Sonodynamic therapy (SDT), a new approach to the treatment of cancer, is based on synergistic cell killing through a combination of sonosensitization and ultrasound, although the mechanism responsible for the effect remains to be elucidated. We have been interested in the emission of light due to acoustic cavitation induced by ultrasound irradiation, defined as sonoluminescence, and have been studying SDT for its potential application to secondary photodynamic therapy (PDT) . We carried out a quantitative study to determine the waveforms and peak wavelengths of luminescence in an aqueous solution subjected to ultrasonic excitation and also those of light obtained through ultrasound exposure by adding a photosensitizer to the solution. We then compared the resulting spectrograms with respect to the absorption wavelength and fluorescence wavelength of the drug. We confirmed that the fluorescence wavelength spectra obtained by ultrasound excitation of aqueous solutions of photosensitizers were formed due to absorption of some of the sonoluminescence and additional drug-specific fluorescence. We also found that the specific excitation spectrum of each photosensitizer was considerably decreased when DABCO, a singlet oxygen scavenger, was added to this experimental system.
