Remote non-invasive nanothermometry based on opto-magnetic detection

As an emerging sensing paradigm for magnetic nanoparticles (MNPs), opto-magnetic detection offers distinct advantages over conventional magnetic methods, including remote operation and non-invasiveness. Optical readout enables stable monitoring of the dynamic response of MNPs under magnetic excitation and has recently shown promise for rapid biomolecular detection. The core principle of opto-magnetic detection is the magnetic-field-induced modulation of the extinction cross section of MNPs, thereby transducing physicochemical information from the local particle environment via the dynamic characteristics of Brownian relaxation. In this work, we adopt the Cole–Cole model to effectively describe the thermal motion of particles arising from the interplay between magnetic potential energy and thermal energy. Furthermore, exploiting the relationship between the second harmonic phase and the Brownian relaxation-time spectrum, we propose an opto-magnetic thermometry method. By employing a Cole–Cole-derived Cauchy-type relaxation-time distribution, we achieve high-precision temperature measurements over the range of 308–318 K, with a root mean square error of only 0.03 K. This approach provides technical support for opto-magnetic thermometry in applications such as intracellular temperature imaging, real-time thermotherapy monitoring, and point-of-care testing.