(118d) Design and Properties of Magnetic Particle Imaging (MPI) Tracers Using Nitrodopa Anchored Coatings.

Magnetic particle imaging (MPI) is an emerging biomedical imaging technology that involves the use of iron oxide nanoparticles as tracers. Colloidal stability in biological environments is crucial to maintain resolution and sensitivity of tracers engineered for MPI applications such as blood pool imaging and cell tracking. Common methods of synthesis of high-quality iron oxide nanoparticles yield hydrophobic particles that are not suitable for such applications. A large body of work has explored phase transfer methods previously in the context of applications such as hyperthermia and magnetic resonance imaging contrast. However, MPI tracer design requirements differ from these applications in terms of size and magnetic properties of the inorganic core. As these properties affect the strength of magnetic attraction, it is important to re-evaluate methods of phase transfer and nature of particle coatings to achieve colloidal stability for tracers engineered for high sensitivity and resolution in MPI. Here, we report on the design and characterization of superparamagnetic iron oxide nanoparticle tracers optimized for MPI and phase-transferred to aqueous media using a 6-nitro-L-3,4 dihydroxyphenylalanine (nitroDOPA) anchor group conjugated to a polyethylene glycol chain (PEG-nitroDOPA). The nitroDOPA anchor group was selected due to its reported high affinity for the surface of iron oxide nanoparticles resulting in practically irreversible binding. At present, we have successfully synthesized the PEG-nitroDOPA polymer. We have also successfully stabilized iron oxide nanoparticles synthesized in our lab in aqueous media using the synthesized PEG-nitroDOPA, thus showing that despite the difference in diameter between the nanoparticles used in MPI (20-25 nm) and those reported in literature (typically 8-10 nm), the colloidal stability of the iron oxide nanoparticles is achieved. Dynamic light scattering (DLS) measurements of the iron oxide nanoparticles stabilized in water show a hydrodynamic diameter of less than 100 nm. Ongoing work seeks to reduce this further to ~50 nm range while preserving stability in biological environments and maintaining MPI sensitivity and resolution and evaluate blood circulation lifetime for the particles using non-invasive MPI assessment.