Highly Efficient Two-Photon Photodynamic Therapy Using Light-Sheet Excitation

Two-photon photodynamic therapy (TP-PDT), which utilizes near-infrared light to excite photosensitizer via two-photon excitation (TPE), is a promising modality in the treatment of deeply seated tumors or thick tumors. However, the TPE domain is much smaller than the tumor volume, significantly limiting the therapeutical outcomes of TP-PDT. Here, a light-sheet TPE system is designed and constructed using a cylindrical lens for highly efficient TP-PDT. The light-sheet TPE performance is characterized and optimized via theoretical analysis and experimental studies in solution, phantom, and tumor. The optimized excitation system can reach a large TPE domain of 2.6 × 2.7 × 0.09 mm in the tumor, which is not achievable using conventional TPE methods, enabling TPE and subsequently generated reactive oxygen species to cover the whole tumor under line-scanning. Outstanding TP-PDT therapeutic performance of 70% tumor growth inhibition rate is achieved under line-scanned light-sheet TPE, making the proposed light-sheet excited TP-PDT a potential therapeutic tool for future translational research.