Water-Stable Superferromagnetic Nanoparticle Chains Break the Langevin Resolution Limit in Magnetic Particle Imaging
7 affiliations
- 1Department of Electrical Engineering and Computer Sciences
- 2University of California, Berkeley
- 3Until Labs, Inc.
- 4Department of Materials Science and Engineering
- 5Department of Bioengineering
- 6Graduate Group in Biophysics
- 7Berkeley Pre-Clinical Imaging Core Facility
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.
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BibTeX
@misc{cary2026waterstable,
title = {{Water-Stable Superferromagnetic Nanoparticle Chains Break the Langevin Resolution Limit in Magnetic Particle Imaging}},
author = {Benjamin Cary and Justin Garlepp and Arvind Swamynathan and A. Rahman Mohtasebzadeh and Yifeng Shi and Chinmoy Saayujya and Benjamin D. Fellows and Ruhani Sagar and Ut I Chio and Lucile Zhu and Divya Krishnaswamy and Prithvish Ganguly and Shuqing Zhao and Jared Huzar and Michael F. Wendland and Steven M. Conolly and Grigory Tikhomirov},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15008162/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008162/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Water-Stable Superferromagnetic Nanoparticle Chains Break the Langevin Resolution Limit in Magnetic Particle Imaging
AU - Benjamin Cary
AU - Justin Garlepp
AU - Arvind Swamynathan
AU - A. Rahman Mohtasebzadeh
AU - Yifeng Shi
AU - Chinmoy Saayujya
AU - Benjamin D. Fellows
AU - Ruhani Sagar
AU - Ut I Chio
AU - Lucile Zhu
AU - Divya Krishnaswamy
AU - Prithvish Ganguly
AU - Shuqing Zhao
AU - Jared Huzar
AU - Michael F. Wendland
AU - Steven M. Conolly
AU - Grigory Tikhomirov
PY - 2026
DA - 2026/09/01
PB - ChemRxiv
DO - 10.26434/chemrxiv.15008162/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008162/v1
AB - 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.
ER -