Magnetic Nanoparticles as Label‐Free Dual‐Function Nanoheaters and Nanothermometers

Heat generation and temperature reading at the nanoscale are highly relevant for thermal therapeutic approaches, motivating the development of dual-function nanoplatforms that integrate heating and thermometry. However, most nanoheater-nanothermometer systems rely on specifically engineered materials or complex readout schemes, which can limit translational potential. Here, we present a methodology for extracting temperature information from dynamical magnetization measurements of cobalt ferrite magnetic nanoflowers. We establish a quantitative relationship between temperature and the dynamic magnetic response of the nanoparticles through Brownian relaxation, mediated by the thermal dependence of water viscosity. This link between magnetization dynamics and thermally driven nanoparticle diffusion enables temperature changes to be monitored through variations in magnetization cycles measured under alternating magnetic fields. Importantly, this thermometric functionality is retained after surface functionalization and under controlled changes in medium composition. Furthermore, the same nanocrystal agent is used to generate heat under near-infrared irradiation and report temperature changes through magnetization dynamics. Together, these results establish cobalt ferrite magnetic nanoparticles as a label-free platform for combined heat generation and intrinsic temperature readout, opening a route toward real-time thermal monitoring in nanoscale heating applications.