Generalized Scaling and the Master Variable for Brownian Magnetic Nanoparticle Dynamics

Hysteresis losses in magnetic nanoparticles constitute the basis of magnetic hyperthermia for delivering a local thermal stress. Nevertheless, this therapeutic modality is only to be realised through a careful appraisal of the best possible intrinsic and extrinsic conditions to the nanoparticles for which they maximise and preserve their heating capabilities. Low frequency (100 kHz) hysteresis loops accurately probe the dynamical magnetic response of magnetic nanoparticles in a more reliable manner than calorimetry measurements, providing conclusive quantitative data under different experimental conditions. We consider here a set of iron oxide or cobalt ferrite nanocubes of different sizes, through which we experimentally and theoretically study the influence of the viscosity of the medium on the low frequency hysteresis loops of magnetic colloids, and hence their ability to produce and dissipate heat to the surroundings. We analyse the role of nanoparticle size, size distribution, chemical composition, and field intensity in making the magnetisation dynamics sensitive to viscosity. Numerical simulations using the stochastic Landau-Lifshitz-Gilbert equation model the experimental observations in excellent agreement. These results represent an important contribution towards predicting viscosity effects and hence to maximise heat dissipation from magnetic nanoparticles regardless of the environment.

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Unraveling viscosity effects on the hysteresis losses of magnetic nanocubes

Cabrera

Lak

Yonetani

et al. 2017

Nanoscale

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One-sided multidimensional statistical significance testing: a new method of calculating the statistical significance of spectra used to demonstrate magnetic nanoparticle sensitivity*

Weaver¹,

Weaver²,

Ness³

et al. 2022

J. Phys. D: Appl. Phys.

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Estimating the statistical significance of the difference between two spectra or series is challenging. Multivariate significance tests exist but the limitations preclude their use in many common cases; e.g., one-sided testing, unequal variance and when few repetitions are acquired all of which are required in magnetic spectroscopy of nanoparticle Brownian motion (MSB). We introduce a test, termed the T-S test, that is powerful, exact (type I error is the selected significance threshold when the null hypothesis is true) and flexible. It is flexible enough to be one or two sided and the one sided version can specify arbitrary regions where each spectra should be larger. The T-S test takes the one or two sided p-value at each frequency and combines them using Stouffer’s method. We evaluated it using simulated spectra and measured MSB spectra. For the single sided version, mean of the spectrum, A-T, was used as a reference; the T-S test is as powerful when the variance at each frequency is uniform and outperforms when the noise power is not uniform. For the two sided version, the Hotelling T2 two-sided multivariate test was used as a reference; the two-sided T-S test is only slightly less powerful for large numbers of repetitions and outperforms rather dramatically for small numbers of repetitions. The T-S test was used to estimate the sensitivity of our current MSB spectrometer showing 1 nanogram sensitivity. Using eight repetitions the T-S test allowed 15 pM concentrations of mouse IL-6 to be identified while the mean of the spectra only identified 76 pM.

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Generalized Scaling and the Master Variable for Brownian Magnetic Nanoparticle Dynamics

Cited by 2 publications

References 46 publications

Unraveling viscosity effects on the hysteresis losses of magnetic nanocubes

Unraveling viscosity effects on the hysteresis losses of magnetic nanocubes

One-sided multidimensional statistical significance testing: a new method of calculating the statistical significance of spectra used to demonstrate magnetic nanoparticle sensitivity*

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