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

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.

Evaluation of magnetic nanoparticles for magnetic fluid hyperthermia

“…This study [59] also compared heating properties of nanoparticles within an aqueous environment, inside cells, and within tumors, and showed that MNPs lose heating power when internalized by cells. Despite similarities to ILP and SAR values from the literature, the experimental set-ups for heating measurements can have potential sources of error [18,60,61], with sample volume being one of them. In a few studies [18,60] it was shown that decreasing sample volumes results in lower SAR values.…”

“…The first two methods, ISM and CSM, are linear approximations of the phenomenological BLM and can be used in certain situations. ISM would be accurate for adiabatic measurements with no chemical or physical changes within the samples [61].…”

“…It should also be noted that different time intervals for ISM-SAR calculation have been used in literature and can affect its accuracy [18,61]. In this study, we chose 60 s time interval since the initial temperature rise was linear within this region for most MNPs.…”

“…A study by Bordelon et al [56] has established a protocol for empirically determining appropriate fitting intervals for the ISM to achieve results comparable to the BLM; however, it was only performed for three MNP types and would need to be studied in more detail to ensure it will be accurate for variety of MNPs. This method was further developed by Soetart et al [61] to identify time ranges of heating which satisfy quasi-adiabatic conditions and it was discussed that an arbitrary choice of a single time interval will likely result in unreliable results. SAR calculation methods are also evaluated by Wildeboer et al [12] and they found BLM and CSM to give more accurate SAR values than the ISM.…”

The Potential Biomedical Application of NiCu Magnetic Nanoparticles

“…Nevertheless, another important factor to be considered when applying a novel formulation for MH is the overall concentration of the respective NPs at the tumor site [50,51]. Specifically, NPs with a low specific loss power (SLP) need to be more concentrated in the tumor, with the consequent disadvantages of bioaccumulation and long-term toxicity [52,53].…”