Defects or not defects? Or how to design 20 - 25 nm spherical iron oxide nanoparticles to harness both magnetic hyperthermia and photothermia

Abstract

Designing iron oxide nanoparticles (IONPs) to effectively combine magnetic hyperthermia (MH) and photothermia (PTT) in one IONPs formulation presents a significant challenge to ensure a multimodal therapy allowing to adapt the treatment to each patient. Recent research has highlighted the influence of factors such as size, shape, and the amount of defects on both therapeutic approaches. In this study, 20-25 nm spherical IONPs with a spinel composition were synthesized by adapting the protocol of the thermal decomposition method to control the amount of defects. By tuning different synthesis parameters such as the precursor nature, the introduction of a well-known oxidizing agent, dibenzylether (DBE), in the reaction medium , the heating rate and duration and the introduction of a nucleation step, we established thus two different synthesis protocols, one involving the use of a small amount of DBE leading to IONPs with only few defects and another that took an optimized route to oxidize the wüstite nuclei during the IONPs growth and led to IONPs displaying more structural and oxygen defects. IONPs exhibiting fewer defects displayed enhanced MH and PTT heating values and even when immobilized in a matrix, despite a decrease in MH heating values showing that they release mainly heat through the Brownian mechanism. These MH measurements have also confirmed that defects play a key role to enhance Néel relaxation. PTT measurements demonstrated higher heating values with IONPs with fewer defects and a correlation between Urbach energy and SAR values suggesting an impact of vacancies defects on PTT performances. Therefore, IONPs displaying fewer defects in our synthesis conditions appear as suitable IONPs to combine both MH and PTT treatments with high performances. These findings pave the way for promising applications in combined therapies for cancer treatment.