Bright Tm3+-based downshifting luminescence nanoprobe operating around 1800 nm for NIR-IIb and c bioimaging

Fluorescence imaging in the near-infrared region yields high-quality images that overcome the current depth limitations. Here, the authors report a Tm3 + -based nanoprobe for NIR-IIb/c imaging, providing references to future bioimaging beyond 1700 nm. Fluorescence bioimaging based on rare-earth-doped nanocrystals (RENCs) in the shortwave infrared (SWIR, 1000-3000 nm) region has aroused intense interest due to deeper penetration depth and clarity. However, their downshifting emission rarely shows sufficient brightness beyond 1600 nm, especially in NIR-IIc. Here, we present a class of thulium (Tm) self-sensitized RENC fluorescence probes that exhibit bright downshifting luminescence at 1600-2100 nm (NIR-IIb/c) for in vivo bioimaging. An inert shell coating minimizes surface quenching and combines strong cross-relaxation, allowing LiTmF4@LiYF4 NPs to emit these intense downshifting emissions by absorbing NIR photons at 800 nm (large Stokes shift similar to 1000 nm with a absolute quantum yield of similar to 14.16%) or 1208 nm (NIR-IIin and NIR-IIout). Furthermore, doping with Er3+ for energy trapping achieves four-wavelength NIR irradiation and bright NIR-IIb/c emission. Our results show that Tm-based NPs, as NIR-IIb/c nanoprobes with high signal-to-background ratio and clarity, open new opportunities for future applications and translation into diverse fields.

Automated summary

Fluorescence imaging in the near-infrared region is enhanced by the use of a Tm3+ -based nanoprobe for NIR-IIb/c imaging that provides references for future bioimaging above 1700nm. The study presents a type of thulium (Tm) self-sensitized rare-earth-doped nanocrystals (RENCs) fluorescence probe that emits bright downshifting luminescence at 1600-2100 nm for in vivo bioimaging. The results suggest that Tm-based NPs as NIR-IIb/c nanoprobes offer new opportunities for future applications in diverse fields.