Abstract
Recent studies show the feasibility of photodynamic inactivation of green algae as a vital step towards an effective photodynamic suppression of biofilms by using functionalized surfaces. The investigation of the intrinsic mechanisms of photodynamic inactivation in green algae represents the next step in order to determine optimization parameters. The observation of singlet oxygen luminescence kinetics proved to be a very effective approach towards understanding mechanisms on a cellular level. In this study, the first two-dimensional measurement of singlet oxygen kinetics in phototrophic microorganisms on surfaces during photodynamic inactivation is presented. We established a system of reproducible algae samples on surfaces, incubated with two different cationic, antimicrobial potent photosensitizers. Fluorescence microscopy images indicate that one photosensitizer localizes inside the green algae while the other accumulates along the outer algae cell wall. A newly developed setup allows for the measurement of singlet oxygen luminescence on the green algae sample surfaces over several days. The kinetics of the singlet oxygen luminescence of both photosensitizers show different developments and a distinct change over time, corresponding with the differences in their localization as well as their photosensitization potential. While the complexity of the signal reveals a challenge for the future, this study incontrovertibly marks a crucial, inevitable step in the investigation of photodynamic inactivation of biofilms: it shows the feasibility of using the singlet oxygen luminescence kinetics to investigate photodynamic effects on surfaces and thus opens a field for numerous investigations.
Highlights
Biofilms play a major role in biofouling and the biodeterioration of construction materials.The biodeterioration of a building compromises its aesthetic appearance, but can destroy cultural heritage when it comes to ancient buildings and even endanger people when the structural integrity is affected [1,2,3,4]
In contrast to titanium dioxide, which absorbs in the UV, surfaces functionalized with photosensitizers would use a much larger part of the Sun’s emission spectrum reaching our planet
For advancing the photodynamic inactivation (PDI) of phototrophic microorganisms beyond a mere proof of concept, we considered that the step should be to evaluate the utilization of direct singlet oxygen (1 O2 )
Summary
Biofilms play a major role in biofouling and the biodeterioration of construction materials. In contrast to titanium dioxide, which absorbs in the UV, surfaces functionalized with photosensitizers would use a much larger part of the Sun’s emission spectrum reaching our planet. Another advantage of photosensitizers is their low to non-existing dark toxicity, having been developed for medical use in most cases. While the photosensitizer s fluorescence may be analysed for deducing on its location and possible aggregation, the analysis of the 1 O2 luminescence kinetics provides an insight on the microenvironment of the photosensitizer This may be used for revealing the biochemical mechanism of the inactivation, allowing for optimization of the photosensitizer in terms of localisation and effective singlet oxygen generation [26,27]
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