Giant Raman enhancement on nanoporous gold film by conjugating with nanoparticles for single-molecule detection

Hot spots have the contradictively geometrical requirements for both the narrowest interstices to provide strong near-field coupling, and sufficient space to allow entrance of the analytes. Herein, a two-step method is employed to create hot spots within hybrid nanostructures, which consist of self-supported nanoporous gold films with the absorbed probes and subsequent nanoparticle conjugates without surface agents or mechanical motion. The molecules confined into 1 nm interstice exhibit 2.9 × 107 times enhancement in Raman scattering compared to pure nanoporous gold. Giant enhancement primarily results from strong near-field coupling between nanopore and nanoparticle, which is theoretically confirmed by finite-difference time-domain simulation. Excellent detection limits toward 10−11 mol l−1 offer an opportunity to track spatial orientation of single molecule and engineer hybrid nanostructures as commercial SERS substrates.