High performance nanoparticles for MPI

The sensitivity of magnetic particle imaging (MPI) depends strongly on the saturation magnetisation of the nanoparticle tracers used, so it should be advantageous to use pure Fe, which has a much higher magnetisation than Fe oxide. For the same reason, pure Fe particles should also perform better than Fe oxide in magnetic nanoparticle hyperthermia (MNH). In medical applications however, pure Fe needs to be encapsulated in a biocompatible shell, so high-performance MPI tracers need to be produced as core-shell particles. We present a gas-phase ultra-high vacuum method to synthesise core-shell nanoparticles containing a pure Fe core and show how to produce liquid suspensions from the gas-phase particles. The core-shell systems produced include Fe@FeO, Fe@Ag and Fe@Al. In the case of Fe@FeO (see Figure 1) the hydrosols showed a record heating performance in response to an RF magnetic field (see Figure 2). The gas-phase method allows independent variation of the core size and shell thickness and also enables some control over the particle shape. The flexibility of the method allows optimization of the nanoparticle performance in both MPI and MNH.