Nanoparticle coated microspheres are composed of two or more materials with a core/shell structure and exhibit unique abilities that allow amplification of trace targets in immunoassays. The preparation of nanoparticle coated microspheres can be accomplished using three main strategies: (1) in-situ, (2) ex-situ, and (3) hollow sphere methods. Antibodies or biomolecules can be immobilized on the surface of nanoparticle coated microspheres or hollow spheres to carry out detection of targets using surface-enhanced resonance spectroscopy (SERS), fluorescence, electrochemistry, and many others. Using these particles as antibody carriers in SERS-based immunoassays, broad dynamic range and low detection limits, and improved selectivity can be realized. By assistance of nanoparticle coated microspheres in immunoassays, improved sensitivity and selectivity has been realized. In this review, nanoparticle coated microsphere generation, recent applications, and future potential with respect to immunoassays are discussed.