Magnetic nanoclusters with hydrophilic spacing for dual drug delivery and sensitive magnetic resonance imaging

Magnetic Block Ionomer Clusters (<i>MBIClusters</i>) with hydrophilic ionic cores and nonionic coronas have been prepared that have ultrahigh transverse NMR relaxivities together with capacities for incorporating high concentrations of polar antibiotic payloads. Magnetite-polymer nanoparticles were assembled by adsorbing the polyacrylate block of an aminofunctional poly(ethylene oxide-<i>b</i>-acrylate) (H₂N-PEO-<i>b</i>-PAA) copolymer onto magnetite nanoparticles. The PEO blocks extended into aqueous media to keep the nanoparticles dispersed. Amines at the tips of the H₂N-PEO corona were then linked through reaction with a PEO diacrylate oligomer to yield <i>MBIClusters</i> where the metal oxide in the precursor nanoparticles were distinctly separated by the hydrophilic polymer. The intensity average spacing between the magnetite nanoparticles within the clusters was estimated to be ~50 nm. These <i>MBIClusters</i> with hydrophilic intra-cluster space had transverse relaxivities (<i>r₂'s</i>) that increased from 190 to 604 s^-1 mM Fe^-1 measured at 1.4 T and 37 °C as their average sizes increased. The clusters were loaded with up to ~38 wt% of the multi-cationic drug gentamicin. MRI scans focused on the livers of mice demonstrated that these <i>MBIClusters</i> are sensitive contrast agents.