Andrew Robert Gibson

This study introduces plasma‐triggered liposomal cargo release as a promising new approach for externally activatable drug delivery systems (DDS). The metal complex [Pt(1 S ,2 S ‐diaminocyclohexane)(4,7‐dimethoxy‐1,10‐phenanthroline)] ²⁺ ( 1 ) was encapsulated into L‐α‐phosphatidylcholine liposomes. Liposomal formulations of 1 were treated with a microscale atmospheric pressure plasma jet (cold atmospheric plasma, CAP), and cargo release was monitored with inductively coupled plasma optical emission spectroscopy (ICP‐OES). Moreover, the cytotoxic activity of 1 and its liposomal formulation treated with CAP for different times was analyzed via cell viability assays and calibrated to control experiments. Liposomal encapsulation enhances cytotoxicity and protects the metal complex from plasma‐induced decomposition, thereby offering a novel, enhanced DDS that overcomes the limited penetration depth of plasma‐generated short‐lived RONS as a direct antiproliferative modality.

In-liquid plasma electrolysis refers to the ignition of a plasma in a thin vapor layer surrounding a solid electrode immersed in a liquid electrolyte and its associated processes. Over the last century, this phenomenon has been described under various names and is frequently denoted as Contact Glow Discharge Electrolysis. Previous works could show that the plasma might not solely consist of a glow that extends through the entire vapor layer, as the name implies, but consists of multiple filamentary discharges. Building on our previous work on the statistical evaluation of such discharges (J. Phys. D: Appl. Phys. 58 (2025) 215204), here we study the discharge properties, such as their general appearance, gas temperature, electron density, current density, electron production mechanism, and the discharge voltage, using optical emission spectroscopy, scanning electron microscopy imaging, and electrolyte potential measurements. Our results indicate that the discharges do not solely consist of glow discharges. Instead, the possible co-existence of other discharges, such as arcs and sparks, is discussed.

Microdischarges formed in bubbles immersed in liquids are of interest for materials synthesis and chemical conversion applications in the frame of plasma-driven electrochemistry. A key challenge associated with controlling such processes is the limited understanding of the gas-phase chemical kinetics in these microdischarges. Due to their large electron densities, and high gas temperatures, both electron and gas temperature-driven chemistry are likely to be important. Here, a 0-D modeling approach, informed by experimental measurements, is used to study the chemical kinetics in these systems. A new reaction scheme is developed for microdischarges in water vapor, including reactions for both high electron density, and high gas temperature regimes. Microdischarges formed during plasma electrolytic oxidation are used as a test case, however, the key results are expected to be transferable to other plasma electrolysis systems with similar properties. Experimentally measured power densities are used as input to the 0-D model, together with estimates of temperatures and gas pressures within the gas bubble. Comparison of measured and simulated electron densities shows good agreement, given the limitations of both model and experiment. In the base case microdischarge, H ₂ O is found to be highly dissociated during the period of peak power density, with H and O making up the majority of the neutral gas in the bubble. The maximum ionization degree is around 0.31%, and the electronegativity during the period of peak electron density is found to be low. Species formation and reaction pathways are analyzed under variation of the neutral gas temperature from 2000 K to 6000 K. At all temperatures, electron, ion, and neutral reactions with high threshold energies are found to be important for the overall chemical kinetics.

This study is focused on measuring the densities of the excited molecular oxygen species, O 2 ( a 1 Δ g ) and O 2 ( b 1 Σ g + ) , produced in a COST atmospheric pressure plasma jet using a helium–oxygen mixture. Knowledge of the ozone density is critical for measurements because of its high quenching rate of these species. Additionally, O 2 ( a 1 Δ g ) is difficult to measure due to its low emission intensity and sensitivity to background interference in the plasma region. Therefore, a flow cell was used to enhance signal detection in the effluent region. To validate the measurements and improve understanding of reaction mechanisms, results were compared with two simulation models: a pseudo-one-dimensional plug flow simulation and a 2D fluid simulation. The plug flow simulation provided an effective means for estimating species densities, with a fast computation time. The 2D simulation offered a more realistic description of the flow dynamics, which proved critical to correctly describe the experimental trends. However, it requires long computation times to reach an equilibrium state in the flow cell. Otherwise, it leads to discrepancies to the experimental data. Further discrepancies arose from an overestimation of the ozone density from the models, as validated from the O 2 ( b 1 Σ g + ) density measurements. Optimizing the reaction rate coefficients for the effluent region might improve the agreement with the experimental results. Despite these limitations, both simulations aligned reasonably well with experimental data, showcasing the well validated plasma chemistry of the models, even for complicated effluent geometries.

Reactive species produced by atmospheric pressure plasma jets have high application potential in the fields of biomedicine and surface processing. An extensive validation between the simulation results in this work and measurement data from various research groups is carried out in order to reliably understand the complicated chemical kinetics defining the reactive species densities. Atomic oxygen densities in parallel plate radio frequency driven He/O₂ micro-scaled atmospheric pressure plasma jets (μAPPJs) have been measured in the literature by several research groups with different methods including: two-photon absorption laser induced fluorescence (TALIF) spectroscopy and optical emission spectroscopy (OES)-based methods. These measurement data with a variation of the absorbed power, the He gas flow rate and the O₂ mixture ratio are simulated in this paper with a zero-dimensional (0-D) plasma-chemical plug-flow model coupled with a two-term Boltzmann equation solver. The simulated atomic oxygen densities agree well with most of the measured ones. Specifically, good agreement is achieved between the simulations and most of the TALIF measurements over a range of operating conditions. Our model prediction accuracy relative to these TALIF measurements is quantified by the percentage error between the measured and simulated atomic oxygen densities. An approximate normal distribution is observed in the histogram plot of the percentage error, and the mean is close to zero. The mean is shifted positively and negatively in the case of removing a dominant atomic oxygen gain and loss reaction channel, which implies the underestimation and overestimation of the simulation results relative to the measurement data, respectively. This indicates that proper incorporation of the dominant reaction channels in the simulations plays a key role in the model prediction accuracy.

Plasma liquid interactions are important for a range of applications. For these, H₂O₂ and OH represent two key reactive species, whose concentrations in liquids need to be controlled for effective application outcomes. Here, a combination of gas and liquid simulations is used to study the concentration profiles of H₂O₂ and OH in water treated by a radio-frequency-driven plasma jet, with a glass capillary between the electrodes, operated in He with admixtures of water vapour. Simulations are compared with measured H₂O₂ concentrations and found to be in good qualitative agreement as plasma power and water admixture are varied. Simulation results show that the concentration profiles of H₂O₂ in the liquid are mainly determined by transport, while those of OH are limited by reactions with H₂O₂, which consumes OH. For a given plasma operating condition, the concentration and penetration depth of H₂O₂ increase with plasma treatment time, while those of OH tend to decrease because of the increasing H₂O₂ concentration. Plasma power, water vapour admixture, and the distance between the jet and the liquid surface all allow for the concentrations of H₂O₂ and OH to be controlled. The OH delivered from the gas phase to the liquid, and its concentration within the liquid are strongly dependent on the reaction pathways occurring in the effluent region, such that the trends in OH density at the end of the plasma region differ from those in the liquid. While the concentration of OH in the liquid is always much lower than that of H₂O₂, the ratio of the two species can be controlled over orders of magnitude by varying water admixture and power. The highest selectivity to OH is at low water admixtures, low powers and short treatment times, while the highest selectivity to H₂O₂ is at high water admixtures, high powers and long treatment times.

Plasma electrolytic oxidation (PEO) is a technique used to create oxide-ceramic coatings on lightweight metals, such as aluminium, magnesium, and titanium. PEO is known for producing coatings with high corrosion resistance and strong adhesion to the substrate. The process involves generating short-lived microdischarges on the material surface through anodic dielectric breakdown in a conductive aqueous solution. To investigate single microdischarges (SMDs) during PEO, a SMD setup was developed, where the active anode surface is reduced to the tip of a wire with a diameter of 1 mm. In this work the focus is on the effect of electrolyte concentration, anode material, and electrical parameters on the microdischarges. The electrolyte is composed of distilled water with varying concentrations of potassium hydroxide (0.5–4 g l⁻¹). High-speed optical measurements are conducted to gain insights into the formation and temporal evolution of individual microdischarges and the induced gas bubble formation. Optical emission spectroscopy is used to estimate surface and electron temperatures by fitting Bremsstrahlung and Planck’s law to the continuum spectrum of the microdischarges. To evaluate the impact of the microdischarges on coating morphology, the resulting oxide layers on the metal tips are analysed using scanning electron microscopy. The study demonstrates that microdischarge behaviour is significantly influenced by the substrate material, treatment time, and electrolyte concentration, all of which impact the coating morphology. Under the conditions studied in this work, aluminium exhibits longer microdischarge and bubble lifetimes, with fewer cracks on the top layer of the coating, whereas titanium showed faster, shorter-lived bubbles due to more rapid microdischarge events.

In-liquid plasma electrolysis refers to the ignition of a plasma in a thin vapor layer surrounding a solid electrode immersed in a liquid electrolyte and its associated processes. Over the last century, this phenomenon has been described under various names and is frequently denoted as Contact Glow Discharge Electrolysis. Previous works could show that the plasma might not solely consist of a glow that extends through the entire vapor layer, as the name implies, but consists of multiple filamentary discharges. Building on our previous work on the statistical evaluation of such discharges (J. Phys. D: Appl. Phys. 58 (2025) 215204), here we study the discharge properties, such as their general appearance, gas temperature, electron density, current density, electron production mechanism, and the discharge voltage, using optical emission spectroscopy, scanning electron microscopy imaging, and electrolyte potential measurements. Our results indicate that the discharges do not solely consist of glow discharges. Instead, the possible co-existence of other discharges, such as arcs and sparks, is discussed.

The presented work investigates a surface dielectric barrier discharge (SDBD) operated dry synthetic air as the working gas using a combination of experimental measurements and simulations. The primary objective is to characterize the production and consumption dynamics of reactive oxygen and nitrogen species to enhance the understanding of their formation and facilitate control of the discharge for applications. Densities of O3, NO2, and N2O5 are measured under varying gas flow rates, utilizing optical absorption spectroscopy as the diagnostic method. A semi-empirical chemical kinetics model is developed based on a compilation of reactions from previous studies on similar types of discharges. The results reveal two previously known and distinct operating modes, with a mode transition occurring between the modes as the flow rate is varied. The results indicate the dependency of the mode transition on the density of sufficiently vibrationally excited nitrogen molecules, which is represented in the model by an increased vibrational temperature at lower gas flow rates. Furthermore, key reactions responsible for the production and consumption of ozone and nitrogen oxides are identified, providing insight into the importance of macroscopic parameters, such as gas temperatures and different time constants, that influence the non-linear balance of these reactions.