Recent progress in the development of singlet oxygen carriers for enhanced photodynamic therapy

Hypoxia is a significant feature of the tumor, which has been proved to be the major challenge in translating photodynamic therapy (PDT) into clinical applications. To solve this issue, singlet oxygen carriers have been used to relieve tumor hypoxia and accordingly improve the therapeutic effect of PDT. Herein, a systematic summary of recent progress in the design and preparation of singlet oxygen carriers to overcome the hypoxia issue and realize the enhanced PDT is presented. For discussing purpose, the typical molecular backbone applied for the design and fabrication of an intelligent singlet oxygen carrier is firstly discussed, with an emphasis on the mechanism interpretation of the reversible trap and release of singlet oxygen. Furthermore, the enhanced PDT realized by innovative singlet oxygen carriers is systematically discussed in detail, including therapeutic platforms based on naphthalenes, anthracenes, and pyridines-derived small molecules or polymers. Finally, some critical points for singlet oxygen carrier design and an outlook for the future research and development of this promising field are provided. We sincerely anticipate the information presented in this review to provide insightful design guidelines for the further development of precise and efficient antitumor application systems based on the singlet oxygen carrier.