Zn_xMn_1–XFe₂O₄@SiO₂:zNd³⁺ Core–Shell Nanoparticles for Low-Field Magnetic Hyperthermia and Enhanced Photothermal Therapy with the Potential for Nanothermometry

Multifunctional magnetic nanoparticles (NPs) that can generate and monitor heat (in real-time) during thermal therapy are a major challenge in nanomedicine. Here, we report a trimodal system combining magnetic NP hyperthermia (MNH), photothermal therapy (PTT), and luminescent nanothermometry (LNT) properties with an all-in-one nanoplatform. Zinc–manganese ferrite NPs were optimized focusing on low field MNH, where Zn0.3Mn0.7Fe2O4 proved as a competitive nanoheater at clinically relevant conditions. Further, SiO2-coated Zn0.3Mn0.7Fe2O4/cit. with embedded Nd3+ (Zn0.3Mn0.7Fe2O4@SiO2:Nd) NPs were prepared for the potency of multifunctionality as LNT and enhanced PTT. Photothermal conversion efficiency (PCE), at low laser power conditions (1.5 W/cm2), varied from 17% for silica-coated magnetic NPs to 24% after embedding 1 mmol of Nd3+ in the SiO2 matrix. Increasing laser power to 11.8 W/cm2 decreased the PCE of Zn0.3Mn0.7Fe2O4@SiO2:Nd to 9%, but this deleterious effect was reduced significantly by the shell engineering strategy, that is, increasing the shell thickness Zn0.3Mn0.7Fe2O4@ SiO2@SiO2:Nd that maintained a PCE value of 18%. Additionally, as a potential nanothermometer, with excitation around 800 nm and emission at the second biological window, the thermal sensitivity of the system was found to be ∼1.1 % K–1 at 300 K (27 °C), ∼ 1.4% K–1 at 316 K (43 °C), and ∼1.5% K–1 at 319 K (46 °C). Additionally, simultaneous heating effects due to magnetic fields and photoexcitation (808 nm) on Zn0.3Mn0.7Fe2O4@SiO2@SiO2:Nd show synergy effects between MNH and PTT. Because of the high hemolytic activity toward the red blood cells due to the SiO2 layer, we also demonstrate that surface coating the nanocarrier with bovine serum albumin drastically reduced the hemolytic activity providing a capability for future in vivo applications with this multifunctional nanocarrier.