Ligand’s Role in the Near-Infrared Light-to-Heat Conversion of Au₂₅ Nanoclusters Acting as a Photothermal Agent and Luminescent Lifetime-Based Nanothermometer

Non-invasive photothermal therapy (PTT) using nanoscale materials is a promising therapeutic method for cancer treatment, where real-time temperature monitoring is critical for clinical efficacy. This study employs atomically precise Au₂₅ nanoclusters (NCs) that exhibit photothermal activities under near-infrared (NIR) excitation and systematically investigates how the light-to-heat conversion efficiency can be modulated by changing the surface ligands of the Au₂₅ NCs. The photothermal efficiency of these Au₂₅ NCs can be correlated to their photoluminescence (PL) lifetime, which is strongly influenced by the surface-capping ligands. Remarkably, by rigidifying the surface ligands within the protein scaffold, photothermal conversion efficiency of the NCs is further strikingly enhanced. Furthermore, we highlight the bimodal role of Au₂₅ NCs as photothermal agents and luminescent lifetime-based nanothermometer. Indeed, Au₂₅ NCs exhibit a linear correlation between the lifetime and temperature, enabling real-time monitoring of both local (in the NCs) and global (in the solutions) temperature changes during PTT.