An Advanced Thermal Decomposition Method to Produce Magnetic Nanoparticles with Ultrahigh Heating Efficiency for Systemic Magnetic Hyperthermia

Due to the limited heating efficiency of available magnetic nanoparticles, it is difficult to achieve therapeutic temperatures above 44 °C in relatively inaccessible tumors during magnetic hyperthermia following systemic administration of nanoparticles at clinical dosage (≤10 mg kg⁻¹). To address this, a method for the preparation of magnetic nanoparticles with ultrahigh heating capacity in the presence of an alternating magnetic field (AMF) is presented. The low nitrogen flow rate of 10 mL min⁻¹ during the thermal decomposition reaction results in cobalt-doped nanoparticles with a magnetite (Fe₃O₄) core and a maghemite (γ-Fe₂O₃) shell that exhibit the highest intrinsic loss power reported to date of 47.5 nH m² kg⁻¹. The heating efficiency of these nanoparticles correlates positively with increasing shell thickness, which can be controlled by the flow rate of nitrogen. Intravenous injection of nanoparticles at a low dose of 4 mg kg⁻¹ elevates intratumoral temperatures to 50 °C in mice-bearing subcutaneous and metastatic cancer grafts during exposure to AMF. This approach can also be applied to the synthesis of other metal-doped nanoparticles with core–shell structures. Consequently, this method can potentially be used for the development of novel nanoparticles with high heating performance, further advancing systemic magnetic hyperthermia for cancer treatment.