Cold Atmospheric Pressure Plasma Array for Biofilm Inactivation

Abstract

Cold atmospheric pressure (CAP) plasma has been shown to kill bacteria and remove biofilms. This could be useful in the food processing industry where microbial contamination of food contact surfaces are a source of foodborne illness. Single linear plasma discharge devices lack the spatial coverage that an array of discharges offers, and common plasma jet arrays require dithering or other means of movement to cover the same area. Our group has developed a CAP array assembled from multiple linear discharges that can be used to inactivate bacterial biofilms over large treatment areas. Each linear discharge consists of 2 opposing metal electrodes ($24\ \text{mm}\times 1\ \text{mm}$) buried below $125\ \mu\mathrm{m}$ of Low Temperature Co-fired Ceramic (LTCC). The gap between electrodes is $750\ \mu\mathrm{m}$. These devices operate with an AC voltage (0.5-2 kV), an Argon gas flow (3–13 LPM), and a typical discharge current from a single element of 1–2 mA. To form arrays of discharge elements, stacks of linear discharge elements containing two opposing embedded electrodes are assembled. To ensure uniformity of the discharge elements, we have tested external ballast resistances of 1, 100, 200 $\mathrm{k}\Omega$, and demonstrated the importance of resistances between 100 $\mathrm{k}\Omega$ and 200 $\mathrm{k}\Omega$ on discharge uniformity. In a different configuration, internal ballast resistors are used. The HV AC electrodes can then share a common electrical connection so that only 2 wires are needed to drive the array elements in parallel. Internal ballast resistors, fabricated using a DuPont thick film resistor paste, are used to create $\approx 150\ \mathrm{k}\Omega$ resistors on the ground side of each discharge element embedded within the LTCC substrate. An 8 element discharge array has been demonstrated with an area of $29\ \text{mm}\times 15\ \text{mm}$. The devices are designed for modularity when adding additional discharge elements. We demonstrate the effectiveness of these devices in inactivating common foodborne pathogens and spoilage organisms (E. coli, Pseudomonas, etc) in biofilms formed on steel, glass, and plastic substrates. We see a dramatic reduction in viable Colony Forming Units of >90% with short plasma treatment. These results will be presented.