Fe₃O₄@polydopamine Composite Theranostic Superparticles Employing Preassembled Fe₃O₄ Nanoparticles as the Core

Iron oxide (Fe₃O₄), polydopamine (PDA), and in particular their composites are examples of the safest nanomaterials for developing multifunctional nanodevices to perform noninvasive tumor diagnosis and therapy. However, the structures and performances of Fe₃O₄–PDA nanocomposites should be further perfected to enhance the theranostic efficiency. In this work, we demonstrate the fabrication of PDA-capped Fe₃O₄ (Fe₃O₄@PDA) superparticles (SPs) employing preassembled Fe₃O₄ nanoparticles (NPs) as the cores. Owing to the collective effect of preassembled Fe₃O₄ NPs, the superparamagnetism and photothermal performance of Fe₃O₄@PDA SPs are greatly enhanced, thus producing nanodevices with improved magnetic resonance imaging (MRI)-guided photothermal efficiency. Systematical studies reveal that the molar extinction coefficient of the as-assembled Fe₃O₄ SPs is 3 orders of magnitude higher than that of individual Fe₃O₄ NPs. Also due to the high aggregation degree of Fe₃O₄ NPs, the T₂-weighted MRI contrast is greatly enhanced for the SPs with r₂ relaxivity of 230.5 mM^–1 s^–1, which is ∼2.5 times larger than that of individual Fe₃O₄ NPs. The photothermal stability, physiological stability, and biocompatibility, as well as the photothermal performance of Fe₃O₄ SPs, are further improved by enveloping with PDA shell.