Large surface-enhanced Raman scattering from nanoporous gold film over nanosphere

Metal film over nanosphere (MFON) prepared by nanosphere lithography (NSL) is a widely used surface-enhanced Raman scattering (SERS) substrate for practical applications because of its large, facile, and reproducible SERS properties. The SERS "hot spot" of MFON mainly originates from the sharp crevices between adjacent metallic half-domes. However, these sharp crevices are rare for MFON, which limits the further improvement of Raman signals. Here, we report a simple strategy, which combines NSL with dealloying, to create a nanoporous gold film over nanosphere (NPGFON) with 3D distributed hot spots. It was demonstrated that NPGFON can generate more than 35 times higher Raman enhancement than conventional gold film over nanosphere (AuFON) structure. The large SERS enhancement of NPGFON mainly originates from two aspects. One is the large surface area introduced by the internal nanoporous structures. The other is the abundant hot spots that locate both near the sharp crevices between adjacent half-domes and in the widely distributed nanopores. The SERS performances of NPGFON can be adjusted by its pore size, gap size, and period.