Evaluating the Impact of Substrate Conductivity on Nanosecond Pulsed Plasma Formation and ROSProduction in Liquid

Nonthermal atmospheric pressure plasma jets (APPJ) are of interest to various biomedical applications, including bacteria inactivation, wound healing, and cancer therapy
^{[1], [2]}
. Biologically active factors such as charged particles, electric field, and reactive oxygen and nitrogen species (RONS), are considered important agents that induce the biomedical effects. These factors can be influenced by the presence of biological materials as part of the electrode circuit. This study investigates the effect of the conductivity of the substrates on the plasma formation and the associated chemistry using a hollow needle-to-ring electrode configuration. Ultrapure water, sodium chloride (NaCl) solutions and phosphate-buffered saline (PBS) solution are used as the substrate. Driven by 200 ns, 9 kV pulses at 2 kHz, a helium ns-APPJ is generated between the hollow needle electrode and the liquid surface. The charges delivered to the substrates are evaluated by jet current measurements and compared among different substrates. Spatiotemporally resolved optical emission spectroscopy was employed to evaluate the effect of the substrate conductivity on the plasma jet formation, gas temperature, and OH(A) production. In addition, measurements of the H
2
O
2
production in the liquid were used to determine the OH concentration in liquid. An equivalent circuit model during the plasma establishment is also discussed.