22 nd I nternational Symposium on Plasma Chemistry July 5-10, 2015; Antwerp, Belgium P-III-10-17 1 DC corona discharges in air for bio-decontamination of glass surface from Escherichia coli Z. Kovalova 1,2 , B. Tarabová 1 , M. Leroy 2 , E. Odic 2 , M.J. Kirkpatrick 2 and Z. Machala 1 1 Faculty of Mathematics, Physics and Informatics, Comenius University, 842 84 Bratislava, Slovakia 2 Group of Electrical Engineering Paris GeePs, CentraleSupélec, CNRS UMR 8507, UPSud and UPMC Sorbonne Université 91192 Gif-sur-Yvette, France Abstract: Corona discharges in air in positive and negative polarity were used for bio- decontamination of glass surfaces from planktonic Escherichia coli and its biofilm. In order to enhance the bactericidal effect of the plasma, water was electrosprayed from a hollow electrode onto the sample for either half or the entire treatment time. The best bio- decontamination efficiency of 4.5 log was achieved with electrospray during 20 min of treatment by positive streamer corona. Our first results on E. coli biofilm treatment are presented and a possible loss of biofilm biomass is measured. In order to better understand the processes of bacteria inactivation, the electrosprayed water was chemically analysed. Keywords: Escherichia coli, Bacterial biofilm, Corona discharge, Bio-decontamination, Electrospray 1. Introduction Bacterial contamination of surfaces is a common problem for patients in hospitals, for the food industry, water distribution systems, etc. In order to avoid using toxic chemicals to achieve desired decontamination efficiency, we need to seek for new alternative methods of decontamination. Non-thermal plasma at atmospheric pressure is well-adapted for decontamination of thermally sensitive surfaces because it produces radiation (UV, visible, IR), electromagnetic fields, excited species, radicals and various chemical products, free electrons and ions, while bulk temperature remains close to ambient. Its bactericidal effect has been previously tested on a range of bacterial species - planktonic bacteria, spores or bacterial biofilms. Electrosprayed water brings more complexity to the discharge chemistry and its interaction with bacteria. The effect of water electrospray combined with corona discharges has been previously studied in our group [1, 2] and applied to the biofilm and spore decontamination of plastic surfaces [3, 4] and to water disinfection [5, 6]. In this paper we investigate the impact of water electrospray and the effect of the convective transport of neutral species produced in the plasma from the surface of planktonic Escherichia coli. 2. Materials and methods Both positive corona (PC) and negative corona (NC) discharges in air were studied for bio-decontamination of Escherichia coli in both planktonic and biofilm form on glass surfaces. We tested the effect of water electrospray through the discharge on its bactericidal efficiency. 2.1 Experimental set-up and discharges Corona discharges at atmospheric pressure in air were generated in an experimental set-up consisting of a DC high-voltage (HV) power supply and a discharge chamber. The discharge chamber contained a sharp or a clipped hypodermic syringe needle as HV electrode opposite a grounded copper plate. Treated samples were placed on the grounded electrode, 5 mm from HV electrode. Some experiments were done with sterile distilled water electrospayed onto the sample, by pumping (with SyringePump NE-300) through a hollow clipped HV electrode. Electrical characteristics of the discharges were measured: the voltage with a Tektronix P6015A HV probe and the electrical current on a 50 Ω grounded resistor connected through a coaxial cable to a Tektronix TDS 2024 digital oscilloscope. Corona discharges of both polarities were used in point to plane configuration. Positive streamer corona (PC) was supplied with a voltage up to 9 kV and formed streamers with frequencies from 10 - 20 kHz and maximum amplitudes up to 100 mA with or without water spraying. NC was supplied with a maximum voltage of 8 kV and current pulses with frequencies from 0.5 to 2 MHz and amplitudes up to 1 mA were observed with or without water spraying. More details on the discharge experimental conditions can be found in [4]. 2.2 Bacterial samples In all experiments we used glass cover slides (2×2 cm) as substrates for the bacterial samples. Three different Escherichia coli strains were used for this study: DH1, BW25113 and BW25113 with plasmid F (F+). In the case of planktonic bacteria, a frozen aliquot (DH1) in 20 % glycerol was solubilized in 1/3 Miller’s modified Luria broth (LB) medium and 10 μL of suspension was dripped in the middle of a sterile cover glass and immediately treated by the plasma. Ten μL of E. coli BW25113 overnight culture was also placed in the