The determinant role of ground electrode design on steering reactive species in PAW for enhanced anticancer therapy

Plasma activated water (PAW) produced via underwater bubble discharge (UBD) has attracted considerable attention due to its exceptional properties, yet limited research has been conducted on the impact of ground electrodes on PAW generation. This study utilized a UBD plasma generator with three distinct ground electrodes: a copper mesh along the side wall (GND.1), a copper foil affixed to the bottom (GND.2), and a copper wire positioned at the bottom (GND.3), to assess the characteristics of the resulting PAW. The findings indicate that the discharge intensity for GND.1 surpassed that of GND.2, which in turn exceeds that of GND.3, as a consequence of the different electric field distributions. The variations in discharge intensity led to differing concentrations of reactive species in the produced PAW, thereby affecting its anticancer efficacy. Notably, the PAW generated by GND.1 contained the highest concentrations of aqueous reactive species (NO₂⁻, H₂O₂, ONOO⁻/O₂⁻, and OH) and demonstrated the most pronounced anticancer effect, which can be linked to a substantial increase in intracellular reactive oxygen species driven by the elevated levels of aqueous reactive species. These experimental results underscore the critical role of electric field distribution within the UBD system on the properties of the resultant PAW, potentially offering avenues to enhance the anticancer capabilities of PAW and facilitate its clinical application.