Development of europium doped core-shell silica cobalt ferrite functionalized nanoparticles for magnetic resonance imaging

The size, shape and chemical composition of europium (Eu³⁺) cobalt ferrite (CFEu) nanoparticles were optimized for use as a “multimodal imaging nanoprobe” for combined fluorescence and magnetic resonance bioimaging. Doping Eu³⁺ ions into a CF structure imparts unique bioimaging and magnetic properties to the nanostructure that can be used for real-time screening of targeted nanoformulations for tissue biodistribution assessment. The CFEu nanoparticles (size ∼7.2 nm) were prepared by solvothermal techniques and encapsulated into poloxamer 407-coated mesoporous silica (Si-P407) to form superparamagnetic monodisperse Si-CFEu nanoparticles with a size of ∼140 nm. Folic acid (FA) nanoparticle decoration (FA-Si-CFEu, size ∼140 nm) facilitated monocyte-derived macrophage (MDM) targeting. FA-Si-CFEu MDM uptake and retention was higher than seen with Si-CFEu nanoparticles. The transverse relaxivity of both Si-CFEu and FA-Si-CFEu particles were r₂ = 433.42 mM⁻¹ s⁻¹ and r₂ = 419.52 mM⁻¹ s⁻¹ (in saline) and r₂ = 736.57 mM⁻¹ s⁻¹ and r₂ = 814.41 mM⁻¹ s⁻¹ (in MDM), respectively. The results were greater than a log order-of-magnitude than what was observed at replicate iron concentrations for ultrasmall superparamagnetic iron oxide (USPIO) particles (r₂ = 31.15 mM⁻¹ s⁻¹ in saline) and paralleled data sets obtained for T₂ magnetic resonance imaging. We now provide a developmental opportunity to employ these novel particles for theranostic drug distribution and efficacy evaluations. Statement of Significance A novel europium (Eu³⁺) doped cobalt ferrite (Si-CFEu) nanoparticle was produced for use as a bioimaging probe. Its notable multifunctional, fluorescence and imaging properties, allows rapid screening of future drug biodistribution. Decoration of the Si-CFEu particles with folic acid increased its sensitivity and specificity for magnetic resonance imaging over a more conventional ultrasmall superparamagnetic iron oxide particles. The future use of these particles in theranostic tests will serve as a platform for designing improved drug delivery strategies to combat inflammatory and infectious diseases.