Flash nanoprecipitation of magnetic particle imaging tracers with tunable performance.

Magnetic particle imaging (MPI) is a novel biomedical imaging modality where biocompatible magnetic nanoparticle (MNP) tracers produce a quantitative signal for imaging applications like pharmacokinetics studies, blood pooling, cell tracking, and more. Improvements to tracer performance are generally made through the alteration of the synthesis mechanism and post-synthesis surface modification tailored to different applications. However, relying on synthesis alone to modify MPI performance can be difficult and time consuming. This study utilized flash nanoprecipitation, a method of MNP encapsulation, to vary the MPI performance of tracers. Herein, composite nanoparticle tracers were produced by precipitating hydrophobic iron oxide nanoparticles and homopolymer in water and stabilizing them with an amphiphilic block copolymer. By increasing the concentration of homopolymer used in precipitation, composite nanoparticle tracers with a range of physical properties and MPI performances were obtained, until a peak MPI performance was achieved and after which additional homopolymer did not further improve performance. Two pre-clinical applications of this work were demonstrated; the first was an