Microplasma Bubbles: Reactive Vehicles for Biofilm Dispersal

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Abstract
Interactions between effects generated by cold atmospheric-pressure plasmas (CAPPs) and water have been widely investigated water purification, chemical and nanomaterial synthesis, and more recently, medicine and biotechnology. Reactive oxygen and nitrogen species (RONS) play critical roles in transferring the reactivity from gas plasmas to solutions to induce specific biochemical responses in living targets, e.g. pathogen inactivation and biofilm removal. While this approach works well in a single-organism system at lab scale, integration of plasma-enabled biofilm removal into complex real-life systems, e.g. large aquaculture tanks, is far from trivial. This is because it is difficult to deliver sufficient concentrations of the right kind of species to biofilm-covered surfaces while carefully maintaining a suitable physiochemical environment that is healthy for its inhabitants, e.g. fish. In this work, we show that underwater microplasma bubbles (generated by a microplasma-bubble reactor that forms a dielectric barrier discharge (DBD) at the gas-liquid interface with the aplied voltage of 4.0 kV) act as transport vehicles to efficiently deliver reactive plasma species to target biofilm sites on artificial and living surfaces while keeping healthy water conditions in a multi-species system. Thus-generated air microplasma bubbles and plasma activated water (PAW) both can effectively reduce existing pathogenic biofilm load, by ~83% and 60% respectively after 15 min-discharge at 40 W, and prevent any new biofilm from forming. Generation of underwater microplasma bubbles in a custom-made fish tank for less than a minute per day (20 seconds per-time, twice daily) can introduce sufficient quantities of RONS into PAW to reduce biofilm infected area by ~80-90% and imrpove the health status of Cichlasoma synspilum × Cichlasoma citrinellum blood parrot cichlid fish. Species generated include hydrogen peroxide, ozone, nitrite, nitrate and nitric oxide. Using mimicked chemical solutions, we show that plasma-induced nitric oxide acts as a critical bioactive species that triggers the release of cells from biofilm and their inactivation.
Funding Information
  • Australian Research Council
  • National Natural Science Foundation of China (51877184)
  • Queensland University of Technology

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