Self-monitored biological nanoheaters operating in the first biological window based on single-band red upconversion nanoparticles fabricated through architectural design

Achieving controllable heating in deep tissue is of vital importance for photothermal therapies. In this work, we developed single-band red upconversion (UC) nanoparticles (NPs) as self-monitored photothermal probes. The excitation (∼800 nm) and emission (∼652 nm) of the developed UCNPs are both located in the first biological window (I-BW), reducing the optical energy dissipation caused by biological tissue. The emission spectroscopic characteristics of these UCNPs were investigated, as well as their corresponding UC mechanisms. Moreover, the light-to-heat efficiency of the UCNPs reached 40%, and the self-monitored temperature feedback was demonstrated using the highly efficient red emission. The proposed UCNPs can deepen the penetration and avoid overheating in biological tissues if used in photothermal therapies. We consider that these characteristics will favour their use as in vivo photothermal probes with feedback provided by their emission of light.