Alternating Current Biosusceptometry for Real-Time Magnetic Nanothermometry in Photothermal Therapy

Photothermal therapy (PTT) is a promising approach for cancer treatment, where nanostructures generate heat by absorbing energy from nonionizing radiation at the near-infrared region (NIR) without damaging healthy tissues. However, real-time temperature monitoring during PTT remains a significant challenge, especially due to the difficulty of accessing the treated region without interfering with the biological microenvironment. In this study, we developed an Alternating Current Biosusceptometry (ACB) sensor for real-time thermal monitoring of media containing magnetic nanoparticles (MnFe₂O₄) capable of generating heat under NIR laser irradiation. The nanoparticles were analyzed in both stable magnetic fluid and dry powder forms. The signals acquired by the ACB system — including linear magnetic susceptibility and signal phase — exhibited temperature-dependent variations during PTT. These parameters increased or decreased depending on the structural arrangement of the nanoparticles, supporting the hypothesis that ACB sensors hold great potential for real-time thermal monitoring during PTT involving magnetic nanoparticles. Moreover, the results indicated that the physicochemical properties of the magnetic tracers directly influence the magnetic nanothermometry response profile. A example is the presence of dipolar interactions between particles, which promote nanoparticle aggregation and significantly affect the detected magnetic signal. The results highlight the potential of ACB as a non-invasive and sensitive technique for magnetic nanothermometry, with applicability in nanoparticle-assisted thermal therapies. Future development stages will focus on the application of ACB sensors in cell-based studies, aiming at thermal monitoring mediated by magnetic nanoparticles and expanding the use of magnetic nanothermometry in biomedical contexts.