Ultra-sensitive optical nano-thermometer LaPO4: Yb3+/Nd3+ based on thermo-enhanced NIR-to-NIR emissions

Accurate deep-tissue thermometry integrated with bio-imaging and self-heating functions is urgently desired for effective photo-thermal therapy (PTT) with minimized collateral damages. Herein, urchin-like LaPO4: Yb3+/Nd3+ nano-thermometers working in the biological window region were developed with ultra-high sensitivity and sub-degree resolution. Unique thermal enhancement of near-infrared (NIR) emissions (F-4(3/2) -> I-4(9/2)) over 1000 times was detected, which was systematically investigated based on phonon-assisted energy transfer process. Irradiated by 980 nm laser, the self-heating effects of urchin-like samples were analyzed, while NIR thermal sensing behaviors were evaluated using ladder-like F-4(7/2)-F-4(5/2)-F-4(3/2) states as thermal coupled levels (TCLs). The penetration depth of NIR emissions was determined through spectral measurement at varied tissue thickness, and ex vivo experiments were rationally designed to assess the self-heating and thermal reading features of samples in deep-tissues. These findings reveal the great superiority of the present thermo-enhanced NIR-to-NIR nanoprobes for bio-imaging and thermometry in deep-tissues, which opens a promising pathway for self-monitored PTT.