Modeling the Spectral Sensitivity of Singlet Oxygen Induced by Photochemical Reactions in Cells

Anti-fungal blue light (ABL) therapies are based on the photochemical reaction of endogenous photosensitizer (PS) in fungal cells. Knowing the spectral sensitivity of these cells for the ability to generate singlet oxygen is thus important to determine the most effective wavelength of such light therapies, and thereby to design ABL therapeutic devices, e.g., by light emitting diodes. We propose a modeling method of such spectral sensitivity in this work, based on the absorption spectra of cells and other inherent characteristic parameters, i.e., singlet oxygen quantum yield and the extinction coefficient of the endogenous PS. Specifically, the absorption spectra are determined by the PSs inside the fungus
Candida albicans
and human epithelial cells. Then, the concentration of PS in those two types of cells was measured by high-performance liquid chromatography (HPLC) assays. The HPLC assays show that the coproporphyrin (CP) is the main PS in
C. albicans
, accounting for 60% of the total PS. The simulation results demonstrate that the 390~420nm light can stimulate the PS in the cells to generate more singlet oxygen in
C. albicans
than in epithelial cells; and this range is the same as the CP Soret band. In contrast, the light with wavelengths >450nm is less effective in exciting the PS in
C. albicans
, and leads to more singlet oxygen generation in V.E. cells than shorter wavelength. We thus conclude that 390~420nm light is the most effective range for inhibiting
C. albicans
with the least damage to human host cells.