Decoupled Rare-Earth Nanoparticles for On-Demand Upconversion Photodynamic Therapy and High-Contrast Near Infrared Imaging in NIR IIb

Rare-earth doped multi-shell nanoparticles slated for theranostic applications produce a variety of emission bands upon near-infrared (NIR) excitation. Their downshifting emission is useful for high-contrast NIR imaging, while the upconversion light can induce photodynamic therapy (PDT). Unfortunately, integration of imaging and therapy is challenging. These modalities are better to be controlled independently so that, with the help of imaging, selective delivery of a theranostic agent at the site of interest could be ensured prior to on-demand PDT initiation. We introduce here multi-shell rareearth doped nanoparticles (RENPs) arranged in a manner to produce only downshifting emission for NIR imaging when excited at one NIR wavelength and upconversion emission for therapeutic action by using a different excitation wavelength. In this work, multi-shell RENPs with a surface-bound sensitizer have been synthesized for decoupled 1550 nm downshifting emission upon 800 nm excitation and 550 nm upconversion emission caused by 980 nm irradiation. The independently controlled emission bands allow for high-contrast NIR imaging in NIR-IIb of optical transparency that gives highcontrast images due to significantly reduced light scattering. This can be conducted prior to PDT using 980 nm to produce upconverted light at 550 nm that excites the RENP surface-bound photosensitizer, Rose Bengal (RB), to effect photodynamic therapy with high specificity and safer theranostics.