Highly Ligand‐Directed and Size‐Dependent Photothermal Properties of Magnetite Particles

The development of cancer photothermal therapies, many of which rely on photothermal agents, has received significant attention in recent years. In this work, various ligands‐stabilized magnetite (Fe3O4) particles are fabricated and utilized as a photothermal agents for in vivo tumor‐imaging‐guided photothermal therapy. Fe3O4 particles stabilized by macromolecular ligands as, e.g. polyethylene glycol (PEG), exhibit a superior and more stable photothermal effect compared to Fe3O4 particles stabilized by small molecules like citrate, due to their stronger ability of antioxidation. In addition, the photothermal effect of Fe3O4 particles is revealed to increase with size, which is attributed to the redshift of Vis‐NIR spectra. Fe3O4 particles injected intravenously into mice can be accumulated in the tumor by the application of an external magnetic field, as revealed by magnetic resonance imaging. In vivo photothermal therapy test of PEG‐stabilized Fe3O4 further achieves better tumor ablation effect. Overall, this study demonstrates efficient imaging‐guided photothermal therapy of cancer that is based on Fe3O4 particles of optimized size and with optimized ligands. It is expected that the ligand‐directed and size‐dependent photothermal effect will provide more approaches in the design of novel materials.