Difference in the effects of surfactants and albumin on the extent of deaggregation of purpurin 18, a model of hydrophobic photosensitizer.

Absorption, fluorescence and light scattering techniques have been used to monitor the deaggregation of purpurin 18, a model of hydrophobic photosensitizers for photodynamic therapy, in aqueous micelles, microemulsions and human serum albumin. The aggregates present in the neat aqueous solvents are found to undergo deaggregation in these media to different extents. Aqueous micelles and microemulsions are found to induce a complete deaggregation whereas the process is only partial in albumins. This could be an indication of the fact that such hydrophobic photosensitizers are likely to be aggregated in the blood stream, but are probably in monomeric form, upon cellular uptake. The formation of surfactant-induced aggregates at intermediate concentrations of the positively charged CTAB is also observed and is explained in the light of electrostatic interactions between the fluorophore and the surfactant.