Photosensitization tissue model.

Photosensitization in a light scattering matrix was investigated with a tissue model consisting of polystyrene microsphere scattering particles, in the presence of a Photofrin II as a photosensitizing agent, and subtilisin Carlsberg as an enzyme target. The photodynamic rate constant for irradiation at 435 nm, 545 nm, and red light was measured at different microsphere concentrations. The reaction rate was almost independent of the microspheres, ruling out a significant effect of light scattering on the integrated photosensitization efficiency. Modeling with the one-dimensional diffusion approximation showed that increasing scatterer concentrations led to lower transmission and higher diffuse reflection, such that the fractional absorption was almost constant. The quantum efficiency of enzyme inactivation in the light-scattering systems was 0.0014 +/- 0.0003. In terms of incident dose, red and green light had approximately the same effectiveness and blue light was two-fold more efficient.