Two-photon photodynamic therapy

We demonstrate the use of infrared excitation in conjunction with an efficient two-photon absorbing dye and a photosensitizer in photodynamic therapy. An efficient two-photon absorbing dye is excited by short infrared (800 nm) laser pulses, which transfer its energy to the photosensitizer and the photosensitizer, in turn, generates the singlet oxygen. A new approach to photodynamic cancer therapy based on the strong two-photon absorption of certain newly developed organic molecules. Near infrared pulsed laser light efficiently excites these molecules which, in turn, transfer the energy to the photosensitizer used in photodynamic therapy. A newly synthesized two-photon absorbing dye 4-[N-(2-hydroxyethyl)-N-(methyl) amino phenyl]-4′-(6-hydroxyhexyl sulfonyl)stilbene (APSS), which exhibits a strong two-photon absorption at 800 nm, and upconverted fluorescence at 520 nm, in solution in the presence of a photosensitizer was found to generate singlet oxygen under infrared excitation (800 nm). The generation of singlet oxygen in a reaction system containing two-photon absorbing dye and photosensitizer under infrared excitation has been chemically detected by using ADPA (9,10-anthracenedipropionic acid) as singlet oxygen detector. The efficient two-photon absorption of certain chromophores can be used to extend photodynamic therapy to the near infrared spectral region. Whereas the photosensitizer itself may not exhibit two-photon absorption, it could be used in conjunction with one of these new chromophores. The chromophores can act as `photon harvesters' whereby they absorb two photons of near infrared light and transfer the energy to the photosensitizer, which can generate singlet oxygen in the presence of atmospheric oxygen.