Single Molecule Surface-Enhanced Raman Spectroscopy\nwithout Nanogaps

Abstract

We provide conclusive proof of single\nmolecule (SM) detection by\nsurface-enhanced Raman spectroscopy (SERS) for discrete Ag triangular\nnanopyramids prepared via nanosphere lithography (NSL). While the\nobservation of SMSERS has been well-demonstrated using various chemically\nsynthesized nanoparticle substrates, they have a high degree of polydispersity\nin shape, size, and aggregation state resulting in an interest to\ndevelop more reproducible and uniform nanoparticles. Here triangular-based\nnanopyramids were characterized by scanning electron microscopy to\nconfirm their geometry and interparticle spacing. Then the isotopologue\napproach with Rhodamine 6G was used to conclusively prove SM sensitivity\nfor the individual nanoparticles. NSL’s straightforward, simple\nfabrication procedure produces large active arrays. Furthermore, the\ntunable localized surface plasmon resonance makes NSL prepared substrates\neffective for the detection of resonant molecules by SMSERS.