Liquid Droplets in Contact With Cold Non-Equilibrium Atmospheric Pressure Plasmas

Recently, cold, non-equilibrium atmospheric pressure plasmas (CAPs) and their active chemistry have been extensively investigated to the benefit of a wide array of applications such as biomedical and industrial applications mainly in the area of materials processing and chemical synthesis, amongst many others. In general, these plasmas operate at standard conditions (i.e. 1 atm, 300K), are small (∼ cm) and rather simple to operate in comparison to other plasmas. Their complex chemistry gives rise to a wide array of both stable and transient reactive species: such as O3, H2O2, OH and NOx, next to charged species and (V)UV-radiation. This chemistry is the reason for their wide spread application and has already found many industrial applications from waste water treatment, stain free detergents and industrial scale production of oxidants. In recent years, bactericidal effects of CAPs gained increasing attention for applications such as dermatology, disinfection, dentistry and cancer treatment or stimulated blood coagulation. This paper aims to highlight recent research into new biological applications for complex mission scenarios involving humans in remote locations using CAPs for disinfection, bleaching or wound healing. Results using radiofrequency plasma jets for the inactivation of Pseudomonas aeruginosa are summarized, highlighting the importance of liquid plasma interactions. Work with such a CAP paved the way for a promising application in the field of biomedical applications presented here. It involves surface barrier discharges which can be used to treat larger surfaces compared to jets. Their physical construction, using floating or contained electrodes, offer a convenient way of controlling electrical current on a large scale, 3D treatment of both conducting and insulating surfaces with minimal heating. These devices may be tailored to specific skin treatments, allowing fast and effective treatment of larger skin surfaces while following the shape of the skin. This might reduce the need for bactericidal agents and would be a valuable application to assist humans in remote locations. These emerging technologies could be essential both for human health care under extreme conditions, as well as for research itself (sterilisation of tools and large areas, etc.). Especially in the absence of abundant resources (antibiotic agents, disinfectants and the like) alternative approaches to support humans in isolated locations have to be developed. Applications based on a good understanding of plasma chemistry would empower health care under extreme conditions to efficiently use and manage in situ resources. Their low mass, compact size, low power consumption and high reliability could make them essential use under extreme conditions.