High-performance ferrite nanoparticles through nonaqueous redox phase tuning


From magnetic resonance imaging to cancer hyperthermia and wireless control of cell signaling, ferrite nanoparticles produced by thermal decomposition methods are ubiquitous across biomedical applications. While well-established synthetic protocols allow for precise control over the size and shape of the magnetic nanoparticles, structural defects within seemingly single-crystalline materials contribute to variability in the reported magnetic properties. We found that stabilization of metastable wüstite in commonly used hydrocarbon solvents contributed to significant cation disorder, leading to nanoparticles with poor hyperthermic efficiencies and transverse relaxivities. By introducing aromatic ethers that undergo radical decomposition upon thermolysis, the electrochemical potential of the solvent environment was tuned to favor the ferrimagnetic phase. Structural and magnetic characterization identified hallmark features of nearly defect-free ferrite nanoparticles that could not be demonstrated through postsynthesis oxidation with nearly 500% increase in the specific loss powers and transverse relaxivity times compared to similarly sized nanoparticles containing defects. The improved crystallinity of the nanoparticles enabled rapid wireless control of intracellular calcium. Our work demonstrates that redox tuning during solvent thermolysis can generate potent theranostic agents through selective phase control in ferrites and can be extended to other transition metal oxides relevant to memory and electrochemical storage devices.

Nano letters
Ritchie Chen
Postodoc at Stanford (w/ Karl Deisseroth)
Michael G Christiansen
Postdoc at ETH Zurich (w/ Simone Schuerle)
Polina Anikeeva
Polina Anikeeva
Associate Professor in Materials Science and Engineering
Associate Professor in Brain and Cognitive Sciences
Associate Director, Research Laboratory of Electronics

My goal is to combine the current knowledge of biology and nanoelectronics to develop materials and devices for minimally invasive treatments for neurological and neuromuscular diseases.