Water-Stable Superferromagnetic Nanoparticle Chains Break the Langevin Resolution Limit in Magnetic Particle Imaging
Year: 2026
Type: preprint
Abstract: Magnetic particle imaging (MPI) localizes superparamagnetic iron oxide tracers through their nonlinear magnetization response, but its spatial resolution is bounded by the Langevin behavior of independent magnetic moments, confining clinical tracers to point spread functions (PSFs) near 10 mT and limiting clinical tracer resolution to the centimetre scale in humans. Superferromagnetic iron oxide (SFMIO) tracers — linear chains of dipole-coupled cores that reverse cooperatively — surpass this limit, yet have remained confined to organic solvents, because the charged corona required for aqueous colloidal stability generates an electrostatic repulsion opposing the dipolar attraction that drives chain assembly. Here, a water-stable SFMIO tracer is reported. Monodisperse ~26 nm cores are grown by thermal decomposition, magnetophoretically enriched, encapsulated in poly(maleic anhydride-alt-1-octadecene) to a ~2 nm shell, and assembled into chains under a uniform field at 1.5× phosphate-buffered saline, where screening balances dipolar attraction. The tracer exhibits a mean PSF full-width at half-maximum of 4.3 ± 0.3 mT at 20 mT and 20 kHz across three independent syntheses — 2.6-fold narrower than the preclinical reference tracer VivoTrax, and equivalent to 0.67 mm at a 6.4 T m−1 gradient. The measured coercivity, 12.1 mT, matches the 12.0 mT predicted by a positive-feedback dipolar model parameterized by TEM-measured geometry and a literature-bounded saturation magnetization, confirming cooperative avalanche reversal within structurally static chains.
Source: ChemRxiv
Institution: University of California, Berkeley
Subfield: Biomedical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7204891948
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