Multiparametric Magnetic Particle Spectroscopy of CoFe₂O₄ Nanoparticles in Viscous Media

Abstract

A detailed signal generation of the magnetization response of magnetic nanoparticles (MNPs) as a result of externally applied magnetic fields with flux densities of several millitesla is of high interest for biomedical applications such as magnetic resonance imaging or magnetic particle imaging (MPI). Although, MNPs are already frequently used as contrast agents or tracer materials, experimental data are rarely compared to model predictions because of distinct deviations. In this article, we use a customized Brownian-dominated CoFe 2 O 4 particle system to compare experimental magnetic particle spectroscopy data with Fokker−Planck simulations considering the Brownian relaxation. The influences of viscosity, size distribution, excitation frequency, and field amplitude are studied. We show that the effective magnetic moment and cluster sizes can be determined using a sample viscosity series. As introduced, such particle systems can serve as model systems to evaluate mathematical expressions and to study dependences on physical influencing factors. Investigations of defined MNP systems and detailed characterizations enable a wide field of improved diagnosis and therapy applications, for example, mobility MPI and magnetic hyperthermia.

Biophysical Characterization of (Silica-coated) Cobalt Ferrite Nanoparticles for Hyperthermia Treatment

“…As described by Draack et al [22], the particle system in this work is dominated by the Brownian relaxation mechanism, which is important for an effective heating in hyperthermia [8,23]. From Equation 1, the imaginary part of the ACS is at maximum at ωτ = 1, i.e., the Brownian relaxation time can be calculated from the frequency of the Χ″ maximum.…”

A novel characterization technique for superparamagnetic iron oxide nanoparticles: The superparamagnetic quantifier, compared with magnetic particle spectroscopy

“…17 Later, MPS has been used in many biological applications, including measurements on SPIONs in different biological environments, 18 measurements on changes in the magnetization behavior during cellular uptake of SPIONs, 19 and viscosity measurements. [20][21][22] In many applications, the focus is on the harmonics spectrum. However, in this paper, the focus is on the time signal, which contains both the fundamental frequency and higher harmonics.…”

“…Many parameter values can be deduced from the curve measured in either the SPaQ or MPS, such as the core diameter, hydrodynamic diameter, and anisotropy of the particles, 23 but information about the environment of the particles can also be obtained. [20][21][22] During the design of SPIONs, it is essential to apply a consistent characterization technique. As a result, it will become possible to check quickly what the effect is of a change in the design process.…”

Simultaneous Coercivity and Size Determination of Magnetic Nanoparticles

“…In DC magnetometry (DCM) [ 14 ], the response to a DC magnetic field is recorded, while in magnetorelaxometry (MRX) [ 15 , 16 ], the MNP’s relaxation is measured after the application of a pulsed DC magnetic field. In AC susceptibility (ACS) [ 17 , 18 ] and Magnetic Particle Spectroscopy (MPS) [ 19 , 20 ], particle properties are retrieved by measuring their response to specific AC fields. Recently, thermal noise magnetometry [ 21 , 22 ] was introduced as a means to overcome possible magnetic field-induced changes to the MNP’s properties (e.g., particle clustering) by measuring the nanoparticles’ magnetic dynamics in the absence of magnetic fields.…”