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Multifunctional nanoparticles with a magnetic core and gold shell structures are emerging multi-modal imaging probes for disease diagnosis, image-guided therapy, and theranostic applications. Owing to their multi-functional magnetic and plasmonic properties, these nanoparticles can be used as contrast agents in multiple complementary imaging modalities. Magnetic particle imaging (MPI) is a new pre-clinical imaging system that enables real-time imaging with high sensitivity and spatial resolution by detecting the dynamic responses of nanoparticle tracers. In this study, we evaluated the dynamic magnetic properties and MPI imaging performances of core-shell nanoparticles with a magnetic core coated with a gold shell. A change in AC hysteresis loops was detected before and after the formation of the gold shell on magnetic core nanoparticles, suggesting the influence of the core-shell interfacial effect on their dynamic magnetic properties. This alteration in the dynamic responses resulted in an enhancement of the MPI imaging capacity of magnetic nanoparticles. The gold shell coating also enabled a simple and effective functionalization of the nanoparticles with a brain glioma targeting ligand. The enhanced MPI imaging capacity and effective functionality suggest the potential application of the magnetic-gold core-shell nanoparticles for MPI disease diagnostics.

Correction for ‘Dynamic magnetic characterization and magnetic particle imaging enhancement of magnetic-gold core–shell nanoparticles’ by Asahi Tomitaka et al., Nanoscale, 2019, 11, 6489–6496, DOI: 10.1039/C9NR00242A.

The second harmonic signal of a magnetic nanoparticle in an oscillating magnetic field was enhanced, by applying a static bias field. To promote the second harmonic signal, the oscillating field was applied perpendicular to the signal detection and static bias field. The second harmonic signal, detected in this study, was significantly higher than that of the third harmonic signal detected without a static bias field. It was also significantly higher than that of the second harmonic signal with the static bias and oscillating drive field parallel to the signal detection direction, as in the conventional setup of previous studies. The second harmonic signal dependence on the intensity of the static bias field showed that the signal intensity had a maximal value beyond the field free point (FFP), despite the maximal third harmonic existing within the FFP. In our system, the odd numbered harmonics, including the fundamental harmonic, were no longer detected. This is because the fundamental signal had a frequency twice that of the applied oscillating field. This may contribute to a significantly higher signal to noise ratio for magnetic particle imaging (MPI). In addition, the full width at half maximum associated with MPI resolution was constant with drive field amplitude, which contributes to high signal intensity and resolution, concurrently.

Magnetic hyperthermia is a promising application of magnetic nanoparticles (MNPs) in cancer therapy. It is important to consider and optimize the parameters that affect heat dissipation, such as particle diameters, structures, and surface coatings. In this study, we measured the magnetic properties of two superparamagnetic nanoparticles under DC and AC magnetic fields. Resovist is approved to be used as a magnetic resonance imaging contrast agent. CMEADM-033-02, with the blood-pooling property and biocompatibility, exhibits high magnetization. The blood-pooling property makes it easier for MNPs to accumulate in tumors and tissue. While preparing samples, we aligned the easy axis of the samples using a DC magnetic field to enhance heat dissipation. We discussed the magnetic property in terms of magnetic relaxation associated with anisotropy energy. We observed that the peak frequency of Neel relaxation was considerably shifted owing to effectively changed anisotropy by the alignment of the easy axis. However, the change in the peak frequency of Neel relaxation could not be directly confirmed. Furthermore, we calculated the intrinsic loss power (ILP) and specific loss power (SLP) for heat dissipation from the areas of AC magnetization curves and estimated the SLP at 1 MHz to compare with the high heating characteristic of ILP that has been reported in a conventional study. We achieved equivalent ILP for heat dissipation as that reported in the study by aligning the easy axis of the MNPs with the blood-pooling property under a therapeutic condition.