The present study investiaged the enhancement of nonlinear optical properties of Protoporphyrin IX in photodynamic therapy using nano-droplet. To this end; absorbance, fluorescence, and nonlinear optical properties of Protoporphyrin IX were examined and results showed that dye aggregation and dielectric constant of solvent could change absorbance and fluorescence spectra. According to quantum mechanical perturbation theory, dipole moment of Protoporphyrin IX in solutions of water-ethanol was extracted. The values of nonlinear absorption and nonlinear refractive index of Protoporphyrin IX in AOT/Toluene/H2O were also reproted to be larger than aqueous solutions, due to polarity reduction of solvent as well as discount of Protoporphyrin IX aggregation in AOT/Toluene/H2O. Furthermore, the effect of cell culture media on the nonlinear optical properties of Protoporphyrin IX was analyzed and the results were compared with those of water. The photon correlation spectroscopy of solution also showed a growth in dye-droplet aggregation following the increase of Protoporphyrin IX concentration.

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