Nanoscale thermal effect of ferrimagnetic vortex-domain iron oxide nanorings

The nanoscale thermal effect of ferrimagnetic vortex-domain iron oxide nanorings (FVIOs) was measured when exposed to an alternating magnetic field. A molecular temperature probe (fluorescein isomer I, FI) was attached to a thermo-sensitive molecule (4,4′-Azobis (4-cyanovaleric acid, AZO), then the molecule was bound to the nanoparticle surface through poly (ethylene glycol) (PEG, M w = 1000, 2000, 5000 Da) spacers of different molecular weights. The magnetothermal effect induced the thermal decomposition of AZO driving the release of FI which was monitored by the photoluminescence method. It was found that the effective local temperature ( T eff ) decreased with the increase of M w (PEG) and increased with the rise in field amplitudes B, and the temperature was found in a linear relationship with the applied magnetic field at all distances. The significant local heating temperature ( T ) rose to 60.3 °C when d = 0 of FVIOs, where d is the distance of the AZO-FI end group to the surface, while it fell exponentially with the increasing distance. The nanoscale thermal effect of the 20 nm superparamagnetic iron oxide nanoparticles (SPIOs) was also studied. The results revealed that FVIOs have much higher nanometer local heat than SPIOs for all the applied magnetic field amplitudes. These findings were then applied in the enzyme activity regulation experiment of FVIOs and SPIOs. The results indicated that glucose oxidase (GOD) had higher enzyme activity after nano-magnetothermal stimulation of FVIOs.