Surface modification γ-Fe2O3(03 @ SiO2 magnetic nanoparticles for the controlled interaction with biomolecules

Modifying the surface of magnetic nanoparticles (MNPs) to allow for controlled interaction with biomolecules enables their implementation in biomedical applications such as contrast agents for magnetic resonance imaging, labels in magnetic biosensing or media for magnetically assisted bioseparation. In this paper, self-assembly of trialkoxysilanes is used to chemically functionalize the surface of gamma-Fe2O3 @ SiO2 core-shell particles. First, the silane deposition procedure was optimized using infrared analysis in order to obtain maximum packing density of the silanes on the particles. The surface coverage was determined to be similar to 8 x 10(14) molecules/cm(2). It was shown that the magnetic,'crystalline, and morphological properties of the MNPs were not altered by deposition of a thin silane coating. The optimized procedure was transferred for the deposition of alclehyde and poly(ethylene glycol) (PEG) presenting silanes. The presence of both silanes on the particle W surface was confirmed using XPS and FTIR. The interaction of proteins with silane-modified MNPs was monitored using a Bradford protein assay. Our results demonstrate that, by introducing aldehyde functions, the MNPs are capable of covalently binding human IgG while retaining their specific binding capacity. Maximum surface coverage occurs at 46 mu g antibodies per mg particle, which corresponds to 35 antibodies bound to an average sized MNP (54 rim in diameter). The human IgG functionalized MNPs exhibit a high degree of specificity (similar to 90%) and retained a binding capacity of 32%. Using the same approach, streptavidin was coupled onto the MNPs and the biotin binding capacity was determined using biotinylated fluorescein. At maximum surface coverage, a biotin binding capacity of 1500 pmol/mg was obtained, corresponding to a streptavidin activity of 76%. On the other hand, by introducing PEG functions the non-specific adsorption of serum proteins W could be significantly suppressed down to similar to 3 mu g/mg. We conclude that self-assembly of silane cc films creates a generic platform for the controlled interactions of MNPs with biomolecules.