Nanoscale temperature determination of individual gold nano-heaters in colloids by confocal dynamic light scattering

Accurate temperature determination at the nanoscale is crucial for understanding and optimizing the photothermal properties of plasmonic nanoparticles (NPs). Here, we introduce confocal dynamic light scattering (confocal DLS) as a novel method for in-situ measurement of the temperature of individual colloidal NPs. By coupling tightly focused heating-probe configuration with single-particle DLS, we quantify NPs heating at their surface from their Brownian motion, exploiting the temperature dependence of the solvent viscosity. Experiments on Au NPs (20-50 nm) reveal excellent agreement with the hot Brownian motion theory, enabling reliable temperature increases determination up to ∼ 150 K, without any adjustable parameters. Importantly, the method extends to Au@SiO₂ core-shell nano-heaters, where a transition from the high-density to the low-density hot Brownian motion regime is experimentally observed for the first time, demonstrating that the density ratio between the NPs and the solvent governs the motion of the heated NPs. Confocal DLS thus provides unprecedented access to the photothermal response of nanoscale heaters at the single-particle level, including mesoporous core-shell architectures, paving the way for applications in nanoscale catalysis, thermally responsive nanomaterials and controlled drug release.