Photoswitchable semiconducting polymer dots with photosensitizer molecule and photochromic molecule loading for photodynamic cancer therapy

Photodynamic therapy (PDT) is a new and rapidly developing treatment modality for clinical cancer therapy. Semiconductor polymer dots (Pdots) doped with photosensitizers have been successfully applied to PDT, and have made progress in the field of tumor therapy. However, the problems of severe photosensitivity and limited tissue penetration depth are needed to be solved during the implementation process of PDT. Here we developed the Pdots doped with photosensitizer molecule Chlorin e6 (Ce6) and photochromic molecule 1,2-bis(2,4-dimethyl-5-phenyl-3-thiophene)-3,3,4,5-hexafluoro-1-cyclopentene (BTE) to construct a photoswitchable nanoplatform for PDT. The Ce6-BTE-doped Pdots were in the green region, and the tissue penetration depth was increased compared with most Pdots in the blue region. The reversible conversion of BTE under different light irradiation was utilized to regulate the photodynamic effect and solve the problem of photosensitivity. The prepared Ce6-BTE-doped Pdots had small size, excellent optical property, efficient ROS generation and good photoswitchable ability. The cellular uptake, cytotoxicity, and photodynamic effect of the Pdots were detected in human colon tumor cells. The experiments in vitro indicated that Ce6-BTE-doped Pdots could exert excellent photodynamic effect in ON state and reduce photosensitivity in OFF state. These results demonstrated that this nanoplatform holds the potential to be used in clinical PDT.