Boosting the sensitivity of Nd3+-based luminescent nanothermometers

Luminescence thermal sensing and deep-tissue imaging using nanomaterials operating within the first biological window (ca. 700-980 nm) are of great interest, prompted by the ever-growing demands in the fields of nanotechnology and nanomedicine. Here, we show that (Gd1-xNdx)(2)O-3 (x = 0.009, 0.024 and 0.049) nanorods exhibit one of the highest thermal sensitivity and temperature uncertainty reported so far (1.75 +/- 0.04% K-1 and 0.14 +/- 0.05 K, respectively) for a nanothermometer operating in the first transparent near infrared window at temperatures in the physiological range. This sensitivity value is achieved using a common R928 photomultiplier tube that allows defining the thermometric parameter as the integrated intensity ratio between the F-4(5/2) -> I-4(9/2) and F-4(3/2) -> I-4(9/2) transitions (with an energy difference between the barycentres of the two transitions > 1000 cm(-1)). Moreover, the measured sensitivity is one order of magnitude higher than the values reported so far for Nd3+-based nanothermometers enlarging, therefore, the potential of using Nd3+ ions in luminescence thermal sensing and deep-tissue imaging.