We developed a new quantitative detection method for an immunoreaction combining magnetite (Fe3O4) nanoparticle labeling with confocal Raman spectrometry. Magnetite nanoparticles are transparent, Raman active, and easily can be controlled easily by magnets in bimolecular reactions. Human Chorionic Gonadtropin (hCG) was selected as a target molecule for this investigation. Sandwich immunoreaction was performed on a dot-patterned substrate using two anti-hCG antibodies, which were the antibody immobilized on the substrate and the biotinylated antibody. The immunoreaction was microscopically visualized by reacting streptavidin-modified magnetite nanoparticles with the biotinylated antibody on the substrate. The adsorbed magnetite nanoparticles on the dot pattern were detected by Raman intensity imaging. A good linear relation between the integrated Raman intensity spectra at 220 cm-1 and hCG concentration was gained. This method may be applied toward the detection of other target molecules in the fields of biotechnology and biomedicine.
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