EU-02 Importance of Magnetic Anisotropy in Determining Heating and Imaging Performance of Magnetic Nanoflower Colloids
Creators: Julie Borchers
Kathryn Krycka
Brianna Bosch-Santos 
Eduardo de Lima Correa
Anirudh Sharma
Hayden Carlton
Yanliu Dang
Michael Donahue
Cordula Grüttner
Robert Ivkov
Cindi L. Dennis
Publisher: name: IEEE
Year: 2025

Functionalized magnetic nanoparticles have recently demonstrated efficacy in biomedical applications, such as magnetic nanoparticle hyperthermia (MNPH) and magnetic particle imaging (MPI). The composition, surface stabilization, and nanoparticle structure are all key to determining their performance. Here, we examine two compositions (ferrite and cobalt ferrite) of nanoflowers that consist of a central core with granular “petals.” The magnetic nanoflowers (MNFs) have different surface treatments (ionic surfactant or dextran coating) designed to stabilize them in water via electrostatic or steric repulsion, respectively. To determine the correlation between their structure and function, we characterized the MNFs using techniques including specific loss power (SLP), point spread function, AC susceptibility, small angle neutron scattering (SANS), and torque measurements. For both nanoflower compositions, choice of coating has little effect on MNPH and MPI, but the heating output and the imaging tracer quality of the cobalt ferrite MNFs are greatly reduced relative to the ferrite MNFs. We first determined from SANS that uncoated MNFs form multi-pole-like clusters and loose chains. In contrast, the coated nanoflowers form dipoles with branched chains that tilt in increasing magnetic field. Polarized SANS further reveals that while the magnetization in the ferrite MNFs is uniform, the cobalt ferrite MNFs have a core/shell magnetic structure with a magnetization that is reduced significantly relative to bulk. The shell formation leads to frustration that reduces the effective magnetic anisotropy and the maximum heat generated in MNPH. The reduction in magnetic anisotropy then leads to a more linear response of the magnetic moment of the MNFs to magnetic field, which results in minimal MPI signal. Overall, the magnetic anisotropy, as influenced by the MNF composition, is of primary importance, relative to surface stabilization and colloidal structure, for optimizing performance of these nanoparticles in biomedical applications.
Functionalized magnetic nanoparticles have recently demonstrated efficacy in biomedical applications, such as magnetic nanoparticle hyperthermia (MNPH) and magnetic particle imaging (MPI). The composition, surface stabilization, and nanoparticle structure are all key to determining their performance. Here, we examine two compositions (ferrite and cobalt ferrite) of nanoflowers that consist of a central core with granular “petals.” The magnetic nanoflowers (MNFs) have different surface treatments (ionic surfactant or dextran coating) designed to stabilize them in water via electrostatic or steric repulsion, respectively. To determine the correlation between their structure and function, we characterized the MNFs using techniques including specific loss power (SLP), point spread function, AC susceptibility, small angle neutron scattering (SANS), and torque measurements. For both nanoflower compositions, choice of coating has little effect on MNPH and MPI, but the heating output and the imaging tracer quality of the cobalt ferrite MNFs are greatly reduced relative to the ferrite MNFs. We first determined from SANS that uncoated MNFs form multi-pole-like clusters and loose chains. In contrast, the coated nanoflowers form dipoles with branched chains that tilt in increasing magnetic field. Polarized SANS further reveals that while the magnetization in the ferrite MNFs is uniform, the cobalt ferrite MNFs have a core/shell magnetic structure with a magnetization that is reduced significantly relative to bulk. The shell formation leads to frustration that reduces the effective magnetic anisotropy and the maximum heat generated in MNPH. The reduction in magnetic anisotropy then leads to a more linear response of the magnetic moment of the MNFs to magnetic field, which results in minimal MPI signal. Overall, the magnetic anisotropy, as influenced by the MNF composition, is of primary importance, relative to surface stabilization and colloidal structure, for optimizing performance of these nanoparticles in biomedical applications.