Examining the effects of plasma treatment on E. coli with single-cell impedance flow cytometry

The bactericidal effects of low-temperature plasmas (LTPs) have been well-documented and are the result of the intricate cocktail of reactive species delivered during plasma treatment [1]. Identifying specific inactivation pathways has proven difficult, however, considering the complex plasma-induced chemistry in the liquid phase and poorly-understood interactions between plasma-generated reactive species and biological targets [2]. Here, single-cell impedance flow cytometry (IFC), a novel diagnostic in the field of LTPs, is employed to comprehensively examine the cellular response to plasma treatment. The utility of single-cell IFC is primarily derived from the frequency-dependence of the impedance signal of bacteria. This allows for the dielectric response of each subcellular layer to be probed in an expedient and label-free manner. Experimental results will be shared highlighting the variable impedance response between E. coli treated directly in solution with a kINPen plasma jet, and indirectly with plasma-activated water from a thoroughly-characterized reactor [3]. Additional techniques applied experimentally to extend the operating frequency range of the instrument, and to calibrate the impedance signal to extract the dielectric parameters of plasma-treated cells will be discussed. Possible mechanisms for the observed changes in the permittivity and conductivity of E. coli after plasma treatment will also be considered. Finally, results from a COMSOL model of the single-cell IFC instrument will be compared to experimental results, with a specific focus on the shortcomings of conventional theoretical approaches for analyzing the dielectric properties of bacteria.

[1] D. B. Graves J. Phys. D: Appl. Phys. 45(263001), 2012.

[2] K. Stapelmann et al., J. Appl. Phys. 135(160901), 2024

[3] R. Agus et al., Chemical Engineering Journal 486(149915), 2024.