Surface-Enhanced Raman Scattering (SERS) is emerging as a promising strategy for the quantification of immunoglobulin G (IgG) due to its inherent high sensitivity and specificity; however, it remains challenging to integrate SERS detection with a microfluidic system in a simple, efficient and low-cost manner. Here, we report on a novel bifunctional plasmonic-magnetic particle-based immunoassay, in which plasmonic nanoparticles act as soluble SERS immunosubstrates, whereas magnetic particles are for promoting micromixing in a microfluidic chip. With this novel SERS immunosubstrate in conjunction with the unique microfluidic system, we could substantially reduce the assay time from 4 hours to 80 minutes as well as enhance the detection specificity by about 70% in comparison to a non-microfluidic immunoassay. Compared to previous microfluidic SERS systems, our strategy offers a simple microfluidic chip design with only one well for mixing, washing and detection.