Effect of magnetic dipolar interactions on temperature dependent magnetic hyperthermia in ferrofluids

Abstract

Magnetic hyperthermia (MHT), where localized heating is generated when magnetic nanoparticles (MNPs) are subjected to a radiofrequency magnetic field, has a great potential as a non-invasive cancer therapy treatment. The efficiency of heat generation depends on the magnetic properties of MNPs, such as saturation magnetization (Ms) and magnetic anisotropy (K), as well as the particle size distribution and magnetic dipolar interactions. We have investigated MHT in two Fe3O4 ferrofluids prepared by co-precipitation (CP) and hydrothermal (HT) synthesis methods showing similar physical particle size distribution (14 ± 4 nm) and saturation magnetization (70 ± 2 emu/g of Fe3O4) but very different specific absorption rates (SAR) of ∼110 W/g and ∼40 W/g at room temperature (measured with an ac magnetic field amplitude of 240 Oe and a frequency of 375 kHz). This observed reduction in SAR has been explained by taking into account the dipolar interactions and the distribution of the magnetic core size of MNPs in ferrofluids. The HT ferrofluid shows a higher effective dipolar interaction and a wider distribution of the magnetic core size of MNPs compared to those of the CP ferrofluid. We have fitted the temperature dependent SAR data using the linear response theory, incorporating an effective dipolar interaction, to determine the magnetic anisotropy constant of MNPs prepared by CP (22 ± 2 kJ/m3) and HT (26 ± 2 kJ/m3) synthesis methods. These values are in good agreement with the magnetic anisotropy constant determined using frequency and temperature dependent magnetic susceptibility data obtained on powder samples.

Gd-Doped Superparamagnetic Magnetite Nanoparticles for Potential Cancer Theranostics

“…[140]. The solid lines in Figure 7(b) are the best fits to the experimental SAR data, using the particle size distribution parameters and T * values given in 4 is probably offset by a larger particle size in this sample, as the SAR would increase with increasing particle size up to a critical size [140]. By fine-tuning the composition of Gd-doped Fe 3 O 4 nanoparticles, we may achieve a higher SAR value.…”

“…Gd-Doped Superparamagnetic Magnetite Nanoparticles for Potential Cancer Theranostics http://dx.doi.org/10.5772/intechopen.68219 93 observed XRD data, and it was necessary to introduce the magnetic dipolar interaction effects through a phenomenological temperature, T * , as described in our recent work [140]. The bestfit parameters for the two samples are shown in Table 2, and Figure 6 shows the fitted data.…”

“…It has been shown that the dipolar interactions among the MNP affect the SAR value drastically and can be exploited to optimize SAR [136][137][138][139]. A mean-field approximation method has been used to account for effects of interactions on SAR for a collection of monodisperse MNP [138,139], and we have used this approach to explain the very different observed SAR values for similar size particles prepared by two different methods of preparation [140].…”

“…3 was mixed in a molar ratio of 1.00:1.925:0.075 in 25-ml volume followed by the addition of 250 ml of 1 M NH 4 OH. The synthesized nanoparticles were then coated with dextran according to the method outlined by Arachchige et al [140]. From the structural investigation, it was observed that Gd doping does not alter the Fe 3 O 4 crystal structure significantly (Figure 4).…”

“…The black line shows the theoretical fitting of the experimental data with the linear response theory [160]. [140]. The solid lines in Figure 7(b) are the best fits to the experimental SAR data, using the particle size distribution parameters and T * values given in 4 is probably offset by a larger particle size in this sample, as the SAR would increase with increasing particle size up to a critical size [140].…”