This project focusses on the synthesis and characterization of superparamagnetic iron nanoparticles (FeNPs) for magnetic particle imaging (MPI) applications. MPI is an emerging non-invasive tomographic technique that directly detects superparamagnetic nanoparticle tracers within the body. Various synthesis methods are being investigated to obtain pure iron nanoparticles that can produce a higher MPI signal when compared to current iron oxide nanoparticle tracers.  

Background

Magnetic particle imaging (MPI) is an imaging modality that can potentially offer improvements over current X-ray imaging and CT scan techniques. These improvements include real-time 3D imaging, increased image contrast and sensitivity, and increased compatibility with patients (i.e. patients with Chronic Kidney Disease who cannot take iodine tracers for CT scans). The tracers used with MPI are superparamagnetic nanoparticles, as superparamagnetic properties are critical to provide the resolution and sensitivity of an MPI image. To optimize the potential of MPI, efforts are focused on developing pure iron nanoparticles with optimal physical and magnetic characteristics. Ideal iron nanoparticles may also have applications in other biomedical applications such as magnetic resonance imaging (MRI) or magnetic hyperthermia.

Characterization

Certain physical characteristics of iron nanoparticles can contribute to the magnetic properties of the FeNPs. The goal is to produce nanoparticles with ideal magnetic sensitivity (response to a magnetic field) and low coercivity (magnetization after magnetic field exposure ceases). It was found that nanoparticle characteristics like particle size, crystallinity, and alpha-iron content had the largest effects on the previously mentioned magnetic properties. The following is a list of characterization methods used to assess the physical and magnetic properties of the nanoparticles:

Mössbauer Spectroscopy

This spectroscopic technique is used to identify the iron composition of the nanoparticles, primarily to distinguish if there is a presence of pure iron or iron oxide. https://www.utsi.edu/research/research-centers/mossbauer-laboratory/

X-Ray Diffraction (XRD)

The crystallinity of the FeNPs have a significant effect on magnetic properties; with higher crystallinity being more favorable. X-ray diffraction allows for the crystallinity of the samples to be measured by measuring the diffracted x-rays from a sample after incident x-rays are directed at the sample.

Transmission Electron Microscopy (TEM)

This technique is used to assess the size, shape and dispersibility of the nanoparticles. Nanoparticle sizes are analyzed using ImageJ software.  

Superconducting Quantum Interference Device (SQUID) Magnetometry

SQUID magnetometry is used to measure the magnetic sensitivity and coercivity of the FeNPs. This is done by detecting the minute magnetic fields from the nanoparticles with a superconducting detector coil that outputs a voltage which can be translated to Teslas (magnetic flux density).

Recent Activities and Progress

Various synthesis methods have been investigated to fabricate pure iron nanoparticles for MPI applications.

Solvent-Surfactant Syntheses

A series of solvent-surfactant reactions were conducted with varying surfactants to investigate the effects different surfactants have on nanoparticle size. These reactions were conducted by reacting an iron precursor with a mixture of solvents and a surfactant under a Schlenk line to limit oxygen exposure. A surfactant was found to provide the ideal size distribution of the nanoparticles.

Solid-Solid Reduction Reactions

Iron-oxide nanoparticles were synthesized, and silica coated. The silica coated iron oxide nanoparticles reacted with a reducing agent in a vacuum-sealed vessel at various temperatures to form pure, crystalline iron nanoparticles. This reaction method is still being tested and further work in testing various silica coating thicknesses is being explored. 

Future Plans

New synthesis methods will be investigated until iron nanoparticles with ideal physical and magnetic properties are obtained. Once ideal nanoparticles are yielded, the next area of experimentation will be the utilization of organic coatings to increase the biocompatibility of nanoparticles in the human body.

UTSI Researchers

Collaborators

Dr. Todd Giorgio

Professor of Biomedical Engineering

Vanderbilt University

Sydney Henriques

Biomedical Engineering PhD Candidate

Vanderbilt University

Dr. Carlos M. Rinaldi-Ramos

Professor of Biomedical Engineering

University of Florida