Photodynamic Action in Thin Sensitized Layers: Estimating the Utilization of Light Energy

The result of photodynamic action significantly depends on the density of the light dose absorbed by the photosensitizer. The efficiency of using light to excite photosensitizer molecules and minimization of its loss plays an important role in ensuring the overall success of the process. When carrying out photodynamic treatment of thin sensitized layers (such as inactivation of surface pathogens or in vitro screening studies of photosensitizers), only a part of the light dose is absorbed in the layer, while a significant part is lost, especially at low concentrations of the photosensitizer. In this work, we evaluate the decrease in absorbed light dose depending on the extinction and concentration of the photosensitizer in a thin sensitized layer, the shape of its absorption spectrum, and the shape of the excitation light source spectrum. It was found out that a significant loss of the absorbed dose occurs upon excitation of photosensitizers, especially with low extinction, when using light sources with a broad emission spectrum. This loss must be taken into consideration when predicting the results of photodynamic exposure and optimizing its tactics.