Division of Environmental Physics -
Students Faculty of Mathematics, Physics and Informatics, Comenius University Bratislava
Zuzana KOVAĽOVÁ, born Šipoldová alumni student
PhD. study 2012 - 2016
Supervisor: Zdenko Machala Consultant: Emmanuel Odic Title: Bio-decontamination of biofilms on surfaces by cold plasma Abstract: In this PhD thesis, biomedical applications of low-temperature plasmas at atmospheric pressure are investigated. In particular, bio-decontamination of planktonic bacteria and bacterial biofilms on both flat and complex surfaces by direct current (DC) air corona discharges and by pulsed discharges in argon is considered. We first provide a theoretical overview of biofilms, plasmas, and the current state of knowledge on bio-decontamination by low temperature plasma, as well as methods presently used for biofilm decontamination in the plasma medicine domain.
We characterize three plasma sources for the decontamination of Escherichia coli bacteria and biofilm. DC corona discharges in air - positive streamer corona and negative Trichel pulses were used for decontamination of planktonic bacteria and bacterial biofilms.
In some experiments water was electrosprayed onto samples from a high voltage (HV) electrode. Stable reactive species were identified in the gas phase by Fourier transform infrared spectroscopy (FTIR) and the concentration of reactive oxygen and nitrogen species was measured
in the electrosprayed water. Bio-decontamination of bacterial biofilms was carried out on glass cover slides. Within 15 min of the plasma treatment, most of the bacteria were rendered uncultivable. Some of the uncultivable bacteria remained viable, only bacteria in the top layers of the biofilm were killed, as demonstrated by a confocal laser scanning microscopy
(CLSM) of biofilms stained by live/dead viability kit. Water electrospray through the corona discharges significantly improves the biofilm inactivation and disintegrates the polymeric protective matrix of the biofilm. The second plasma source investigated was the pulsed corona discharge propagated inside long narrow quartz tubes, in which dry argon or argon with water vapor were flowing at atmospheric pressure. This type of discharge has a potential application in decontamination of inner surfaces of catheters or other long tubular devices, and could be able to deliver
low-temperature plasma over longer distances inside the human body. This pulsed corona discharge was characterized by its electrical parameters, such as the discharge propagation velocity and the mean electric field in the plasma channel. Optical emission spectroscopy of such plasma identified UV B emission form excited hydroxyl radicals, especially with humid argon working gas. The effect of this UV B was tested on planktonic bacteria sensitive to
UV damage (recA-), and was found to cause a substantial damage even to bacteria placed far downstream in the tube or on the outer surface of the tube.
The third plasma source tested was an argon jet based on cylindrical
dielectric barrier discharge with dry, humid or water saturated argon as a working gases. This discharge was used for biofilm decontamination, where we obtained similar results as with DC corona discharges – strong inactivation of biofilm bacteria determined from the cultivability tests and biofilm thickness shrinkage shown by CLSM. We used this discharge to test the effect
of vacuum UV on bacterial survival, but the effect was neither confirmed nor disproved.
MSc. study 2010 - 2012
Supervisor: Zdenko Machala Consultant: -- Title: Bio-decontamination of teeth and plastic surfaces by cold plasma of corona discharge Abstract: The bio-decontamination of Streptococci biolm on teeth
and plastic surfaces is the main interest of this work. For this
purpose, we used cold plasma of two corona discharges: positive
streamer corona and negative Trichel pulses. We show
that decontamination by these atmospheric pressure air DC
discharges is a new ecient method for biolm elimination
from teeth and plastic surfaces. We also tested positive transient
spark, though it was not suitable for expositions longer
than 2 minutes. Corona reduced bacterial population (evaluated
by log10) on contaminated teeth by 2.73 orders of
magnitude in 10 min exposure time in average.
The same discharges were also tested with the electrospraying
of water through a hollow needle - high voltage
electrode. Enhancement of plasma biocidal eects by water
spraying was investigated. Our results display that reduction
of bacterial population without water spraying on plastic
and teeth were similar - around 1 log (e.g. 90%). Water
spraying increased the bacterial reduction up to 4 logs with
both types of samples.
An analysis of tooth surfaces after plasma treatment was
made by visualisation of treatment surface with a scanning
electron microscope (SEM) and spectroscopic analysis with
Fourier transform infrared spectroscopy (FTIR) and energydispersive
X-ray analysis (EDX). We found small changes in
the morphology and the sample composition caused by exposition
to plasma for 10 min on SEM images and EDX
spectra. However, these results are not nal and require further
Bc. study 2009 - 2010
Supervisor: Zdenko Machala Consultant: -- Title: Bio-decontamination of surfaces from bacterial spores in electric discharges Abstract: