2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
20 digital images of randomly chosen different places ocross
the glass plate were recorded using CCD camera PixeLInK
PL-A662 mounted on the nikon microscope. At every recorded
image, the number of living cells N L (green flurescence)
and dead cells N D (orange fluorescence) was counted. Then,
the survival ratio SR was calculated:
NL
SR =
N +
L D
Results
After irradiating Candida vini suspension deposited on
the 100 R glass plate a significant inactivation was observed
– the SR dropped to 0.032 ± 0.023 within 70 minutes. On the
other hand, the non-irradiated sample showed no inactivation
within 70 minutes. These observations are in a good compliance
with the results of Seven et al. 4 , who also observed
no inactivation of microbes on titanium dioxide in darkness.
Only very small inactivation was observed on an irradiated
bare glass without the catalyst layer. (Figs. 1., 2.).
These results are in agreemnet with the observations
made by Kühna et al. 3 , who irradiated bacteria Pseudomonas
aeruginosa on a glass plate covered with titanium dioxide.
They found out that bacreial cell inactivation takes place.
This phenomenon was explained to be caused by the oxidative
stress of oxygen radicals inside cells during the exposure
by UV-A radiation. Once the stress rises over a certain
threshold, the cell dies.
Fig. 1. SR comparison for Candida vini at different conditions
on R substrates
A constant decrease of SR in a certain time from the
reaction start was observed by Benabbou et al. 2 in the case of
Escherichia coli. Cell mebrane damage resulting from photocatalytical
processes leads to an increase in membrane permaebility
and eventually to free outflow of cell fluids. Therefore
both bacterial cells as well as molecules of intracellural
organels can become the substrate of reactive oxygen species
(ROS) attack. ROS react simultaneously with the cytoplasmatic
membrane of living cells and with the remains of dead
(4)
s506
Fig. 2. SR comparison for Candida vini at different conditions
on S substrate
cells (polysycharides, lipids) at the same time. Our results
also confirm this hypothesis.
When we compare the inactivation rates for Candida vini
on R and S substrates (Fig. 2. and Fig. 1.) it becomes clear
that the inactivation rate of Candida vini does not depent on
the structure and topology of the catalyst layer, as long as the
glass surface is well couted by titanium dioxide.
Conclusions
When comparing the photocatylic inactivation rate of
Candida vini on two types of immobilised catalyst (rapidly
printed and slowly printed titanium dioxide layers) it is
possible to conclude that significant inactivation was observed
on glass plates with very high sol loading, i.e. with very
well covered surface (samples 100 R, 95 R, 95 S). We also
observe a certain decrease in the inactivation rate after reachicg
the SR value of appr. 50 %. This might be caused by the
simultaneous consuption of ROS both by the still living cells
membrane as well as the organic remains of already killed
cells. Almost constant SR value between 25 and 35 minutes
suggest a competitive reaction pathway.
Authors thank to Ministry of Education, Youth and Sports
of Czech Republic for support by project MSM0021630501.
REFEREnCES
1. Huang n., Xiao Z., Huang D., Yuan Ch.: Supramol. Sci.
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Benz V. W., Sonntag H-G., Erdinger L.: Chemosphere
53, 71 (2003).
4. Seven O., Dindar B., Aydemir S., Metin D., Ozinel M.
A., Icli S.: J. Photochem. Photobiol. Chem. 165, 103
(2004).