Sterilization efficacy of dielectric barrier discharge on non-uniform surfaces

Abstract

In this study we investigate effectiveness of the dielectric barrier discharge (DBD) excited by nanosecond rise and fall time voltage pulses to kill bacteria located within indentations on surfaces. The nanosecond pulsed DBD produces uniform plasma independently of the uniformity of the bacteria covered surface acting as one of the DBD electrodes. The experimental set-up consists of a flat high voltage electrode insulated by a thin layer of quartz. Bacteria ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Escherichia</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">coli</i> ) are plated onto the surface of agar at concentrations of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> colony forming units (CFUs). Agar plates were prepared specially having non-uniform surfaces (with ridges and indentations) to mimic the real case for living skin tissue. We compared the sterilization effectiveness of nanosecond and conventional DBD by applying nanosecond pulses and microsecond long pulses produced at same rates with same equivalent power. We observed visually that the nanosecond DBD produced uniform plasma, while the conventional DBD produced micro-discharges that were often terminated on the top of the ridges. Sterilization results were evaluated by culturing the bacteria. Preliminary results indicate that nanosecond DBD can sterilize non-uniform surfaces significantly faster than the conventional DBD does.