The surface-enhanced Raman scattering substrate of Ag–Ag nanocap arrays are prepared by depositing Ag film onto two-dimensional (2D) polystyrene colloidal nanosphere templates. When the original colloidal arrays are used as the substrate for Ag deposition, surface-enhanced Raman scattering (SERS) enhancements show the strong size-dependence behaviours. When O2-plasma etched 2D polystyrene templates are used as the substrate for Ag deposition to form nanogaps, the gap sizes between adjacent Ag nanocaps from 5 to 20 nm generate even greater SERS enhancements. When SiO2 coverage is deposited to isolate the Ag nanocaps from the neighbours, the SERS signals are enhanced more. The significant SERS effects are due to the coupling between Ag nanocaps controlled by the distance, which enhances the local electric-field intensity. Copyright © 2013 John Wiley & Sons, Ltd.