1 Introduction of PDT
PDT is an emerging non-invasive cancer treatment(Kwiatkowski et al.
2018) that uses photosensitizers, light and endogenous molecular oxygen
to kill cancer cells or microorganisms(Dougherty et al. 1998). Hermann
von Tappeiner first proposed the ”photodynamic effect”, reporting that
certain dyes can make microorganisms sensitive to light and that
exposure to sunlight can rapidly lead to cell death(Kessel 2019).
Photosensitizer is not toxic to cells before illumination.
Photosensitizer forms an excited singlet state when irradiated by light
at appropriate energy wavelengths and then transforms into a long-lived
excited triplet state; this triplet state can undergo photochemical
reactions in the presence of oxygen, transferring energy to surrounding
oxygen molecules and forming reactive oxygen species (ROS), which kill
cancer cells, pathogenic microorganisms and unwanted tissues(Abrahamse
and Hamblin 2016; Castano et al. 2004; Josefsen and Boyle 2008; Nyman
and Hynninen 2004; Weizman et al. 2000). How photosensitizers under
light conditions transfer energy to oxygen molecules? And how to improve
the light energy capture efficiency of photosensitizers are questions to
be further explored by scientists.