The development of rapid, highly sensitive detection methods for α-fetoprotein (AFP) is very important. As hepatocellular carcinoma is closely related to the level of AFP in the blood, it is necessary to maintain an AFP concentration below the safety limit. In this paper, we propose a universal, rapid, sensitive, and highly specific immunoassay system utilizing gold nanoparticles (AuNPs) and surface-enhanced Raman scattering (SERS). This new system features a sandwich structure combining mercaptobenzoic acid-labeled immunogold nanoparticles with the antigen and the antibody atop a pre-designed substrate made of a glass slide modified with AuNPs. This SERS-based immunoassay can detect AFP concentrations as low as 100 pg/ml, which is a significant improvement on the capabilities of the enzyme-linked immunosorbent assay method. A good linear relationship between the SERS peak intensity and the logarithm of antigen concentrations (from 1 ng/ml to 100 ng/ml) was observed. This technique provides an effective model for the detection of biomarkers in medical diagnostics, criminal investigation, and other fields. Copyright © 2013 John Wiley & Sons, Ltd.