Mixed valence Mn,La,Sr-oxide based magnetic nanoparticles coated with silica nanoparticles for use in an electrochemical immunosensor for IgG

We describe the preparation and properties of mixed valence manganite nanoparticles (NPs) of the type La_0.67Sr_0.33MnO₃ for use in electrochemical immunoassays. The NPs were synthesized using the reverse micelle method and their surface was then functionalized with silica nanoparticles. The resulting NPs (La_0.67Sr_0.33MnO₃@SiO₂) were characterized by X-ray diffraction, scanning electron microscopy and physical property measurements. Their typical diameter is ~200 nm, and the magnetic saturation occurs at 75 emu⋅g‾¹, and both coercive force and hysteresis loop remain at almost zero. The silica NPs immobilized on the La_0.67Sr_0.33MnO₃ NPs have a diameter of ~20 nm. The La_0.67Sr_0.33MnO₃@SiO₂ NPs were used to develop an electrochemical immunoassay for human IgG. Antibody (anti-human IgG) was immobilized on the silica NPs on the magnetic core, and this process was monitored by cyclic voltammetry and square-wave voltammetry. The formation of the immunocomplex (Ab/Ag) on the surface of the electrode was monitored using hexacyanoferrate redox system as the redox marker. The assay has a linear working range up to an IgG concentration of 5 ng⋅mL‾¹, and the detection limit is 0.6 ng⋅mL‾¹. [Figure not available: see fulltext.]