The composite system can be prepared by
incorporation of methylene blue (MB) into the channels of
zeolite and by adsorption on the surface of the crystals. The
composite photosensitizer effectively absorbs the red light
(λ
max = 648 nm) and upon illumination with light-emitting
diode at a fluence rate of 1.02 mW cm
-2 generates
effectively reactive singlet oxygen in aqueous solution,
which was proved by EPR spectroscopy. To test efficiency
for inactivation of pathogenic microorganisms, we measured
photokilling of bacteria
Escherichia coli
and
Staphylococcus
aureus
and yeasts
Candida albicans
. We found
out that after the microorganisms have been adsorbed at the
surface of such modified zeolite, the photogenerated singlet
oxygen quickly penetrates their cell walls, bringing about
their effective photoinactivation. The growth inhibition
reached almost 50 % at 200 and 400 mg modified zeolite
in 1 ml of medium in
E. coli and
C. albicans, respectively.
On the other hand, the growth inhibition of
S. aureus
reached 50 % at far smaller amount of photocatalyst
(30 μg per 1 ml of medium). These results demonstrate
differences in sensitivities of bacteria and yeast growth.
The comparison revealed that concentration required for
IC
50 was in case of
C. albicans several orders of magnitude
lower for a zeolite-immobilized dye than it was for a freely
dissolved dye. In
S. aureus, this concentration was even
lower by four orders of magnitude. Thus, our work suggested
a new possibility to exploitation of zeolite and MB
in the protection of biologically contaminated environment,
and in photodynamic therapy.
