Determination of IgG by electron spin resonance spectroscopy using Fe3O4 nanoparticles as probe

A novel electron spin resonance (ESR) spectroscopy method for determination of rabbit IgG was presented. Anti-rabbit IgG antibody was bound to Fe3O4 nanoparticles (FeNPs). The FeNPs were used as probe to give ESR signal. After the optimization of the assay, a molar ratio 500:1 of antibody to FeNPs was selected. The sepharose beads were used as solid phase and used to separate the analyte from the sample solution. Two typical immunoassay formats, sandwich and competitive formats, were applied to the determination of IgG. The analytical sensitivities obtained by sandwich and competitive formats were 0.13 μg mL−1 and 0.56 μg mL−1, respectively. The two formats were applied to the determination of the rabbit IgG in rabbit serum. The diluted sample was directly analyzed and other additional sample treatment was not required. The analytical results of the spiked samples indicated that the recoveries of the analytes were acceptable. Furthermore, the sample preparation time used in this method is shorter than most existing immunoassay methods.