Er3+ Sensitized 1530 nm to 1180 nm Second Near‐Infrared Window Upconversion Nanocrystals for In Vivo Biosensing

Fluorescent bioimaging in the second near-infrared window (NIR-II) can probe deep tissue with minimum auto-fluorescence and tissue scattering. However, current NIR-II fluorophore-related biodetection in vivo is only focused on direct disease lesion or organ bioimaging, it is still a challenge to realize NIR-II real-time dynamic biosensing. A new type of Er³⁺ sensitized upconversion nanoparticles are presented with both excitation (1530 nm) and emission (1180 nm) located in the NIR-II window for in vivo biosensing. The microneedle patch sensor for in vivo inflammation dynamic detection is developed based on the ratiometric fluorescence by combining the effective NIR-II upconversion emission and H₂ O₂ sensing organic probes under the Fenton catalysis of Fe²⁺ . Owing to the large anti-Stokes shifting, low auto-fluorescence, and tissue scattering of the NIR-II upconversion luminescence, inflammation can be dynamically evaluated in vivo at very high resolution (200×200 μm).