NIR-II Responsive Upconversion Nanoprobe with Simultaneously Enhanced Single-Band Red Luminescence and Phase/Size Control for Bioimaging and Photodynamic Therapy.

Lanthanide based upconversion (UC) nanoprobes are emerged as promising agents for biological applications. And, extending the excitation light to the second near-infrared (NIR-II) instead of the traditional 980/808 nm light and realizing NIR-II responsive single band red UC emission is highly demanded for bioimaging application, which has not yet been explored. Here, a new type of NIR-II (1532 nm) light responsive UC nanoparticles (UCNPs) with enhanced single band red UC emission and controllable phase and size is designed by introducing Er 3+ as sensitizer and utilizing Mn 2+ as energy manipulator. Through tuning the content of Mn 2+ in NaLnF 4 :Er/Mn, the crystal phase, size and emitting color are readily controlled, and the red-to-green (R/G) ratio is significantly increased from ∼25 to ∼300, leading to NIR-II responsive single band red emission via efficient energy transfer between Er 3+ and Mn 2+ . In addition, the single band red emitting intensity can be further improved by shell coating to avoid the surface quenching effect. More importantly, NIR-II light activated red UC bioimaging and NIR-II light responsive photodynamic therapy (PDT) through loading photosensitizer of zinc phthalocyanine (ZnPc) were successfully achieved for the first time. These findings provide a new strategy of designing NIR-II light responsive single band red emissive UCNPs for biomedical applications. This article is protected by copyright. All rights reserved.