ROS generated by photo-excited carotenoids attacks tumor cells

A possibility of carotenoids as a photosensitizer in photodynamic therapy (PDT) was explored using fluorescence imaging.Singlet oxygen (1O2), one of the reactive oxygen species (ROS), is known to have toxicity to cells. Green plants use several carotenoids, which have n>10 length of the conjugated double bond, to relax 1O2 involuntarily generated by photosynthetic process. Some carotenoids have the T1 level (first triplet excited level) just below the energy level of 1O2 and can plunder energy from 1O2 by energy transfer and change the energy to heat by intersystem crossing. Conversely, some carotenoids with n