Heterogeneous nanoparticles are considered to be one of ideal materials for future biomedical applications because they can give, in a single nanoparticle, multifunctional capabilities such as targeting, imaging, and therapy. Many efforts have been devoted to the synthesis of these nanoparticles. The growth mechanism which plays a vital role in the rational design and precise fabrication of such particles has not been explored yet. Here we propose mechanisms for overgrowth of single gold/polystyrene dimeric nanoparticles by exploiting single particle scattering spectra. Three patterns of scattering spectra are readily differentiated and overgrowth mechanisms that correspond to each scattering spectrum are also proposed.