Advancing neodymium single-band nanothermometry.

Near-infrared (NIR) emitting contrast agents with integrated optical temperature sensing are highly desirable for a variety of biomedical applications, particularly when subcutaneous target visualization and measurement of its thermodynamic properties are required. To that end, the possibility of using Nd doped LiLuF rare-earth nanoparticles (RENPs) as NIR photoluminescent nanothermometers is explored. These RENPs are relatively small, have narrow size distribution, and can easily be core/shell engineered - all combined, these features meet the requirements of biologically relevant and multifunctional nanoprobes. The LiLuF host allows to observe the fine Stark structure of the F→I, I, and I optical transitions, each of which can then be used for single-band NIR nanothermometry. The thermometric parameter defined for the most intense Nd emission around 1050 nm, shows high temperature sensitivity (∼0.49% °C), and low temperature uncertainty (0.3 °C) as compared to the thermometric parameters defined for the 880 and 1320 nm Nd emissions. Additionally, transient temperature measurements through tissue show that these RENPs can be used to assess fast temperature changes at a tissue depth of 3 mm, while slower temperature changes can be measured at even greater depths. Nd doped LiLuF RENPs represent a significant improvement for Nd based single-band photoluminescence nanothermometry, with the possibility of its integration within more sophisticated multifunctional theranostic nanostructures.