Experimental estimation and analysis of variance of the measured loss power of magnetic nanoparticles

Frederik Soetaert,Robert Ivkov,Sri Kamal Kandala,Andris Bakuzis

doi:10.1038/s41598-017-07088-w

Abstract

Magnetic nanoparticles dissipate heat when exposed to alternating magnetic fields (AMFs), making them suitable for cancer hyperthermia. Therapeutic heating applications demand accurate characterization of the heating power dissipated by the particles. Specific loss power (SLP) generated by magnetic nanoparticles is estimated from calorimetric heating measurements. Such measurements require adiabatic conditions, yet they are typically performed in an AMF device with non-adiabatic conditions. We have measured heating from four magnetic nanoparticle constructs using a range of frequencies (150–375 kHz) and magnetic fields (4–44 kA/m). We have extended a method developed to estimate SLP from the inherently non-adiabatic measurements, where we identify data ranges that conform to (quasi)-adiabatic conditions. Each time interval of measurement that met a predetermined criterion was used to generate a value of SLP, and the mean from all estimates was selected as the estimated SLP. Despite the application of rigorous selection criteria, measured temperature data displayed variability at specific heating loads resulting in larger variance of calculated mean SLP values. Overall, the results show a linear dependence of the SLP with AMF frequency, as anticipated by current models. Conversely, measured amplitude-dependent SLP profiles of all studied constructs conform to no predictions of current models.

Highlights

Magnetic nanoparticles (MNPs) have demonstrated utility in biomedicine due to their responsiveness to magnetic fields and generally favorable biocompatibility[1,2,3,4,5]
The validity of calorimetry rests upon two fundamental assumptions, based upon the conservation of energy, which hold for alternating magnetic fields (AMFs)-driven magnetic nanoparticle heating: 1) The system is closed; and, 2) The work done by the system is solely of magnetic nature[23, 24]
We present results of specific loss power measurements using four magnetic nanoparticle constructs that have been extensively characterized in previous studies[28, 29, 32]

Summary

Results

® Aqueous suspensions of BNF-Dextran, nanomag -D-spio (both from micromod Partikeltechnologie GmbH, Rostock, Germany), and JHU (NanoMaterials Technology, Singapore) iron oxide magnetic nanoparticles (MNPs). ® solutions (a: BNF-Dextran, b: JHU, c: nanomag -D-spio, d: MnFe2O4) at four different frequencies ranging from 150 kHz to 375 kHz. Only the mean SLP value is reported, and the error bars are the standard deviation of all possible SLP values. MnFe2O4 nanoparticles displayed SLP(H) similar to JHU nanoparticles (Fig. 3d), exhibiting a rapid ascent of heating rate at low field amplitude, consistent with the ‘soft-ferrite’ type of particle[29]. At 375 kHz an inclination towards a plateauing of SLP with amplitude, indicating possible saturation, was observed for the MnFe2O4 nanoparticles, whereas the JHU and BNF-Dextran nanoparticles did not display similar behavior at this frequency. MnFe2O4 nanoparticles display the linear trend, the measured variance was greater (Fig. 2c and d and Table 2)

Discussion

Findings

Methods