Current agricultural practices are not sustainable; however, the non-thermal plasma treatment of seeds may be an eco-friendly alternative to alter macroscopic plant growth parameters. Despite numerous successful results of plasma-seed treatments reported in the literature, the plasma-treatment parameters required to improve plant growth remain elusive due to the plethora of physical, chemical, and biological variables. In this study, we investigate the optimal conditions in our surface dielectric barrier discharge (SDBD) setup, using a parametric study, and attempt to understand relevant species in the plasma treatment using in situ Fourier transform infrared (FTIR) absorption spectroscopy. Our results suggest that treatment time and voltage are key parameters for accelerated germination; however, no clear conclusion on causative agents can be drawn.

We study the bactericidal efficacy of surface dielectric barrier discharge low-temperature plasma treatments, powered by nanosecond high voltage pulses. We achieve \(\sim \)4-log reduction in Escherichia coli population, after 10 min treatments, at a distance of 1.5 cm from the plasma surface. To investigate the reactive oxygen and nitrogen species (RONS) responsible for the bactericidal effect, we employ in-situ fourier transform infrared (FTIR) spectroscopy to measure a selection of relevant species, such as O\(_3\), NO\(_2\), N\(_2\)O and N\(_2\)O\(_5\). The measurements are taken under various relative humidity conditions to replicate the bacteria treatment environment. While RONS originating from nitrogen chemistry are detected, nitric oxide (NO), a pivotal molecule in nitrate production, is absent due to the sensitivity limitations of FTIR detection. To overcome this limitation, we employ laser induced fluorescence utilizing a picosecond-pulsed laser to measure the kinetics of NO produced by the plasma. Our results show that the NO concentration is smaller than 1 ppm and primarily localized near the plasma surface, with concentrations increasing proportionally with relative humidity. Notably, at a distance of 1.5 cm from the plasma surface, at which the E. coli is treated, the concentration of NO falls below 50 ppb. Although NO is pivotal in generating secondary reactive species within the plasma, our results suggest that it does not directly contribute to the bacteria inactivation process. Instead, other molecules, such as O\(_3\), NO\(_2\), and N\(_2\)O, which are found in higher concentrations, may be responsible for the bactericidal properties observed in indirect plasma treatments.

This study presents a detailed investigation of a nanosecond-pulsed volume dielectric barrier discharge (VDBD) plasma in saturated humid air at atmospheric pressure, combining experimental diagnostics with kinetic modeling. Electric field-induced second harmonic generation (EFISH), employing a spatial filter and a picosecond laser, enabled electric field measurements with high spatial (270 µm) and temporal (28 ps) resolution at three distinct positions across the inter-electrode VDBD gap. These measurements revealed previously unobserved features and consistent differences between the discharge center and regions near the ground and high-voltage (HV) electrodes. Near the ground electrode, a higher electric field was observed prior to the first positive plasma discharge, along with an overshoot up to 50 kV cm⁻¹ during plasma breakdown, absent at the center and near the HV electrode. A sharper post-breakdown decrease and recovery in the electric field was also observed near the ground electrode, differently from the other positions. This pattern inverted during the subsequent negative discharge at the end of the HV pulse, with the higher electric field being measured near the HV electrode. To complement the electric field data, the concentrations of nitric oxide (NO) and hydroxyl radical (OH) were measured using laser-induced fluorescence (LIF), providing insight into their temporal dynamics during and after the discharge. The EFISH data served as input for a zero-dimensional kinetic model, which revealed the dynamics of both charged and neutral species, showing excellent agreement with the LIF data and validating the model accuracy. The simulation identified OH⁻, O 2 − , and O 4 − as the key negative ions responsible for the stable electric field after plasma breakdown. This research highlights the importance of understanding electric field dynamics and reactive species formation in low-temperature plasmas. Integrating EFISH and LIF data with kinetic modeling provides a robust framework to optimize plasma-based systems, improving their performance and safety in practical applications.