Lanthanide-based Nanocomposites for Photothermal Therapy under Near Infrared Laser: Relationship between Light and Heat, Bio-stability and Reaction Temperature.

In this research, typical organic/inorganic photothermal therapy (PTT) agents were designed with combination of up-conversion luminescent (UCL) or NIR II imaging rare earth nanomaterials for photoacoustic (PA)/UCL/NIR II imaging-guided PTT under NIR laser irradiation. The results show that: (1) PTT effect mainly comes from NIR absorption and partly from the UCL light conversion. (2) The visible UCL emission is mainly quenched by the NIR absorption of the coated PTT agent and partly quenched by the visible absorption, indicating the excitation may play a more important role than in the UCL emission process. (3) The bio-stability of the composite might be decided by the synthesized reaction temperature. Among the five inorganic/organic nanocomposite, UCNP@MnO2 is the most suitable candidate for cancer diagnosis and treatment due to its stimuli-response ability to the micro-acid environment of tumor cells and highest bio-stability. The composites generate heat for PTT after entering the tumour cells, and then the visible light emission gradually regains as MnO2 is reduced to colorless Mn2+ ions, thereby illuminating the cancer cells after the therapy.