Aqueous immune magnetite nanoparticles for immunoassay

Immune magnetite nanoparticles (MNPs) are prepared by four successive reactions, which are MNPs preparation, silica-coating, surface modification with amino group, and conjugation with bio-molecule, respectively. The crystal structure and morphology of intermediate products are characterized by XRD, TEM and AFM. Qualitative and quantitative assays for amino group on the MNPs’ surface are made by FTIR and Organic Element Assay. Ultraviolet–visible absorption spectrum can indirectly illustrate the quantity of bio-molecule conjugated with MNPs. In addition, specific combination and nonspecific combination of immune MNPs are measured by commercial RIA box. The results show that the size of MNPs prepared is 10 ± 5 nm, and silica-coated MNPs with spinel structure have quasi-spherical morphology. Infrared absorption bands of –NH₂ are appeared around 3380–3200 cm⁻¹ and 1650–1510 cm⁻¹, and the amino group content is 0.5 μmol –NH₂ per mg MNPs. The specific immune combination of immune MNPs is up to 75%, and nonspecific combination is under 5%.