Two-photon excitation studies of m-THPC photosensitizer and photodynamic activity in an epithelial cell line.

A femtosecond laser delivering pulses of wavelength 800nm and 124fs duration at rates of 1kHz has been used to investigate the two-photon excited fluorescence in the photosensitizer m-THPC. The scaling of fluorescence amplitude with laser power and fluorescence sidelight imaging are found to support a predominantly two-photon excitation mechanism. A value for the two-photon cross-section of δ=1.8×10(-57)m(4)s is derived by comparing the fluorescence signals excited by wavelengths of 800 and 400nm. Preliminary results demonstrating the two-photon induced PDT activity of m-THPC in an epithelial cell line are also reported.