Sensitizer-Passivated Magnetic Ferrite/Eu3+-Doped Oxide Nanocomposite: A Novel Luminescent Probe for Facile Bioimaging with Superior Magnetic Hyperthermia Performance

Abstract

In this work, we design a magneto-luminescent nanocomposite system comprised of magnetic ferrite nanoparticles and a Ln³⁺-based luminophore, with an excellent balance of lanthanide emission and induction heating capacity, which remains a challenge. At first, we encapsulate Zn-doped ferrite nanoparticles (Zn_xFe_3–xO₄; x ≈ 0.3) of size ∼20 nm within thin layers of silica and amorphous Gd₂O₃ doped with Eu³⁺ (5 atom %), respectively. Then, we activate the Eu³⁺ luminescence in Zn_xFe_3–xO₄@SiO₂@Gd₂O₃:Eu³⁺ (Eu-ZFO) nanocomposites using the organic ligand 2-thenoyltrifluoroacetone (TTA)-mediated surface passivation approach. We find that the resulting nanocomposites (Eu-ZFO-TTA NCs) display bright red Eu³⁺-emission (quantum yield 9.3%) under near-UV excitation with a long emission lifetime (0.181 ms) and high stability against photoluminescence leakage. Moreover, we witness a significant magnetization (39.3 emu/g) and, thereby, a remarkably high induction heating capacity of Eu-ZFO-TTA NCs than the reported magneto-luminescent nanocomposites. This is depicted by the intrinsic loss power of Eu-ZFO-TTA NCs as high as 11 nH m²/kg in an aqueous dispersion under an AC magnetic field (AMF) of 12 kA/m, 335 kHz. Finally, we examine the bioimaging and AMF-induced hyperthermia performance of the nanocomposites in vitro on human lung adenocarcinoma A549 cells using a live cell confocal fluorescence microscopy study and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. We find the Eu-ZFO-TTA NCs highly biocompatible (IC₅₀ = approximately 800 μg/mL), and their intense red emission is very effective for monitoring their cellular internalization. Moreover, only 200 μg/mL dose of NCs is sufficient to induce significant cell death (>75%) under AMF. Besides, we perform a hemolysis test and observe that our NCs exhibit a high hemocompatibility at the 200 μg/mL dose (<5% hemolysis). These outcomes imply an immense prospect for Eu-ZFO-TTA NCs to replace the reported magneto-luminescent nanomaterials for future in vivo optical image-guided low-field magnetic hyperthermia therapy of cancer.