The interaction, stability and response to an external stimulus of iron oxide nanoparticle–casein nanocomplexes

The interaction of iron oxide nanoparticles with casein micelles was studied using Dynamic Light Scattering (DLS) size measurement, Ultraviolet–visible (UV–vis) spectroscopy, Fourier Transform InfraRed (FTIR) spectroscopy, ThermoGravimetric Analysis (TGA), rheology and phase contrast microscopy. The whole milk and skimmed milk treated nanocomplex show an absorption peak at 196 nm, due to the peptide bond of casein. The DLS studies show that the milk treated nanocomplex of average primary particle size ∼38 nm form hydroclusters of size ∼615 nm that disintegrate into smaller clusters upon sonication. The FTIR spectrum of skimmed milk treated nanocomplex shows the characteristic peaks of casein and the nanoparticles. The peaks at 3365 cm−1, 1722 cm−1, 1652 cm−1 and 1585 cm−1 (of casein) and a broad peak at 585 cm−1 (of FeO bond vibration of Fe3O4) were observed for the nanocomplex. The TGA results of skimmed milk treated nanocomplex show a weight loss of ∼13.3%. The rheological studies show that skimmed milk treated nanocomplex exhibit good mechanical stability, whereas the uncoated nanoparticles exhibit poor mechanical stability. The response of uncoated nanoparticles and milk treated nanocomplex to an applied magnetic field shows that iron oxide–casein nanocomplexes reversibly self assemble to form one dimensional chains along the direction of applied magnetic field when the dipolar interaction energy exceeds the thermal energy. Since casein is non-toxic and inexpensive, iron oxide nanoparticle–casein nanocomplexes may find applications in controlled release drug delivery systems.