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 Nd3+ doped LiLuF4 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 LiLuF4 host allows to observe the fine Stark structure of the F-4(3/2) -> I-4(9/2), I-4(11/2), and I-4(13/2) optical transitions, each of which can then be used for single-band NIR nanothermometry. The thermometric parameter defined for the most intense Nd3+ emission around 1050 nm, shows high temperature sensitivity (similar to 0.49% degrees C-1), and low temperature uncertainty (0.3 degrees C) as compared to the thermometric parameters defined for the 880 and 1320 nm Nd3+ 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. Nd3+ doped LiLuF4 RENPs represent a significant improvement for Nd3+ based single-band photoluminescence nanothermometry, with the possibility of its integration within more sophisticated multifunctional theranostic nanostructures.