Highly cross-linked and biocompatible polyphosphazene-coated superparamagnetic Fe₃O₄ nanoparticles for magnetic resonance imaging

Highly cross-linked and biocompatible poly(cyclotriphosphazene-co-4, 4′-sulfonyldiphenol) (PZS) were used to directly coat hydrophilic superparamagnetic Fe₃O₄ nanoparticles by a facile but effective one-pot polycondensation. The obtained core-shell Fe₃O ₄@PZS nanohybrids were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) and X-ray diffraction spectra. Interesting, the size and T₂ relaxivity of Fe₃O₄@PZS increased with increasing the mass ratio of Fe₃O₄ to PZS. All these nanohybrids could be internalized by HeLa cells but show negligible cytotoxicity. The PZS layer slowly degraded into less dangerous forms such as 4,4′-sulfonyldiphenol, phosphate and ammonia at neutral or acid atmosphere. Considering their excellent water dispersibility, colloidal and chemical stability, magnetic manipulation, and magnetic resonance imaging (MRI) properties, Fe₃O₄@PZS nanohybrids have great potential in MRI diagnosis of cancer.