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.