Photosensitizers for Two-Photon Excited Photodynamic Therapy

Photodynamic therapy (PDT) is a noninvasive protocol for the treatment of various cancers and nonmalignant diseases. Light, oxygen, and photosensitizer (PS) are the essential three elements in a typical PDT process. Currently, there are two major barriers limiting the further development of PDT. One issue is limited tissue penetration, and the other is the lack of high-performance PSs. Therefore, the newly emerging two-photon excited PDT (2PE-PDT) has attracted considerable attention in recent years due to its advantages such as a higher spatial resolution and a greater penetration depth. In this review, focus is on (i) the principle of 2PE-PDT, (ii) the progression of PSs for 2PE-PDT, and (iii) the potential indications and future directions in this field.