Near-infrared light induced in vivo photodynamic therapy of cancer based on upconversion nanoparticles

Upconversion nanoparticles (UCNPs) that emit high-energy photons upon excitation by the low-energy near-infrared (NIR) light are emerging as new optical nano-probes useful in biomedicine. Herein, we load Chlorin e6 (Ce6), a photosensitizer, on polymer-coated UCNPs, forming a UCNP-Ce6 supramolecular complex that produces singlet oxygen to kill cancer cells under NIR light. Excellent photodynamic therapy (PDT) efficacy is achieved in tumor-bearing mice upon intratumoral injection of UCNP-Ce6 and the followed NIR light exposure. It is further uncovered that UCNPs after PDT treatment are gradually cleared out from mouse organs, without rendering appreciable toxicity to the treated animals. Moreover, we demonstrate that the NIR-induced PDT based on UCNP-Ce6 exhibits a remarkably increased tissue penetration depth compared to the traditional PDT using visible excitation light, offering significantly improved treatment efficacy for tumors blocked by thick biological tissues. Our work demonstrates NIR light-induced in vivo PDT treatment of cancer in animals, and highlights the promise of UCNPs for multifunctional in vivo cancer treatment and imaging.