Surface micro-discharge (SMD)

There is an urgent need for an efficient technology of disinfection
and sterilization in view of the alarming dimensions health
care-associated infections (HAIs) have reached. Cold atmospheric
pressure plasma (CAP) can be utilized for hygienic and medical
purposes, in particular in surface decontamination applications,
and provides a promising alternative to the conventionally used
sterilization techniques. Surface Micro-Discharge (SMD) offers a
technology for generating CAP that can be applied to wide areas. In
the present work, I investigate the plasma chemistry involved in
the inactivation of microorganisms by application of the SMD in
order to optimize the antimicrobial effect. For this purpose,
different strains of vegetative bacteria and bacterial endospores
are exposed to the SMD with experimental parameters such as the gas
composition, power input, treatment duration and humidity varied.
At the same time, the concentration of ozone produced by the SMD is
monitored, and its correlation with the antimicrobial efficacy is
investigated. I demonstrate that the bactericidal effect of the SMD
on both the Gram-negative Escherichia coli and Gram-positive
Enterococcus mundtii is similar and strongly correlates with the
ozone concentration. The sporicidal effect on Geobacillus
stearothermophilus is crucially affected by the humidity, whereas
the ozone concentration appears to have no influence. In addition,
I investigate the dynamic behavior of ozone produced by the SMD by
varying the geometry and the time interval for the plasma
generation and by igniting the plasma in two subsequent phases with
different frequencies. Possible explanations for the obtained
results are provided. This work fortifies the role of SMD as an
efficient sterilization method and discloses diverse possibilities
for optimizing the antimicrobial effect.