Ratiometric near-infrared fluorescence nanothermometry in the OTN-NIR (NIR II/III) biological window based on rare-earth doped β-NaYF4 nanoparticlesElectronic supplementary information (ESI) available: OTN-NIR fluorescence temperature measurement under physiological conditions. See DOI: 10.1039/c7tb00070g

A novel nanothermometer based on over-1000 nm (OTN) near-infrared (NIR) emission of rare-earth doped ceramic nanophosphors (RED-CNPs) was developed for temperature measurement in deep tissue. Hexagonal-phase β-NaYF 4 nanoparticles co-doped with Yb 3+ , Ho 3+ , and Er 3+ (NaYF 4 :Yb 3+ ,Ho 3+ ,Er 3+ NPs) were synthesized and used as a nanothermometer. The NaYF 4 :Yb 3+ ,Ho 3+ ,Er 3+ NPs displayed two OTN-NIR emission peaks in the second (NIR-II) (at 1150 nm of Ho 3+ ) and third (NIR-III) (at 1550 nm of Er 3+ ) biological window regions under NIR (980 nm) excitation in the first (NIR-I) biological window region. Oleic acid (OA) capped NaYF 4 :Yb 3+ ,Ho 3+ ,Er 3+ NPs were dispersed in non-polar media, i.e. , cyclohexane, and showed a temperature-dependent intensity ratio of the emission peaks of Ho 3+ and Er 3+ ( I Ho / I Er ). The temperature-dependent I Ho / I Er of the OA-NaYF 4 :Yb 3+ ,Ho 3+ ,Er 3+ NPs was also evident through imitation tissue. The surfaces of the NaYF 4 :Yb 3+ ,Ho 3+ ,Er 3+ NPs were modified with a poly(ethylene glycol) (PEG)-based block copolymer. The PEGylated NaYF 4 :Yb 3+ ,Ho 3+ ,Er 3+ NPs were dispersed in water and emitted strong NIR-II and III emissions under NIR-I excitation. The PEGylated NaYF 4 :Yb 3+ ,Ho 3+ ,Er 3+ NPs were injected into mice via the tail vein, and the OTN-NIR emissions of the PEGylated NaYF 4 :Yb 3+ ,Ho 3+ ,Er 3+ NPs from the mouse blood vessels were clearly observed using an OTN-NIR fluorescence in vivo imaging system. In a polar media, water, the I Ho / I Er of PEGylated NaYF 4 :Yb 3+ ,Ho 3+ ,Er 3+ NPs was inversely related to the temperature. In both non-polar and polar media, the I Ho / I Er values of the NaYF 4 :Yb 3+ ,Ho 3+ ,Er 3+ NPs were almost linearly dependent on the temperature. The obtained NaYF 4 :Yb 3+ ,Ho 3+ ,Er 3+ NPs are promising as a novel fluorescent nanothermometer for deep tissue. A novel ratiometric nanothermometer based on over-1000 nm near-infrared emission of rare-earth doped ceramic nanophosphors was developed for temperature measurement.