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To determine the optimum wavelength for irradiation with coherent light after 5-ALA-induced protoporphyrin IX-sensitization, HaCaT cells were allowed to take up 5-ALA (30 (mu) g/ml) for 24 h. A tunable dye laser was used for PDT (40 mW/cm2, 30 J/cm2, wavelengths between 622 - 649 nm in steps of 3 nm). Afterwards, an MTT assay was performed to check cell viability (CV). Four groups (n equals 8) were formed: A equals controls, B equals irradiation only, C equals 5-ALA only, D equals 5-ALA and irradiation. CV of groups B, C, D were compared to those of group A (100%). Group B showed no significant difference (92% range at different wavelengths between 72% and 100%). Group D showed a significant decrease of CV (61%, range at different wavelengths between 35% and 86%). Lowest values for CV were detected at 634 and 637 nm. We believe therefore, that PDT with 5-ALA as sensitizer shows better cytotoxicity when wavelengths at 634 - 637 nm are used.
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