Dynamical Magnetic Response of Iron Oxide Nanoparticles Inside Live Cells

TLDR

Magnetic nanoparticles can generate heat under alternating magnetic fields for hyperthermia, but their heating efficiency dramatically decreases when internalized by cells, likely due to clustering or immobilization, yet a quantitative description of these effects is lacking. This study investigates how cell internalization alters the dynamical magnetic response of iron oxide nanoparticles. We employed two experimental approaches to measure magnetic heat losses of nanoparticles inside live cells while preserving viability, assessing their suitability for in‑vitro hyperthermia. AC magnetometry and susceptibility measurements of 11‑ and 21‑nm iron oxide cores revealed that uptake reduces dynamical response, especially for larger particles, and theoretical analysis shows that intracellular clustering—not immobilization—drives this effect, guiding the design of nanostructures with stable heating performance in biological environments.

Abstract

Magnetic nanoparticles exposed to alternating magnetic fields have shown a great potential acting as magnetic hyperthermia mediators for cancer treatment. However, a dramatic and unexplained reduction of the nanoparticle magnetic heating efficiency has been evidenced when nanoparticles are located inside cells or tissues. Recent studies suggest the enhancement of nanoparticle clustering and/or immobilization after interaction with cells as possible causes, although a quantitative description of the influence of biological matrices on the magnetic response of magnetic nanoparticles under AC magnetic fields is still lacking. Here, we studied the effect of cell internalization on the dynamical magnetic response of iron oxide nanoparticles (IONPs). AC magnetometry and magnetic susceptibility measurements of two magnetic core sizes (11 and 21 nm) underscored differences in the dynamical magnetic response following cell uptake with effects more pronounced for larger sizes. Two methodologies have been employed for experimentally determining the magnetic heat losses of magnetic nanoparticles inside live cells without risking their viability as well as the suitability of magnetic nanostructures for in vitro hyperthermia studies. Our experimental results—supported by theoretical calculations—reveal that the enhancement of intracellular IONP clustering mainly drives the cell internalization effects rather than intracellular IONP immobilization. Understanding the effects related to the nanoparticle transit into live cells on their magnetic response will allow the design of nanostructures containing magnetic nanoparticles whose dynamical magnetic response will remain invariable in any biological environments, allowing sustained and predictable in vivo heating efficiency.