Temperature-Dependent Luminescence of Nd³⁺-Doped Carbon Nanodots for Nanothermometry

Noncontact optical nanothermometers operating within the biological transparency windows are required to study temperature-sensitive biological phenomena at the nanoscale. Nanoparticles containing rare-earth ions such as Nd³⁺ have been reported to be efficient luminescence-based ratiometric thermometers, however often limited by poor water solubility and concentration-related quenching effects. Herein, we introduce a new type of nanothermometer, obtained by employing low-dimensional carbon nanodots (CNDs) as matrices to host Nd³⁺ ions (NdCNDs). By means of a one-pot procedure, small (∼7-12 nm), water-soluble nanoparticles were obtained, with high (15 wt %) Nd³⁺ loading. This stable metal-CND system features temperature-dependent photoluminescence in the second biological window (BW II) upon irradiation at 808 nm, thereby allowing accurate and reversible (heating/cooling) temperature measurements with good sensitivity and thermal resolution. The system possesses remarkable biocompatibility in vitro and promising performance at a high penetration depth in tissue models.