Selection of photosensitisers for photodynamic therapy of cancer using time-resolved photothermal spectroscopy

Abstract
The photosensitisers proper for the application in photodynamic therapy have to be more efficiently introduced into cancerous than into healthy cells, non-toxic in darkness and absorb energy in the region in which cells are possibly transparent, and to destroy cancerous cell as a result of illumination. The triplet states of dyes are usually very active in photoreactions, therefore, the efficiency of triplet state generation, measured by laser induced optoacoustic spectroscopy, can be a criterion for selection of proper sensitizers. The dyes studied are introduced into model systems such as fluid solutions, films, resting (healthy) cells and stimulated cells (being models of cancerous cells). The natural pigments are usually less toxic than synthetic dyes, therefore, besides different merocyanines, also the bacteriochlorophyll c and bacteriopheophytin c have been studied by the photothermal method, absorption, fluorescence emission and fluorescence excitation spectroscopies. It has been found that the optimal sensitizer has to be chosen in a step by step selection procedure based on the investigation of a dye introduced into various (simple and complex) model systems.