Surface modification of superparamagnetic iron nanoparticles with calcium salt of poly(γ-glutamic acid) as coating material

Surface-modified magnetite nanoparticles (MNPs) were synthesized by co-precipitation of aqueous solution of ferrous and ferric salts (molar ratio 1:2) upon adding a base followed by calcium salt of poly(γ-glutamic acid) (Ca-γ-PGA) for uniform coating on the surface of MNPs. Both uncoated and Ca-γ-PGA-coated MNPs were characterized using various techniques including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and vibrating sample magnetometric (VSM) studies. Compared with bare MNPs, the IR spectra of coated MNPs showed characteristic peaks of γ-PGA, implying the γ-PGA coating on MNPs did occur. The TEM images depicted an average size of 8-10 nm for bare MNPs and 14 nm for coated MNPs, with their shape being spherical in nature. In the presence of applied magnetic field, a superparamagnetic behavior was observed at room temperature for both bare and Ca-γ-PGA-coated MNPs, with no magnetism left upon magnetic-field removal.