Magnetic nanoparticles for power absorption: Optimizing size, shape and magnetic properties

Abstract

We present a study on the magnetic properties of naked and silica-coated Fe 3 O 4 nanoparticles with sizes between 5 and 110 nm. Their efficiency as heating agents was assessed through specific power absorption (SPA) measurements as a function of particle size and shape. The results show a strong dependence of the SPA with the particle size, with a maximum around 30 nm, as expected for a Néel relaxation mechanism in single-domain particles. The SiO 2 shell thickness was found to play an important role in the SPA mechanism by hindering the heat outflow, thus decreasing the heating efficiency. It is concluded that a compromise between good heating efficiency and surface functionality for biomedical purposes can be attained by making the SiO 2 functional coating as thin as possible. 81.16.Be, 75.50.+a PACS:

Application of magnetically induced hyperthermia in the model protozoan Crithidia fasciculata as a potential therapy against parasitic infections

“…23 This synthesis route resulted in magnetic colloids with an isoelectric point of 5.0, electrostatically stabilized due to adsorption of SO 4 2-groups on the particle surface. The ability to dissipate heat under a TVMF of any type of MNP is measured by the specific power absorption given in watts per gram of magnetic material, which for the present MNPs and experimental conditions (f = 249 kHz, H = 13 kA/m) was found to be 83.6 W/g, 22 comparable with other specific power absorption values reported in the literature for Fe 3 O 4 particles of similar size. [24][25][26] The selection of MNPs was made based on the known dependence of specific power absorption values on an average particle size and size distribution.…”

“…22 The magnetic colloids were composed of cubic Fe 3 O 4 nanoparticles with an average diameter of 30 ± 8 nm and saturation magnetization at room temperature of 85 emu/g, which is close to that of the bulk magnetite magnetization. 23 This synthesis route resulted in magnetic colloids with an isoelectric point of 5.0, electrostatically stabilized due to adsorption of SO 4 2-groups on the particle surface.…”

Long‐Term Stability and Reproducibility of Magnetic Colloids Are Key Issues for Steady Values of Specific Power Absorption over Time

“…MNPs with broad ranges of sizes have different saturation magnetization values and anisotropies reducing the maximum SPA. [29] Figure 1 Regarding magnetic hyperthermia applications, a strict reproducibility of the final particle size and size distribution is a key consideration, since the heat generated by an ensemble of MNPs in a magnetic colloid can substantially change by tiny shifts in the average particle size [30] [31] or size distribution. [16] These variations hinder the possibility of a standardized response of a given material, resulting in large variations of the thermal doses under fixed experimental conditions.…”

Superparamagnetic iron oxide nanoparticles: magnetic nanoplatforms as drug carriers

“…Coating tends to decrease heating efficiency, hence should be kept to a minimum. 104 Magnetoliposomes have also emerged as an effective tool for producing localized hyperthermia together with delivery of encapsulated drugs to the target site, resulting in the destruction of cancerous cells. In order to achieve targeted delivery of methotrexate to skeletal muscle tissue, Zhua et al prepared thermosensitive magnetoliposomes capable of liberating more than 80% of the encapsulated methotrexate within 30 minutes when the environmental temperature was increased from 37°C to 41°C.…”