species. With a CEM in the plasma electrolysis system and through controlling the plasma discharge polarity, the production of free chlorine and other reactive species can be selectively controlled, with the highest concentration of free chlorine obtained in the negative plasma-enhanced EOW (NP-EOW). According to the transportation of cations by the CEM, the high concentrations of free chlorine may be attributed to the higher consuptions of H⁺ in cathode cell of negative plasma. The study of antibacterial ability of EOW produced under different conditions revealed that Staphylococcus aureus cells were best inactivated by the NP-EOW with CEM, which is mainly attributed to the higher concentration of free chlorine. This study demonstrates the feasibility of plasma-enhanced microbial electrolytic disinfection and offers new insights into the fundamental aspects of P-EOW chemistries for the future development of sustainable, efficient, and cost-effective multipurpose sustainable chemical technologies for water research and treatment.

Quantification of surface charging memory effect in ionization wave dynamics

The dynamics of ionization waves (IWs) in atmospheric pressure discharges is fundamentally determined by the electric polarity (positive or negative) at which they are generated and by the presence of memory effects, i.e. leftover charges and reactive species that influence subsequent IWs. This work examines and compares positive and negative IWs in pulsed plasma jets (1 [Formula: see text]s on-time), showing the difference in their nature and the different resulting interaction with a dielectric BSO target. For the first time, it is shown that a surface charging memory effect is produced, i.e. that a significant amount of surface charges and electric field remain in the target in between discharge pulses (200 [Formula: see text]s off-time). This memory effect directly impacts IW dynamics and is especially important when using negative electric polarity. The results suggest that the remainder of surface charges is due to the lack of charged particles in the plasma near the target, which avoids a full neutralization of the target. This demonstration and the quantification of the memory effect are possible for the first time by using an unique approach, assessing the electric field inside a dielectric material through the combination of an advanced experimental technique called Mueller polarimetry and state-of-the-art numerical simulations.

Cold Atmospheric Pressure Plasma (CAP) as a New Tool for the Management of Vulva Cancer and Vulvar Premalignant Lesions in Gynaecological Oncology

Vulvar cancer (VC) is a specific form of malignancy accounting for 5–6% of all gynaecologic malignancies. Although VC occurs most commonly in women after 60 years of age, disease incidence has risen progressively in premenopausal women in recent decades. VC demonstrates particular features requiring well-adapted therapeutic approaches to avoid potential treatment-related complications. Significant improvements in disease-free survival and overall survival rates for patients diagnosed with post-stage I disease have been achieved by implementing a combination therapy consisting of radical surgical resection, systemic chemotherapy and/or radiotherapy. Achieving local control remains challenging. However, mostly due to specific anatomical conditions, the need for comprehensive surgical reconstruction and frequent post-operative healing complications. Novel therapeutic tools better adapted to VC particularities are essential for improving individual outcomes. To this end, cold atmospheric plasma (CAP) treatment is a promising option for VC, and is particularly appropriate for the local treatment of dysplastic lesions, early intraepithelial cancer, and invasive tumours. In addition, CAP also helps reduce inflammatory complications and improve wound healing. The application of CAP may realise either directly or indirectly utilising nanoparticle technologies. CAP has demonstrated remarkable treatment benefits for several malignant conditions, and has created new medical fields, such as “plasma medicine” and “plasma oncology”. This article highlights the benefits of CAP for the treatment of VC, VC pre-stages, and postsurgical wound complications. There has not yet been a published report of CAP on vulvar cancer cells, and so this review summarises the progress made in gynaecological oncology and in other cancers, and promotes an important, understudied area for future research. The paradigm shift from reactive to predictive, preventive and personalised medical approaches in overall VC management is also considered.

The generation and transport of reactive nitrogen species from a low temperature atmospheric pressure air plasma source

The reactive chemical species generated by non-equilibrium plasma under atmospheric pressure conditions are key enablers for many emerging applications spanning the fields of biomedicine, manufacturing and agriculture. Despite showing great application potential, insight in to the underpinning reactive species generation and transport mechanisms remains scarce. This contribution focuses on the spatiotemporal behaviour of reactive nitrogen species (RNS) created and transported by an atmospheric pressure air surface barrier discharge (SBD) using both laser induced fluorescence and particle imaging velocimetry measurements combined with experimentally validated numerical modelling. It was observed that highly reactive species such as N are confined to the discharge region while less reactive species such as NO, NO2 and N2O closely followed the induced flow. The concentration of key RNS was found to be in the 10-100 ppm range at a position of 25 mm downstream of the discharge region. A close agreement between the experimental and computational results was achieved and the findings provide a valuable insight in to the role of electrohydrodynamic forces in dictating the spatiotemporal distribution of reactive chemical species beyond the plasma generation region, which is ultimately a key contributor towards downstream treatment uniformity and application efficacy.

Electrical, Thermal and Optical Parametric Study of Guided Ionization Waves Produced with a Compact μs-Pulsed DBD-Based Reactor

Atmospheric pressure guided ionization waves (GIWs) that are driven by ns/μs-pulsed high voltages, are promising tools in the biomedical field allowing for the effective production of reactive species and metastables without thermal damages of the specimens that are exposed. In most cases, plasma is produced in noble gases using dielectric barrier discharge (DBD) devices of more-or-less sophisticated geometries. In this study, a compact low-cost DBD reactor of very simple geometry is presented. It is fed with pure helium and driven by positive μs-pulsed high voltage (amplitude: 4.5–8 kV, pulse width: 1–10 μs) of audio frequencies (5–20 kHz), while it operates consistently for long time periods in a wide range of conditions. The produced plasma exhibits propagation lengths up to 4 cm and rich chemical reactivity is established outside the reactor, depending on the device’s experimental parameters. Besides, the dielectric tube’s temperature during plasma operation is an important factor, which is linked to the plasma characteristics. This temperature and its variations are thoroughly investigated herein, along with GIWs electrical features versus the electrical parameters of the pulsed power supply. Accordingly, it is demonstrated that not all of the operational windows are adequate for thermal-free operation and suitable operating conditions of this system are proposed for diverse applications, such as biomedical (low gas temperature is a prerequisite) and surface treatments of solid materials (low temperatures are not required).