Electron spin resonance spectroscopy for immunoassay using iron oxide nanoparticles as probe

摘要

AbstractWith the help of iron oxide nanoparticles, electron spin resonance spectroscopy (ESR) was applied to immunoassay. Iron oxide nanoparticles were used as the ESR probe in order to achieve an amplification of the signal resulting from the large amount of Fe3+ion enclosed in each nanoparticle. Rabbit IgG was used as antigen to test this method. Polyclonal antibody of rabbit IgG was used as antibody to detect the antigen. Iron oxide nanoparticle with a diameter of either 10 or 30?nm was labeled to the antibody, and Fe3+in the nanoparticle was probed for ESR signal. The sepharose beads were used as solid phase to which rabbit IgG was conjugated. The nanoparticle-labeled antibody was first added in the sample containing antigen, and the antigen-conjugated sepharose beads were then added into the sample. The nanoparticle-labeled antibody bound to the antigen on sepharose beads was separated from the sample by centrifugation and measured. We found that the detection ranges of the antigen obtained with nanoparticles of different sizes were different because the amount of antibody on nanoparticles of 10?nm was about one order of magnitude higher than that on nanoparticles of 30?nm. When 10?nm nanoparticle was used as probe, the upper limit of detection was 40.00?μg?mL?1, and the analytical sensitivity was 1.81?μg?mL?1. When 30?nm nanoparticle was used, the upper limit of detection was 3.00?μg?mL?1, and the sensitivity was 0.014 and 0.13?μg?mL?1depending on the ratio of nanoparticle to antibody.Graphical abstractSchematic diagram of procedure and ESR spectra