Toward theranostic nanoparticles: CB[7]-functionalized iron oxide for drug delivery and MRI

Iron oxide (γ-Fe₂O₃) nanoparticles (NPs) were efficiently coated with the water soluble macrocycle cucurbit[7]uril (CB[7]) by microwave heating. Density functional theory (DFT) calculations support a binding model in which the carbonyl oxygens of CB[7] coordinate directly to surface Fe³⁺ ions. The modified particles (CB[7]NPs) are stable under a wide pH range (2-12) and have a transverse relaxivity, R₂, of 113 s^-1 mM^-1. Nile red (NR) dye was loaded into the cavities of the surface-adsorbed CB[7]s, and intracellular delivery of the dye to HCT116 cells was observed by confocal laser scanning microscopy. The dye-loaded particles (CB[7]NPs⊃NR) have a R₂ of 172 s^-1 mM^-1. The stability, biocompatibility, and dual purpose functionality (drug delivery and magnetic resonance imaging) of the CB[7]NPs herald the theranostic potential of this system.