Fluorescent-magnetic poly(poly(ethyleneglycol)monomethacrylate)-grafted Fe ₃O ₄ nanoparticles from post-atom-transfer-radical- polymerization modification: Synthesis, characterization, cellular uptake and imaging

Water-soluble poly(poly(ethyleneglycol)monomethacrylate)-grafted (P(PEGMA)-grafted) Fe ₃O ₄ nanoparticles synthesized via a solvent-free atom transfer radical polymerization (ATRP) method were conveniently surface-modified with 3-aminopropyltrimethoxysilane as anchor molecules to donate NH ₂ groups. Fluorescent magnetic nanoparticles (MNPs) were then obtained by covalently bonding fluorescein isothiocyanate (FITC) to the NH ₂ groups. The successful modification of the MNP surface was ascertained from FT-IR and XPS analyses, indicating that such a facile post-ATRP modification approach for introducing NH ₂ groups will extend the potential applications of polymer-coated MNPs produced via the ATRP method. The as-synthesized FITC-grafted MNPs (FITC-MNPs) showed good water solubility and stability, and have a uniform hydrodynamic particle size of 36.2 ± 2.2 nm. These nanoparticles are superparamagnetic with a saturation magnetization (M _s) of 23 emu g ^-1, which is sufficient for bioapplications. The uptake of the fluorescent MNPs by macrophage cells is about 2 pg Fe/cell, which is nearly similar to the pristine P(PEGMA)-grafted MNPs with good biocompatibility. Furthermore, an MMT assay using the 3T3 fibroblasts indicates the low cytotoxic effect of the FITC-MNPs. The FITC-MNPs can be efficiently uptaken by breast cancer cells up to 85 pg Fe/cell, which might be due to the high solubility of the P(PEGMA) chains in the cell membranes. Confocal microscope results showed that the FITC-MNPs were located inside the breast cancer cells but not within the cell membranes. These results indicate that FITC-MNPs with both fluorescence and magnetic functionalities have great potential for applications in bioimaging.