A Visible/NIR-II Ratiometric Fluorescent Nanoprobe for Tissue Depth Analysis.

Fluorescence imaging is a promising approach for in vivo real-time two-dimensional (2D) visualization of biological structures. However, it is still a challenging problem to acquire depth information conveniently from 2D images. Herein, we developed a visible/second near-infrared (NIR-II) ratiometric fluorescence strategy to acquire tissue depth from 2D fluorescence imaging. A ratiometric fluorescent probe TAC NSs that emitted red and NIR-II fluorescence was prepared through electrostatic interactions between poly-(ethylene-imine)-modified Ti₃C₂ MXene nanosheets and CdTe and Ag₂S quantum dots (QDs). The visible/NIR-II fluorescence ratio decreased exponentially with increasing tissue depth, and its natural logarithm (ln) values shows good linear relationship with tissue depth in the range of 0–1.0 mm and 1–2.5 mm, respectively. Notably, the ratiometric fluorescence at a fixed tissue depth is not affected by the concentration of TAC NSs, indicating that the tissue depth analysis is not interfered by the nonuniform tissue distribution of TAC NSs. Moreover, the TAC NSs exhibited efficient photothermal conversion ability for tumor ablation. This work can provide a strategy for acquiring three-dimensional information from in vivo fluorescence imaging. [ABSTRACT FROM AUTHOR]