Because of their unique features, non-thermal plasmas have recently been considered an attractive technology for various applications, including biomedicine. In-depth studies on the interaction of non-thermal plasmas with microorganisms, however, have mainly focused on bacteria, with only little attention given to more complex eukaryotic cells. Interestingly, the effect and mechanism of interaction between plasmas and living cells seems somehow dependent on the configuration and operational conditions of plasma production. In this paper, we report our observations on the effects of non-thermal air plasma generated by a DBD on cell motility, viability, and morphology of a variety of eukaryotic microalgae in aqueous environments, with three dinoflagellates (unarmored and armored) and a diatom as major targets. The effects on motility and viability depended on the time of exposure to plasma and the species of microalgae. More importantly, a strong decrease in pH in a variety of aqueous samples (algal cultures, marine and freshwater culture media, and deionized water) was observed after exposure to plasma, and was hypothesized as the mechanism leading to cell death. The hypothesis was strongly supported by observations using scanning-electron microscopy, following an intentional decrease in pH (effected by addition of acid), in which we observed morphological damage identical to that induced by exposure to plasma.
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