Surface-enhanced Raman scattering (SERS) on metallic nanostructures has been widely used as a highly sensitive bio/chemo-sensing tool due to the tremendous electromagnetic (EM) enhancement.Despite the prosperous developments in SERS toward practical applications, there are still a number of problems awaiting to be solved, an important one being the complexity of the spectral information including the appearance of the fluorescent background and the abnormal Raman features.