The adsorption of p-aminothiophenol (PATP) molecule on the gold electrode was investigated. The result suggests that PATP was adsorbed perpendicularly onto the substrate. By immobilizing goat anti-mouse IgG on a glass slide modified by special organic molecules, the antibody/antigen/reporter-labeled immunogold nanoparticle sandwich assay was build for surface-enhanced Raman spectroscopy (SERS) measurements. The p-aminothiophenol (PATP) was used as SERS-reporter molecule. Thus the authors can identify the single type biospecific species by SERS signal of the reporter molecules which are coimmobilized with antibody molecules in gold colloids.