Pseudo single domain NiZn-γFe2O3colloidal superparamagnetic nanoparticles for MRI-guided hyperthermia application.

Magnetic resonance imaging (MRI)-guided magnetic nanofluid hyperthermia (MNFH) is highly desirable in cancer treatment because it can allow for diagnosis, therapeutics, and prognosis simultaneously. However, the application of currently developed iron-oxide based superparamagnetic nanoparticles (IOSPNPs) for an MRI-guided MNFH agent is technically limited by the low AC heat induction power at the physiologically tolerable range of AC magnetic field (HAC,safe), and the low transverser2-relaxivity responsible for the insufficient heating of cancers, and the low resolution of contrast imaging, respectively. Here, pseudo single domain colloidal NixZn1-x-γFe2O3(x = 0.6) superparamagnetic nanoparticle (NiZn-γFe2O3PSD-SPNP) physically and theoretically designed at theHAC,safe, specifically by the applied frequency, is proposed for a highly enhanced MRI-guided MNFH agent application. The NiZn-γFe2O3PSD-SPNP showed the superparamagnetic characteristics, significantly enhanced AC heat induction performance (ILP = 6.3 nHm2kg-1), highly improved saturation magnetization (Ms= 97 emu g-1Fe, 3.55 × 105A m-1) andr2-relaxivity (r2 = 396 mM-1s-1) that are desirable for highly efficient MRI-guided MNFH agent applications. According to the analyzed results, the remarkably enhanced effective relaxation time constant and its dependent out-of-phase magnetic susceptibility, as well as the DC/AC magnetic softness optimized by the PSD-SPNP at theHAC,safewere revealed as the main physical reason for the significance. All the fundamentalin vitroandin vivoexperimental results demonstrated that the physically designed NiZn-γFe2O3PSD-SPNP is bio-technically feasible for a highly efficient MRI-guided MNFH agent for future cancer nanomedicine.

Direct visualization of the thermomagnetic behavior of pseudo-single-domain magnetite particles.

The study of the paleomagnetic signal recorded by rocks allows scientists to understand Earth's past magnetic field and the formation of the geodynamo. The magnetic recording fidelity of this signal is dependent on the magnetic domain state it adopts. The most prevalent example found in nature is the pseudo-single-domain (PSD) structure, yet its recording fidelity is poorly understood. Here, the thermoremanent behavior of PSD magnetite (Fe3O4) particles, which dominate the magnetic signatures of many rock lithologies, is investigated using electron holography. This study provides spatially resolved magnetic information from individual Fe3O4 grains as a function of temperature, which has been previously inaccessible. A small exemplar Fe3O4 grain (~150 nm) exhibits dynamic movement of its magnetic vortex structure above 400°C, recovering its original state upon cooling, whereas a larger exemplar Fe3O4 grain (~250 nm) is shown to retain its vortex state on heating to 550°C, close to the Curie temperature of 580°C. Hence, we demonstrate that Fe3O4 grains containing vortex structures are indeed reliable recorders of paleodirectional and paleointensity information, and the presence of PSD magnetic signals does not preclude the successful recovery of paleomagnetic signals.

Paleomagnetic recording fidelity of nonideal magnetic systems.

A suite of near-identical magnetite nanodot samples produced by electron-beam lithography have been used to test the thermomagnetic recording fidelity of particles in the 74-333 nm size range; the grain size range most commonly found in rocks. In addition to controlled grain size, the samples had identical particle spacings, meaning that intergrain magnetostatic interactions could be controlled. Their magnetic hysteresis parameters were indicative of particles thought not to be ideal magnetic recorders; however, the samples were found to be excellent thermomagnetic recorders of the magnetic field direction. They were also found to be relatively good recorders of the field intensity in a standard paleointensity experiment. The samples' intensities were all within ∼15% of the expected answer and the mean of the samples within 3% of the actual field. These nonideal magnetic systems have been shown to be reliable records of the geomagnetic field in terms of both direction and intensity even though their magnetic hysteresis characteristics indicate less than ideal magnetic grains. KEY POINTS: Nonideal magnetic systems accurately record field directionWeak-field remanences more stable than strong-field remanences.