Effects of pulse width and repetition rate of pulsed laser on kinetics and production of singlet oxygen luminescence

Pulsed and continuous-wave (CW) lasers have been widely used as the light sources for photodynamic therapy (PDT) treatment. Singlet oxygen (^1O2) is known to be a major cytotoxic agent in type-II PDT and can be directly detected by its near-infrared luminescence at 1270nm. As compared to CW laser excitation, the effects of pulse width and repetition rate of pulsed laser on the kinetics and production of ^1O2 luminescence were quantitatively studied during photosensitization of Rose Bengal. Significant difference in kinetics of ^1O2 luminescence was found under the excitation with various pulse widths of nanosecond, microsecond and CW irradiation with power of 20mW. The peak intensity and duration of ^1O2 production varied with the pulse widths for pulsed laser excitation, while the ^1O2 was generated continuously and its production reached a steady state with CW excitation. However, no significant difference (P>0.05) in integral ^1O2 production was observed. The results suggest that the PDT efficacy using pulsed laser may be identical to the CW laser with the same wavelength and the same average fluence rate below a threshold in solution.