Atmospheric-pressure plasma-droplet treatment system
: focus on aerosolised bacteria and remote delivery of reactive species

  • David Rutherford

Student thesis: Doctoral Thesis


This thesis presents an experimental study of a novel non-thermal atmospheric-pressure gas plasma with controlled liquid droplet flow as an efficient source of reactive species that can influence fundamental chemistries in many applications. The electrical discharge is ignited within the confined geometry of a cylindrical quartz tube that allowed for small liquid droplets entrained in the gas flow to pass through the plasma region only once. Neon was used to generate the droplets from deionised water or a buffered solution and additional helium transported the droplets from the nebuliser through the plasma. A diffuse, glow-like discharge formed that remained ignited during droplet transport. Droplets that enter the plasma contribute to the formation of reactive species and survive the treatment without complete evaporation. This observation paved the way for attempts to expose bacteria-loaded droplets to the same treatment. When collected in the presence of a hydrogen peroxide scavenger, plasma treatment did not affect cell viability or growth kinetics. A biomarker of lipid peroxidation was detected, suggesting cell interaction with plasma-generated species delivered into the droplet over short timescales i.e. droplet transit time through the plasma region. Due to the omission of oxygen and nitrogen from the plasma, a vast proportion of RONS that are reported in the plasma-liquid literature cannot be generated, therefore simplifying the chemistry. Hydroxyl radical is thought to feature in the onset of cellular oxidative stress and the species is known to be generated from plasma-liquid interactions. The radical was detected in both the gas and liquid phases from the plasma treatment of droplets and remained chemically active far from the core plasma region. Hydrogen peroxide is a well-known biocide generated from plasma-liquid interactions and was detected in the plasma-treated droplet collection liquid. These results suggest the new technique can remotely apply reactive species contained in plasma-activated droplets or bulk liquid to a target that never comes in direct contact with the plasma itself. This has the potential to be able to influence biological systems in a controlled way by fine-tuning the chemistry generated from the interaction between non-equilibrium plasma and low volume liquid droplets.
Date of AwardAug 2017
Original languageEnglish
SupervisorPaul Maguire (Supervisor), DAVID MCDOWELL (Supervisor) & Davide Mariotti (Supervisor)


  • Atmospheric-pressure gas plasma
  • Glow discharge
  • Low-volume liquid droplets
  • Hydroxyl radical
  • Hydrogen peroxide
  • Plasma medicine
  • Antibacterial treatment

Cite this