Magnetic particle spectroscopy (MPS), also called magnetization response spectroscopy (MRS), is a versatile measurement tool derived from magnetic particle imaging (MPI). It can be interpreted as a...

Magnetic Particle Spectroscopy: A Short Review of Applications Using Magnetic Nanoparticles

Magnetic particle imaging (MPI) has recently emerged as a promising non-invasive imaging technique because of its signal linearly propotional to the tracer mass, ability to generate positive contrast, low tissue background, unlimited tissue penetration depth, and lack of ionizing radiation. The sensitivity and resolution of MPI are highly dependent on the properties of magnetic nanoparticles (MNPs), and extensive research efforts have been focused on the design and synthesis of tracers. This review examines parameters that dictate the performance of MNPs, including size, shape, composition, surface property, crystallinity, the surrounding environment, and aggregation state to provide guidance for engineering MPI tracers with better performance. Finally, we discuss applications of MPI imaging and its challenges and perspectives in clinical translation.

Engineering of magnetic nanoparticles as magnetic particle imaging tracers

Magnetite (Fe3O4) particles with a diameter around 10 nm have a very low coercivity (Hc) and relative remnant magnetization (Mr/Ms), which is unfavorable for magnetic fluid hyperthermia. In contrast, cobalt ferrite (CoFe2O4) particles of the same size have a very high Hc and Mr/Ms, which is magnetically too hard to obtain suitable specific heating power (SHP) in hyperthermia. For the optimization of the magnetic properties, the Fe2+ ions of magnetite were substituted by Co2+ step by step, which results in a Co doped iron oxide inverse spinel with an adjustable Fe2+ substitution degree in the full range of pure iron oxide up to pure cobalt ferrite. The obtained magnetic nanoparticles were characterized regarding their structural and magnetic properties as well as their cell toxicity. The pure iron oxide particles showed an average size of 8 nm, which increased up to 12 nm for the cobalt ferrite. For ferrofluids containing the prepared particles, only a limited dependence of Hc and Mr/Ms on the Co content in the particles was found, which confirms a stable dispersion of the particles within the ferrofluid. For dry particles, a strong correlation between the Co content and the resulting Hc and Mr/Ms was detected. For small substitution degrees, only a slight increase in Hc was found for the increasing Co content, whereas for a substitution of more than 10% of the Fe atoms by Co, a strong linear increase in Hc and Mr/Ms was obtained. Mossbauer spectroscopy revealed predominantly Fe3+ in all samples, while also verifying an ordered magnetic structure with a low to moderate surface spin canting. Relative spectral areas of Mossbauer subspectra indicated a mainly random distribution of Co2+ ions rather than the more pronounced octahedral site-preference of bulk CoFe2O4. Cell vitality studies confirmed no increased toxicity of the Co-doped iron oxide nanoparticles compared to the pure iron oxide ones. Magnetic heating performance was confirmed to be a function of coercivity as well. The here presented non-toxic magnetic nanoparticle system enables the tuning of the magnetic properties of the particles without a remarkable change in particles size. The found heating performance is suitable for magnetic hyperthermia application.

Biocompatible Magnetic Fluids of Co-Doped Iron Oxide Nanoparticles with Tunable Magnetic Properties.

We carry out Monte Carlo simulations to study the effective magnetic moment mu(eff) in the low-field region of magnetic multicore nanoparticles. Transmission electron microscopy and scanning electron microscopy images show that these particles contain a number of magnetic nanocrystals (MNCs) randomly packed in a single cluster of total volume V(tot). We illustrate how the initial magnetic susceptibility chi(0) of magnetic multicore nanoparticles can be straightforward derived from mu(eff) computed at zero magnetic field. We observe that dipolar interactions between MNCs and polydispersity of the MNCs contribute to increase and to decrease mu(eff)/V(tot), respectively, while magnetic anisotropy of the MNCs does not show any effect. In all three cases, mu(eff)/V(tot) can be described by a linear relation to (mu B/k(B)T)(2) that we analytically derived for low applied fields.

Effective magnetic moment of magnetic multicore nanoparticles

Reversible addition–fragmentation chain transfer (RAFT) polymerization is an increasingly popular method of controlled radical polymerization and remarkable advances is made in recent years. This polymerization technique offers great chances for more sustainable routes to obtain tailor-made polymers with high precision. This article may be of interest not only for readers familiar with the technique, but also to newcomers to the field or colleagues, who are looking for more sustainable or safer polymerization techniques to obtain an extensive number of possible polymer structures. After an introduction to RAFT polymerization, different novel paths to carry out RAFT polymerization are discussed in terms of their potential and also advancements in the polymerization technology such as polymerization induced self-assembly or carrying out the polymerization in continuous flow reactors are highlighted. At the end some upcoming application areas of polymers prepared by RAFT are presented.

https://hal.archives-ouvertes.fr/hal-03377914/document

Polymerizations by RAFT: Developments of the Technique and Its Application in the Synthesis of Tailored (Co)polymers

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 in...

Multiparametric Magnetic Particle Spectroscopy of CoFe2O4 Nanoparticles in Viscous Media

Cononsolvency in the ‘drunken’ state: the thermoresponsiveness of a new acrylamide copolymer in water–alcohol mixtures

Magnetic hyperthermia is a technique that describes the heating of material through an external magnetic field. Classic hyperthermia is a medical condition where the human body overheats, being usually triggered by a heat stroke, which can lead to severe damage to organs and tissue due to the denaturation of cells. In modern medicine, hyperthermia can be deliberately induced to specified parts of the body to destroy malignant cells. Magnetic hyperthermia describes the way that this overheating is induced and it has the inherent advantage of being a minimal invasive method when compared to traditional surgery methods. This work presents a particle system that offers huge potential for hyperthermia treatments, given its good loss value, i.e., the particles dissipate a lot of heat to their surroundings when treated with an ac magnetic field. The measurements were performed in a low-cost custom hyperthermia setup. Additional toxicity assessments on Jurkat cells show a very low short-term toxicity on the particles and a moderate low toxicity after two days due to the prevalent health concerns towards nanoparticles in organisms.

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

This paper investigates the dynamic ac susceptibility (ACS) and the Brownian relaxation time of magnetic nanoparticles (MNPs) in dc magnetic fields with arbitrary orientations with respect to the ac magnetic field. A CoFe2O4 MNP sample, dominated by Brownian relaxation, is used to perform ACS measurements in an ac magnetic field with a constant amplitude of 0.2 mT (from 2 to 3000 Hz) and a superposed dc magnetic field with amplitudes ranging from 0 to 5 mT. Experimental results indicate that the ACS and Brownian relaxation time are significantly affected not only by the strength but also by the orientation of the dc magnetic field. Moreover, a mathematical model is proposed to analyze the ACS and Brownian relaxation time in dependence of the orientation of the dc magnetic field, which extends the established models parallel or perpendicular to arbitrary-oriented dc magnetic fields. Experimental results indicate that the good fitting between the experimental data (ACS and Brownian relaxation time) and the proposed models demonstrates the feasibility of the proposed model for the description of ACS and Brownian relaxation time in arbitrary-orientated ac and dc magnetic fields.

Magnetic field orientation dependent dynamic susceptibility and Brownian relaxation time of magnetic nanoparticles

The dipole strength of magnetic particles in a suspension is obtained by a graphical rectification of the magnetization curves based on the inverse Langevin function. The method yields the arithmetic and the harmonic mean of the particle distribution. It has an advantage compared to the fitting of magnetization curves to some appropriate mathematical model: It does not rely on assuming a particular distribution function of the particles.

/pdf/measuring-magnetic-moments-of-polydisperse-ferrofluids-4iuue2t9nj.pdf

Niklas Lucht

Papers

Multiparametric Magnetic Particle Spectroscopy of CoFe2O4 Nanoparticles in Viscous Media

Cononsolvency in the ‘drunken’ state: the thermoresponsiveness of a new acrylamide copolymer in water–alcohol mixtures

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

Magnetic field orientation dependent dynamic susceptibility and Brownian relaxation time of magnetic nanoparticles

Measuring magnetic moments of polydisperse ferrofluids utilizing the inverse Langevin function