Generation of Singlet Oxygen by Persistent Luminescent Nanoparticle–Photosensitizer Conjugates: A Proof of Principle for Photodynamic Therapy without Light

Broader application of photodynamic therapy of cancer as a treatment protocol is hampered by the limited penetration of light through the mammalian tissues. Since the photosensitized generation of cytotoxic singlet oxygen requires effective excitation of the tumor-localized photosensitizer, photodynamic action can only be guaranteed for the first few millimeters of the irradiated tissues. In this work, we demonstrated that the phenomenon of persistent luminescence which is delayed emission from certain metal ion excited states, while crystal defects acting as energy traps, can provide an alternative excitation possibility. Thus, persistent luminescent nanoparticles functionalized by FRET-matching Bodipy sensitizers, can be excited in situ, before administration into a cell culture or an organism, and keep on producing singlet oxygen regardless of their location, without any need for continuous photonic excitation.