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Optica Publishing Group
  • International Quantum Electronics Conference
  • OSA Technical Digest (Optica Publishing Group, 1984),
  • paper FB4

Two-Step Laser Photobiology: Application for Cancer Treatment

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Abstract

A new method of laser photobiology and photochemotherapy is considered. It consists in producing, by two-step laser excitation, an irreversible modification in a chromophore attached to a given biomolecule. The excitation may lead to the ionization, the dissociation, or other irreversible chemical modifications of the chromophore. The resulting photoproducts may then induce a chemical change on the biomolecule. This phenomenon is contrasted with the photodynamic action, where the chemical change in the biomolecule is produced by the surrounding oxygen molecules raised to the first excited singlet state by energy transfer from the excited chromophore. The possible advantages of this two-step photosensitization process over photodynamic action may be as follows: (a) The two-step process appears to be of rather general validity, while the photodynamic action requires chromophores with high quantum yields for both the production of the chromophore triplet state and for the energy transfer to the oxygen. One may further notice that, for the photodynamic action, oxygen needs to be readily available to the chromophore. (b) On account of the different products that are involved, the chemical pathways of the two processes are expected to be generally different, and this may lead to new and interesting effects. In particular, oxygen may not be necessarily involved in the two-step processes, and this can be advantageous in dealing with systems with low oxygen concentration. (c) If the wavelengths of the two exciting waves are appropriately chosen, the two-step process may result in a selective action on the given chromophore. (d) The selectivity may be further increased by using pulsed beams for the two waves and by sending the two exciting pulses delayed by an appropriate amount.

© 1984 Optical Society of America

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